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Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => AC Power and Grounding => Topic started by: John Roll on September 15, 2015, 11:54:57 AM

Title: Generator question
Post by: John Roll on September 15, 2015, 11:54:57 AM
When im in a club, i can run my rig,lighting backline and foh all on 1 20 amp circuit. I did an outdoor show which used a generator to provide power. I was leary but willing to do the best I could. When power up my furman voltage regulator at foh measured 115. So far, so good. As soon as the first note dropped the meter on the regulator dropped as low as it could go. I went into damage control mode and proceeded to tailoring the bass to eliminate the loading. Eventually, I got things stabilized and the show was a success. My questions to the forum are; could the generator have been undersized? I dont remember what it was rated at,but I remember thinking that it would be ok. Could I have used heavier gauge cable from the generator to the stage. I used 14/3. It was a 25' run. Should the genny have had a regulator in line or built in? This was first show using power from a generator. I wAs lucky this time, but I want to be.prepared for the future so I know exactly what to ask for. Thanks.









Title: Re: Generator question
Post by: Mike Pyle on September 15, 2015, 11:57:22 AM
What generator was it?
Title: Re: Generator question
Post by: John Roll on September 15, 2015, 12:02:29 PM
What generator was it?

I wasn't paying attention. It was "industrial" size. It came on it's own trailer. It came from Taylor rental here in Vestal NY
Title: Re: Generator question
Post by: TJ (Tom) Cornish on September 15, 2015, 12:04:03 PM
When im in a club, i can run my rig,lighting backline and foh all on 1 20 amp circuit. I did an outdoor show which used a generator to provide power. I was leary but willing to do the best I could. When power up my furman voltage regulator at foh measured 115. So far, so good. As soon as the first note dropped the meter on the regulator dropped as low as it could go. I went into damage control mode and proceeded to tailoring the bass to eliminate the loading. Eventually, I got things stabilized and the show was a success. My questions to the forum are; could the generator have been undersized? I dont remember what it was rated at,but I remember thinking that it would be ok. Could I have used heavier gauge cable from the generator to the stage. I used 14/3. It was a 25' run. Should the genny have had a regulator in line or built in? This was first show using power from a generator. I wAs lucky this time, but I want to be.prepared for the future so I know exactly what to ask for. Thanks.
Your generator was too small, and probably the wrong type - i.e. construction-grade rather than an inverter generator such as the Honda EU series.  A sudden power draw causes the generator to lug, dropping the voltage and affecting frequency stability. 

To use a generator, you need to know your draw.  A Honda EU3000 would supply a 20A circuit.  I prefer the EU6500 which gives a bit of headroom.  They may be more expensive to rent or buy, but they are worth it.


Title: Re: Generator question
Post by: TJ (Tom) Cornish on September 15, 2015, 12:07:45 PM
I wasn't paying attention. It was "industrial" size. It came on it's own trailer. It came from Taylor rental here in Vestal NY
That's not a lot to go on.  There are trailer mounted air compressors or light towers that may still be a small generator in a large package.  If the only cord in question was 25' long, the issue is still the generator's limited capacity or poor regulation.
Title: Re: Generator question
Post by: John Roll on September 15, 2015, 12:12:45 PM
That's not a lot to go on.  There are trailer mounted air compressors or light towers that may still be a small generator in a large package.  If the only cord in question was 25' long, the issue is still the generator's limited capacity or poor regulation.

I've got a small club rig with 2-JBL PRX 635s over 2/4 QSC HPR 181s along with 4 JBL PRX 612s plus 12 LED PAr64 along with FOH. How do you recommend to calculate the needs of that system?
Title: Re: Generator question
Post by: Kemper Watson on September 15, 2015, 12:56:45 PM
I've got a small club rig with 2-JBL PRX 635s over 2/4 QSC HPR 181s along with 4 JBL PRX 612s plus 12 LED PAr64 along with FOH. How do you recommend to calculate the needs of that system?

Did they provide a spider box? For an outdoor show I'd ask for an Multi-Quip 45 or better. Get them to provide the spider box with 8- 20 amp breakers. And get rid of the 14 gauge extension cords .
Title: Re: Generator question
Post by: Debbie Dunkley on September 15, 2015, 01:05:34 PM
The outdoor show we just did always provides 2x Honda EU3000's and 2x 10 AWG cables at my request. They work like a charm. I use one for PA only and the other for everything else. Never a stutter,  or a drop and 125 v steady from 12.00pm through to 10.45pm. I can even manage to move them on my own ( not far mind but it just goes to show how small they are)
I would love to own a couple.
The bigger beastly looking generators might look like they are more capable but not necessarily so.
Title: Re: Generator question
Post by: Art Hays on September 15, 2015, 01:28:39 PM
Your generator was too small, and probably the wrong type - i.e. construction-grade rather than an inverter generator such as the Honda EU series.  A sudden power draw causes the generator to lug, dropping the voltage and affecting frequency stability. 

As mentioned above inverter generators are clever- they generate the sine wave output via semiconductors.  The output is somewhat independent of the RPM of the engine (which is why they can be quieter at low load).  Non-inverter generators have to try keep RPM constant over all loads to maintain 60Hz.

I second the post above and would think an inverter generator would have superior output regulation.

Title: Re: Generator question
Post by: TJ (Tom) Cornish on September 15, 2015, 01:30:01 PM
Did they provide a spider box? For an outdoor show I'd ask for an Multi-Quip 45 or better. Get them to provide the spider box with 8- 20 amp breakers. And get rid of the 14 gauge extension cords .
This is totally out of the league of the OP's system, and likely represents the difference between getting the gig or the entire event being cancelled.

In my part of the country, an EU6500 rents for $135/day, which provides 30A 240V, with 2 20A 120V circuits on the front panel.  It is also under the 10KW limit where a permit and an inspection are required.  The generator you mention would be closer to $800-$1000 with delivery, permitting, inspection, and monkey business.

I run significantly more gear than the OP, and have had no issues on the EU6500. 
Title: Re: Generator question
Post by: TJ (Tom) Cornish on September 15, 2015, 01:32:48 PM
The outdoor show we just did always provides 2x Honda EU3000's and 2x 10 AWG cables at my request. They work like a charm. I use one for PA only and the other for everything else. Never a stutter,  or a drop and 125 v steady from 12.00pm through to 10.45pm. I can even manage to move them on my own ( not far mind but it just goes to show how small they are)
I would love to own a couple.
The bigger beastly looking generators might look like they are more capable but not necessarily so.
Debbie, a single EU6500 is preferable to two EU3000s.  If you do run more than one generator, make sure that you are connecting the grounds of both generators together with a heavy wire so that any current flowing on ground wires happens on your ground jumper rather than the shield wire of your audio cables.
Title: Re: Generator question
Post by: kel mcguire on September 15, 2015, 01:45:24 PM
Debbie, a single EU6500 is preferable to two EU3000s.  If you do run more than one generator, make sure that you are connecting the grounds of both generators together with a heavy wire so that any current flowing on ground wires happens on your ground jumper rather than the shield wire of your audio cables.

Honda makes a link sync kit for running two of the same model generator. I bought the kit since I rent the EUs quite often.
Title: Re: Generator question
Post by: Debbie Dunkley on September 15, 2015, 02:07:04 PM
Debbie, a single EU6500 is preferable to two EU3000s.  If you do run more than one generator, make sure that you are connecting the grounds of both generators together with a heavy wire so that any current flowing on ground wires happens on your ground jumper rather than the shield wire of your audio cables.


Whoa - wait - what?......... The Gennys and cables are already set up when we get there so what should I be looking for to be sure this is being done right??....This Grounding thing is out of my league
Title: Re: Generator question
Post by: g'bye, Dick Rees on September 15, 2015, 02:15:19 PM
Per Kels post:

http://powerequipment.honda.com/generators/generator-parallel-capability

But I agree with TJ.  Go with a single 6500.  The parallel kits will run the master unit low on fuel before the second unit as they will be loaded in series rather than parallel.  This shortens your run time.
Title: Re: Generator question
Post by: Stephen Kirby on September 15, 2015, 02:16:02 PM
I thought Debbie said she is using them independently.  One for sound.  And the other for lights and any concession stands etc.  I don't think there are any common connections between them.  At least I hope there isn't a DMX controller in the outboard rack screwed to the same rail, or some such.

Would it be better for her to run a distro off the 30A plug?

I fortunately have not had to deal with Genny gigs but I'm trying to understand the options should one ever come up.  I do have a CA plug distro that I could adapt to the 30A on the EU6000 if thats a better way to go.
Title: Re: Generator question
Post by: Kevin Bayersdorfer on September 15, 2015, 05:44:13 PM
I thought Debbie said she is using them independently.  One for sound.  And the other for lights and any concession stands etc.  I don't think there are any common connections between them.  At least I hope there isn't a DMX controller in the outboard rack screwed to the same rail, or some such.

Would it be better for her to run a distro off the 30A plug?

I fortunately have not had to deal with Genny gigs but I'm trying to understand the options should one ever come up.  I do have a CA plug distro that I could adapt to the 30A on the EU6000 if thats a better way to go.
I read, one for PA, second for all other stuff. So if she has say a bass amp powered by the second generator and it is DIed to the board there is your link on the small ground.
Title: Re: Generator question
Post by: Art Hays on September 15, 2015, 05:47:12 PM
But I agree with TJ.  Go with a single 6500.  The parallel kits will run the master unit low on fuel before the second unit as they will be loaded in series rather than parallel.  This shortens your run time.

I tried to learn how paralleling works but couldn't find anything technical.  There parallel cables/kits just connect the two inverter outputs together.  The inverters don't communicate with each other via any other signal lines.  So they must accomplish synchronization by looking only at their outputs or some sort of communication protocol.  Perhaps by sending some type of high frequency signals to each other on top of the 60Hz sine wave?  And by designating master/slave units?

Seems a big disadvantage if they don't each supply 50% to the load when paralleled.

P.S. in my previous post to this thread I incorrectly said one could connect two 110v inverter generators and have the option to get 220v (each running 180 deg out of phase from the other). They don't do this- paralleling always connects the two outputs together so they have to be in phase.
Title: Re: Generator question
Post by: Stephen Kirby on September 15, 2015, 06:04:52 PM
I read, one for PA, second for all other stuff. So if she has say a bass amp powered by the second generator and it is DIed to the board there is your link on the small ground.
In that case, I agree.  Single larger generator.  Anything connected to both systems without them being bonded together is probably asking for trouble.  Especially if one of them starts to go south.

I can understand the comfort of redundancy but never the twain shall meet.

It looks as though the larger model is capable of balancing loads between the two sets of Edison outlets if you turn off the 240 outlet.  Is this better than running a distro out of the 240 outlet and trying to balance the loads manually?
Title: Re: Generator question
Post by: jim whitmer on September 16, 2015, 10:05:32 AM
In my part of the country, an EU6500 rents for $135/day, which provides 30A 240V, with 2 20A 120V circuits on the front panel.  It is also under the 10KW limit where a permit and an inspection are required. 
I run significantly more gear than the OP, and have had no issues on the EU6500.
The 6500 runs 3 or 4 IT4k's for FOH, 5 powered wedges, backline, and smaller led lightshow without issue.
Title: Re: Generator question
Post by: David Allred on September 16, 2015, 01:30:10 PM
General answer - It depends on if you like Burger King or Wendy's. 8)
Title: Re: Generator question
Post by: Debbie Dunkley on September 16, 2015, 02:47:13 PM
Our next show at the same place is next month so I ought to get to the bottom of this before then. I am sure I could get the owner to provide the EU6500 or equivalent but the weight will be a problem possibly. The nice thing about the 3000 is that it is so light compared. If I parallel them, and watch for the first unit running out of gas( which I check periodically during the day anyway), will this cure the grounding issue?w

Edit: as an alternative approach, what about making sure that anything like bass DI (as was mentioned earlier) is connected to the same generator with everything else like lights and miked instruments connected to the other one?
Title: Re: Generator question
Post by: frank kayser on September 16, 2015, 03:40:19 PM
<snip>
If I parallel them, and watch for the first unit running out of gas( which I check periodically during the day anyway), will this cure the grounding issue?

Edit: as an alternative approach, what about making sure that anything like bass DI (as was mentioned earlier) is connected to the same generator with everything else like lights and miked instruments connected to the other one?

If you use the Honda generator parallel kit, no worries about grounding. (other than the regular ground-neutral bonding issues with Honda EU series gennies, and the fact that without the G-N bond, a GFCI is useless)  I do not know if the parallel kit for the EU3000 performs the G-N bond...

Trying to ensure completely isolated loads between generators would be a big headache. You'd have to analyze each and every connection in that light, and hope nothing changes, or you start over.  Also, a single pin1 to ground bond in an XLR cable could sabotage your entire isolated load plan.

frank
Title: Re: Generator question
Post by: Kemper Watson on September 16, 2015, 03:50:13 PM
This is totally out of the league of the OP's system, and likely represents the difference between getting the gig or the entire event being cancelled.

In my part of the country, an EU6500 rents for $135/day, which provides 30A 240V, with 2 20A 120V circuits on the front panel.  It is also under the 10KW limit where a permit and an inspection are required.  The generator you mention would be closer to $800-$1000 with delivery, permitting, inspection, and monkey business.

I run significantly more gear than the OP, and have had no issues on the EU6500.

The MQ 45 is around $400 here. The promoters here always cover the cost
Title: Re: Generator question
Post by: TJ (Tom) Cornish on September 16, 2015, 04:31:32 PM
Our next show at the same place is next month so I ought to get to the bottom of this before then. I am sure I could get the owner to provide the EU6500 or equivalent but the weight will be a problem possibly. The nice thing about the 3000 is that it is so light compared. If I parallel them, and watch for the first unit running out of gas( which I check periodically during the day anyway), will this cure the grounding issue?w

Edit: as an alternative approach, what about making sure that anything like bass DI (as was mentioned earlier) is connected to the same generator with everything else like lights and miked instruments connected to the other one?
Debbie, grounding the generators together is as simple as getting a length of green #10 THHN wire from Home Depot as long as the physical distance between your two generators will be, and then attaching this wire between the grounding screws on the generators.  This is very low-cost, and shouldn't raise any eyebrows from inspectors, as it's clear what you're doing.  This is also much easier than trying to keep track of which loads go where.
Title: Re: Generator question
Post by: TJ (Tom) Cornish on September 16, 2015, 04:36:42 PM
If you use the Honda generator parallel kit, no worries about grounding. (other than the regular ground-neutral bonding issues with Honda EU series gennies, and the fact that without the G-N bond, a GFCI is useless)  I do not know if the parallel kit for the EU3000 performs the G-N bond...

Trying to ensure completely isolated loads between generators would be a big headache. You'd have to analyze each and every connection in that light, and hope nothing changes, or you start over.  Also, a single pin1 to ground bond in an XLR cable could sabotage your entire isolated load plan.

frank
Frank, the G-N bond becomes problematic with two generators paralleled, as technically both generators need to be bonded to trip the respective breakers.  This effectively turns both generator frames into current-carrying conductors, which may or may not be worse than no bond at all.  This is one of the several reasons a single EU6500 is preferable to a pair of smaller generators.

Phil Graham wrote an article series on generators in entertainment power that is a worthwhile read, though fair warning that things do get a bit technical.  http://www.fohonline.com/current-issue/74-tech-feature/8858-generators-and-portable-primer-part-1.html
Title: Re: Generator question
Post by: TJ (Tom) Cornish on September 16, 2015, 04:40:16 PM
The MQ 45 is around $400 here. The promoters here always cover the cost
Which is still 3X the cost of an EU6500/EU7000, and now you're relying on someone else to ensure the generator is delivered and running appropriately - voltage range selection, voltage regulation, phase configuration, etc.  The EU6500 is very difficult to screw up as voltage and frequency regulation is automatic.  The only switch you need to worry about is the 120V or 120V/240V switch, and even then the worst case is it won't work.
Title: Re: Generator question
Post by: Debbie Dunkley on September 16, 2015, 05:02:13 PM
Debbie, grounding the generators together is as simple as getting a length of green #10 THHN wire from Home Depot as long as the physical distance between your two generators will be, and then attaching this wire between the grounding screws on the generators.  This is very low-cost, and shouldn't raise any eyebrows from inspectors, as it's clear what you're doing.  This is also much easier than trying to keep track of which loads go where.

I think that is within my capabilities T.J. …LOL……….. thank you.
Title: Re: Generator question
Post by: Kemper Watson on September 16, 2015, 05:09:08 PM
Which is still 3X the cost of an EU6500/EU7000, and now you're relying on someone else to ensure the generator is delivered and running appropriately - voltage range selection, voltage regulation, phase configuration, etc.  The EU6500 is very difficult to screw up as voltage and frequency regulation is automatic.  The only switch you need to worry about is the 120V or 120V/240V switch, and even then the worst case is it won't work.

I guess I've been spoiled. Same promoters, same generator providers year in and out.. Never an issue..
Title: Re: Generator question
Post by: Stephen Kirby on September 16, 2015, 05:13:21 PM
Debbie, don't know if you remember the days of amps with two wire plugs.  Where you could not only get shocked from the mic but also by brushing into another player who happened to be on the opposite ground reference.

Everything on stage should be at a common ground.  Lights that people can't touch are pushing it.  Having different amps on stage with different grounds is a bad idea.

It seems simpler to have everything on one supply and just let it draw what it does than trying to divide the load between two sources.  I did a couple of outdoor things this summer where there was only two 20A services.  I bonded them together with a poor man's distro but still had to try and work out the loads so that one side didn't get overloaded.  I'm trying to get them to put in a CA outlet so this won't come up.  When these things spill over to the evening and there's no lights they've been lucky nothing bad has happened.  With a decent service we can have lights which will make the event much better.

Edit:  Sodden thought after writing that.  Would running the service from Debbie's two generators to a poor man's distro be okay?  Or does the length of wire create too much current flow?
Title: Re: Generator question
Post by: Art Hays on September 16, 2015, 05:45:05 PM
I'm a little confused by some previous posts.  Please correct my understanding because I'd love to be more educated about this from people who have practical experience.

From the generator schematics I can't see how paralleling two EU2000's is any different from using one EU6500 other than convenience, e.g. capacity issues and how you draw the loads.  Honda generators don't bond Neutral to Ground.  When you parallel two EU2000's you connect each generator's hot (L1) and neutral (N) together through the parallel cable plug connectors (and the grounds are connected together if you connect this third wire under the screw terminals).

The circuit breakers on each generator still work fine because that are in series with the L1 output.  They respond to the amperage flowing in L1.  Likewise I think a GFCI will still work because it only looks at imbalance between L1 and N.

I could see how if the grounds aren't connected this might affect the inverter electronics sync'ing the phases.
Title: Re: Generator question
Post by: Stephen Swaffer on September 16, 2015, 06:45:32 PM
GFCI's will still work regardless of ground presence or absence-if there is a possibility of dangerous current flow.

There are a number of discussions on the AC power forum on this subject.  In general, generators without a bonded neutral are only intended for "cord and plug" connected equipment.  A distro is not "equipment" and thus requires a G-N bond.  This is a critical SAFETY concern.  In a nutshell, if a hot shorts to ground and there is no ground-neutral bond, the breaker will not trip-leaving a dangerous uncontrolled situation.  The ground-neutral bond is vital to allow protective devices to operate as intended.
Title: Re: Generator question
Post by: Stephen Kirby on September 16, 2015, 07:41:06 PM
Hello Steve.  In the absence of a local ground rod as with big generators, is there a reason that small systems like the Hondas don't have ground and neutral bonded in a sort of floating bootleg ground?  Without a hard ground there will still be potential between the generators neutral and anything else that approximates a ground like a scaffold stage set in a concrete parking lot.  Which if a hot shorted to it would energize it without tripping a breaker.  Kind of like the RV hot skin bit.

It seems like you would want a derived ground that you could make common somehow.

Maybe this gets moved to the power/AC forum, but not everyone participating here follows that.
Title: Re: Generator question
Post by: Stephen Swaffer on September 16, 2015, 08:21:50 PM
"Grounding" and "bonding" are 2 separate issues-and this whole topic requires much more in depth than I can go into here.

"Grounding" is primarily lighting protection-"bonding" is more of an equipment/personnel safety issue.  A generator grounded to a ground rod is NOT the same as a generator bonded to a metal stage-even if the stage is grounded to a ground rod.  IMO, bonding is more important than grounding in in these situations-though many focus on grounding.  In any case, it is not the size of penny that determines requirements-it is the use.  When used as a "separately derived" system-powering a distribution system-both grounding and bonding are required by  code.  How far you take it is your responsibility-not mine!

Again, that is really an oversimplification.
Title: Re: Generator question
Post by: Stephen Kirby on September 16, 2015, 08:37:14 PM
I was expecting that in something like Debbie's situation they wouldn't tie the generator's ground and the stage together.  The genny just sits out back running away with stuff plugged into and it's ground potential floating to wherever.  Meanwhile the stage with all the metal exposed to humid east coast air and sitting on moist concrete or in a dirt field is much closer to true ground.  This is an entirely likely scenario for a lounge person doing a little municipal affair.  What happens when someone holding a mic or a guitar grabs hold of part of the stage?  If there is a ground fault in their amp?
Title: Re: Generator question
Post by: Debbie Dunkley on September 16, 2015, 08:38:59 PM
You guys are scaring me !!!
Title: Re: Generator question
Post by: frank kayser on September 16, 2015, 08:48:47 PM
You guys are scaring me !!!
Debbie,
No need to be scared, just be very respectful.

The Honda EU6500 is the gold standard for those needing more than 25 amps or so - without the permit and licensing requited for the bigger Wisperwatt type units.

For up to 25 amps, the EU3000 is the gold standard.  With the proper parallel kit, everything will run fine and be safe. 

There are other things about generator power that one should be aware of.  There are tons of threads on genny power, with not more than a little disagreement on best practices.  There are some basics, and safety trumps all.

frank
Title: Re: Generator question
Post by: David Buckley on September 16, 2015, 10:48:52 PM
I was expecting that in something like Debbie's situation they wouldn't tie the generator's ground and the stage together.  The genny just sits out back running away with stuff plugged into and it's ground potential floating to wherever.  Meanwhile the stage with all the metal exposed to humid east coast air and sitting on moist concrete or in a dirt field is much closer to true ground.

But.... what is "true ground"?  Sure, that stage is sitting on a lot of soil, a physical construct, but "ground" is an electrical construct, and more than that, it is an artificial electrical construct.  "Ground" doesn't exist unless we make it exist.

The problem is that this stuff is both trivially simple, yet gets hard real quick.

The purpose of "ground" in your home or office is so that if a hot conductor comes in contact with "ground" (this is a "fault condition") then there will be a big flash, lots of current will flow, and the circuit breaker will open switching off that hot conductor.  The ground conductor is the same as the neutral.  A short from hot to ground is the same as a short from neutral to ground.  The difference between neutral and ground is that the ground is not ordinarily expected to carry current, only the neutral does that.

The reason that electrical ground exists at all is to make stuff safer.  Lets assume there was no ground, as was common in the USA a few years back.  Lets further assume you have two guitar amplifiers, with wired guitarists connected.  Let us further assume that both amplifiers have a fault each, they have a short in the power cable to the chassis of the guitar amp.  Final assumption is that one short is to one wire of the power cable, and the other amp to the other.  Everything works great until the two guitarists touch each other, and then both guitarists get shocked as the power goes from one mains wire, through the fault in one amp, down the guitar lead, to the guitar, the guitarist, the body contact, the other guitarist, his guitar, the lead, the other amp, and its fault to the other wire.  Ouch.  I've used guitars and amps as an example, but it could be any pair of household or office appliances.

So, the idea of grounding was developed.  The neutral of the power system was connected to "ground", which meant water pipes, the soil outside, the chassis of the guitar amps, everything metal and electrical.   So everything you can touch is grounded, so you cant get a shock between metal stuff.  All this grounded metal stuff provides an "equipotential zone", and you are safe in your equipotential zone.  If a fault condition develops between neutral and ground, nothing bad happens, as they are the same potential.  Approximately.   If a hot conductor touches anything grounded in this equipotential world, then flash, bang, breaker opens.

That's why we do grounding: it provides an equipotential zone where all exposed electrically connected metalwork is connected together ("bonded") to prevent a shock potential developing between stuff.

Phew.

The genny just sits out back running away with stuff plugged into and it's ground potential floating to wherever.    This is an entirely likely scenario for a lounge person doing a little municipal affair.  What happens when someone holding a mic or a guitar grabs hold of part of the stage?  If there is a ground fault in their amp?

What indeed?

If the output of the generator is indeed floating (ie there is no connection between the neutral pin of the outlet and the ground pin) then there is no solid path for current to take from a fault between hot and the ground pin.  Thus with a single hot to ground short, the generator breaker will not open.  Everything connected to this generator will no longer be  "floating" (ie, connected to nothing) but will be connected to the hot (or neutral, depending on the fault) of the generator.

This could be bad, or unnoticeable, depending on a lot of things.  But one thing is sure; if a second fault develops, to the other wire of the plug, then there is the possibility of real danger.

The first and best line of defense here is GFCIs.  Even a small leakage current caused by a fault with a floating generator will be enough to open the GFCI and preserve life.

The second thing is actually the number one rule of sound system engineering; have a single ground for the system.  If there are two (or more) independent generators, common their grounds so you still have a common ground in the system.  Anyone remember the poor mans distro?  That keeps the grounds communed even with different supplies to different parts of the system.

If you are paralleling generators, like the Hondas, I've had no experience of those particular generators, so don't know how they work their magic, and especially in terms of grounding.  The manual says they have a ground terminal, which connects all metal stuff but is not connected to the generator output.  So you would think that step one is join the frame ground terminals together, "just in case".  These are floating ground generators, and many of the RV crowd then link neutral and earth pins, so that the supply looks the same as it would for a house.  If that is possible, that would be a sensible thing to do, as then the supply in a field looks a lot like a supply in a building, with the same sorts of safety advantages as outlined above.  if the generators have integrated GFCIs, that might be harder.

Caveat - there are a number of ways that small generators can be "grounded", before doing anything, be sure to understand how the grounding works.

Title: Re: Generator question
Post by: Stephen Swaffer on September 16, 2015, 11:08:59 PM
The genny just sits out back running away with stuff plugged into and it's ground potential floating to wherever.  Meanwhile the stage with all the metal exposed to humid east coast air and sitting on moist concrete or in a dirt field is much closer to true ground.

Please don't take this personally-I am sure there are plenty of audio and business principles you could school me on-but this statement shows a basic misunderstanding of grounding and bonding issues and how electrical power works.

Debbie,
No need to be scared, just be very respectful.

There are tons of threads on genny power, with not more than a little disagreement on best practices.  There are some basics, and safety trumps all.


Bottom line-if you make a technical mistake and fry some tweeters or let the smoke out of an amp, you can learn from it and be smarter tomorrow.  If you make a mistake with electrical power it is possible that you or someone on stage won't get a chance to do better next time.

I would get an electrician or more importantly someone that understand the issues and have them walk you through an proper setup.  I would recommend using the NEC for the "right way."  Most of the people involved in making those rules are smarter than us-and it has the advantage of being an accepted "industry standard" which in my mind is a good place to be if something bad happens.

Yes, you can often get away with bad practices.  Last week I repaired a service in a home.  There was about 15 feet of floor joist charred by a piece of hot romex.  No one-including the local inspector-understood why-the breaker was sized properly.  In the process, I found that the ground wire was not hooked up correctly-it appears it was about 2" short and so someone did something they judged "good enough".  To compound the problem, the POCO had a bad neutral.  The lack of a ground and proper bond I have seen in many many houses in this area-but in this case this may have contributed to a near miss.  Eventually bad practices and circumstances will cross paths and bad things happen.

Again, take a few minutes, learn how to do it correctly and make it a habit.  For most sound providers, it is probably better put forth a little extra effort and have a known safe method than to try to learn all the exceptions and what you can "get away with."
Title: Re: Generator question
Post by: Robert Lofgren on September 17, 2015, 02:56:02 AM
One thing that I've learnt about generators in general is that e.g. a 10A generator can deliver just that, but not more.

In normal household 10A power you can pull ten times that power for a short burst without tripping a breaker or similar. Think of starting vaccum cleaners that at the starting moment they can draw much more power than rated for.

Since a 10A generator cant deliver any more power than that you run into issues when appliancies draw a large peak power while the average power can be well under the 10A limit.

This means that a generator should be sized for its peak power and not its rms(?) power.
Title: Re: Generator question
Post by: David Allred on September 17, 2015, 07:02:01 AM
General answer - It depends on if you like Burger King or Wendy's. 8)

I must apologize.  I thought the topic was "General question".  I was poking fun at a little pet Peavey I have with non-descript topic names.  "I have a question", "What's wrong?", "Is it broken?", "Sound", etc.
I need to read better.

Title: Re: Generator question
Post by: TJ (Tom) Cornish on September 17, 2015, 07:58:27 AM
I'm glad to see a lively discussion here.  There's been some really good information, and some less-good information posted.  This is a complicated issue and is worth the time to talk about it.

RE - Honda parallel kit - there is a paralleling kit, but that wasn't how Debbie was using her pair of EU3000s - she was plugging some things into one, and other things into the other.  There are pros and cons to both methods.  In both cases, the chassis grounds of the generators should be connected.

Without the parallel kit, each generator makes an independent 20A 120V unbonded circuit.  With the parallel kit, you get a 50A 120V receptacle, generally designed for an RV.  The hot, neutral, and ground are paralleled, but it is still unbonded.

Bonding the ground to neutral is part of standard electrical service practice, because without it, a fault to ground won't trip the breaker or GFCI. 

The Honda generators ship without this bond and without GFCI receptacles because the thinking is that in a single-circuit generator, there really isn't another fault path for the current to go anyway.  I.e you can hold the hot wire and stand barefoot in a puddle all you want, but since there's no connection between the earth ground and the current-carrying wires, there's no circuit, whereas if you do have a ground -> neutral bond, now you are depending on the GFCI device to function, and sometimes they fail.

This becomes more complicated when you have multiple fault paths.  Say you have a pinched extension cord that happens to short your neutral wire to the stage which creates a ground -> neutral bond, and you also have a guitar amp with a hot chassis fault - now you're in trouble.

A system with multiple circuits - such as a pair of unrelated generators or multiple circuits from a larger generator can create multiple fault paths as well.

Multiple ground -> neutral bonds are problematic, because effectively you turn the ground wire into a current carrying conductor.  This is fine for the initial bond at the service because the bond needs to be somewhere to close the fault current circuit and you have tied this point to earth with a nice big ground rod driven into the ground, but if you have more than one bond, current can potentially flow on the chassis of the generators relative to earth - in other words you can get shocked touching a generator.

We have been talking about 3 basic setups: Paralleled Hondas, Unparalleled Hondas, and the EU6500/EU7000.  Brief pros and cons:

- Paralleled Honda EU3000is: Provides a 30A 120V receptacle with a pair of EU2000is or a 50A 120V receptacle with a pair of EU3000s.  If you need these larger single circuits, this is your only choice with small generators.  If you don't need these high-current circuits and don't have an external distro to manage it, the parallel kit is arguably not better than just dividing the load between your two generators.  For safest operation, you need to do a ground -> neutral bond external to the generator (best done inside your 30A or 50A distro, IMO), and you need to use external GFCI protection.  A ground rod is a good idea if you're using the G-N bond in your distro, or a critical idea if you're using multiple bonds at the generators.  The parallel kit provides an additional point of vulnerability in that you are using single wire connectors.  If the neutral wire fails or becomes disconnected, you could be in trouble.

- Non-paralleled Honda EU3000is: Each generator provides a 20A 120V circuit with a little generator headroom for peak loads.  If you're just running devices that fit on 20A circuits, this is arguably simpler and better than trying to use the parallel kit and and external distro.  Safest operation requires the generator frames to be bonded with a #10 wire, and each generator to have a ground -> neutral bond (can be accomplished by making a male plug with a jumper between ground and neutral and plugging one of these into each generator).  These generators should be as close together as possible, and a ground rod should be used to ensure that the generator frames stays at the same electrical potential as the earth.  External GFCIs are required.

- Honda EU6500is: Generator provides 2 20A 120V circuits on the panel, or with an external distro can provide 30A 120V/240V.  The significant advantages are a much larger power platform that can handle higher peak loads, and a unified electrical system.  This is much less of a band-aid compared to using multiple generators - with or without the parallel kit.  A ground -> neutral bond is required (can be done using a male L5-30 plug with the G->N jumper), but now this bond is happening only at the current source. External GFCIs are required. 

By the way, if you're using a metal stage, you need to bond your stage to your electrical system ground too.
Title: Re: Generator question
Post by: Art Hays on September 17, 2015, 12:08:07 PM
From the generator schematics I can't see how paralleling two EU2000's is any different from using one EU6500 other than convenience, e.g. capacity issues and how you draw the loads. 

Thanks, Tom.  A very clear summary of all the issues!

I did find some more info on my question above.  If the loads aren't well behaved with regard to power factor then the harmonic currents can kind of circulate between paralleled generators lowering the total output available ('cross currents').

I also found that OSHA requires generators to have a ground-neutral bond on job sites (so there's info on the web about how to modify generators to do this).  But when connecting a generator in a standby application using a transfer switch, say at a home, you don't want to have two bonds since the panel is already bonded.  This may be another reason Honda ships without the ground-neutral bond.
Title: Re: Generator question
Post by: TJ (Tom) Cornish on September 17, 2015, 12:31:48 PM
Thanks, Tom.  A very clear summary of all the issues!

I did find some more info on my question above.  If the loads aren't well behaved with regard to power factor then the harmonic currents can kind of circulate between paralleled generators lowering the total output available ('cross currents').
This is an additional advantage of the EU6500 series if you can run some of your gear at 240v, since this sidesteps the harmonics issue.  Most power amps and powered speakers can be run at 240v. My solution is to use a distro that uses an L14-30 inlet from the generator and provides a 20A 240V L6-20 receptacle and a couple Edison circuits.  I then use a Poor Man's distro like this one http://triktags.com/power.htm to distribute the 240V power via Powercons to amps/powered speakers, which is an acceptable use of the Powercon connector, as long as it's breakered at no more than 20A (this is the importance of the first distro).  The 120V receptacles from the first distro supply stage power and all other 120V needs.

I also found that OSHA requires generators to have a ground-neutral bond on job sites (so there's info on the web about how to modify generators to do this).  But when connecting a generator in a standby application using a transfer switch, say at a home, you don't want to have two bonds since the panel is already bonded.  This may be another reason Honda ships without the ground-neutral bond.
OSHA is another ingredient in the soup, and occasionally conflicts with the NEC.  The Hondas ship unbonded for the reason I mentioned earlier about the presumed safety of an isolated system, as well as for the home backup power application you mention.  I wish they put a selectable G->N bond on the generator, but I suppose that's just another thing to confuse the average user.
Title: Re: Generator question
Post by: g'bye, Dick Rees on September 17, 2015, 12:32:50 PM
Thanks, Tom.  A very clear summary of all the issues!

I did find some more info on my question above.  If the loads aren't well behaved with regard to power factor then the harmonic currents can kind of circulate between paralleled generators lowering the total output available ('cross currents').

I also found that OSHA requires generators to have a ground-neutral bond on job sites (so there's info on the web about how to modify generators to do this).  But when connecting a generator in a standby application using a transfer switch, say at a home, you don't want to have two bonds since the panel is already bonded.  This may be another reason Honda ships without the ground-neutral bond.


All of ths has been covered in depth in the POWER FORUM.  It's worth the search and the read and you won't have to go through it piece by piece again.

Everybody go over there and look it up.
Title: Re: Generator question
Post by: Stephen Kirby on September 17, 2015, 01:35:33 PM
Please don't take this personally-I am sure there are plenty of audio and business principles you could school me on-but this statement shows a basic misunderstanding of grounding and bonding issues and how electrical power works.
Thus the reason I brought up the questions.  I'm trying to translate electronics and EMI stuff into power distribution.  My understanding is that the ability to dissipate energy is more or less the definition of ground.  Where something is isolated from the ability dissipate the energy, there will be a potential between it and something that does.  One reason a ground connection is often called a "drain".  At electronics frequencies, the potential between one drain and another is a major headache.

e.g.

  These generators should be as close together as possible, and a ground rod should be used to ensure that the generator frames stays at the same electrical potential as the earth.

Without that tie to earth, something that is either tied loosely to earth or has a greater ability to dissipate energy like a big metal stage sitting on dirt (not a serious connection but a better drain nonetheless) can develop a potential between it and something with no such reference or drain.  Thus the comment (maybe using the wrong terminology for electrical power) that the generator is floating relative to the stage.  And the concern that there could be a potential between anything connected to the generator's ground or neutral and the stage.

Another example, and maybe something different than my understanding was happening here, some years ago I had a machine (SMT placement machine) that would periodically lose it's mind and crash randomly.  Drove us nuts for a couple months until one day I happened to touch the machine and an output conveyor at the same time and felt a tingle.  I grabbed a meter and measured 40 odd VAC between the two chassis.  The big machine was hardwired into a 3 phase service but the conveyor was just plugged into Edison outlets.  Tracing that back I found that some production worker had inserted an outlet strip so they could plug a fan or something else into it that had the ground pin cut off.  That let the chassis of the conveyor float up to the point where when vibration caused the two frames to touch, the blip into the ground was enough to cause the embedded computer to crash.  I've since made sure to specify plenty of extra Edison outlets on any line in installed and banned plastic outlet strips that workers and supervisors seem to sneak into plants.  And which I've had no end of audio problems with in my music world due to poor ground connections.

There are a lot of folks like me and Debbie running small systems in various situations like the one she describes in the OP who may be overwhelmed by the discussions in the power sub-forum.  Or coming from different disciplines that look at things differently from different experiences.  If I've got this all wet, I'm sure we could all benefit from a basic understanding.
Title: Re: Generator question
Post by: TJ (Tom) Cornish on September 17, 2015, 02:19:08 PM
Stephen, some good thoughts.  I think we tend to forget that electricity is analog, not digital, and as such we end up with a lot of continuums.  In between "broken" and "Working" we have lots of "sort of working" or "sometimes working" situations; and in the safety dimension we have "really dangerous", "somewhat dangerous", "possibly dangerous depending on the circumstances", ...

The case of bonding generators fits this exactly.  In a simple case, the unbonded, non-GFCI single-circuit generator is simpler, less likely to fail, and safer in a single fault situation than a bonded generator. However, that same practice in a more complicated environment quickly becomes less-safe than a bonded setup.

I haven't seen a way to distill down power distribution down to something trivial - it is a knowledge investment just like other audio skills.
Title: Re: Generator question
Post by: Stephen Swaffer on September 17, 2015, 11:50:45 PM

I haven't seen a way to distill down power distribution down to something trivial - it is a knowledge investment just like other audio skills.

However, your earlier post did a good job of distilling down to a simple "connect the dots" procedure when using the Honda generators-as least as far as safety is concerned.

There are plenty of other nuances to learn-such as was mentioned a 20 amp generator circuit may not have the same reserve power for surges as a 20 amp POCO supplied circuit, etc.  Those things you can take time to learn and grow with-but on the safety side if you have to "connect the dots" for a while do it-just don't skip any-even they don't really seem important.

Thus the reason I brought up the questions.  I'm trying to translate electronics and EMI stuff into power distribution.  My understanding is that the ability to dissipate energy is more or less the definition of ground.  Where something is isolated from the ability dissipate the energy, there will be a potential between it and something that does.  One reason a ground connection is often called a "drain".  At electronics frequencies, the potential between one drain and another is a major headache.

e.g.

Without that tie to earth, something that is either tied loosely to earth or has a greater ability to dissipate energy like a big metal stage sitting on dirt (not a serious connection but a better drain nonetheless) can develop a potential between it and something with no such reference or drain.  Thus the comment (maybe using the wrong terminology for electrical power) that the generator is floating relative to the stage.  And the concern that there could be a potential between anything connected to the generator's ground or neutral and the stage.

In power distribution, the "ground" connection or wire is not supposed to have current flowing on it-code prohibits "objectionable" current.  (I realize that is theoritical and there will likely always be minor stray currents.) The "ground"-as in the earth is used for safety-and to dissipate energy from lightning or other major faults.  The ground wires as in equipment grounding conductors in a system are there to provide a path for fault current to trip breakers or blow fuses.

You are correct in saying the generator is floating-it is not referenced to the stage. I guess in my mind, ground is more a point of reference-which is useless unless we intentionally make a connection to that point of reference. To compare with electronics, a similar situation would be if I asked "what is the voltage at point A?"  Meaningless unless I give you a reference point.  Similarly, 2 different PC boards with disconnected commons create issues when trying to determine potential  difference-obviously the situation is "out of control".  By grounding and thus referencing to ground we make fault conditions and corrective actions more predictable.
Title: Re: Generator question
Post by: Stephen Kirby on September 19, 2015, 12:15:59 AM
Thanks Steve.

So the neutral is effectively the "drain" and reference and "ground" is a fault path for anything that goes haywire.?  Therefore I expect that you want to have neutrals commoned at the same point they're tied to a ground point.  So that any return current drains back to the same potential and any fault detection is double referenced to the same point.  Which is how I understand house wiring.
Title: Re: Generator question
Post by: Guy Holt on September 20, 2015, 10:50:56 AM
 
When im in a club, i can run my rig,lighting backline and foh all on 1 20 amp circuit. I did an outdoor show which used a generator to provide power…. As soon as the first note dropped the meter on the regulator dropped as low as it could go. … My questions to the forum are; could the generator have been undersized?

Many good recommendations offered, but no real explanation for what the OP experienced. Clearly the generator was not undersized (at least not in the sense that OP means) for surely a trailer-mounted generator is capable of delivering a single 20A circuit.  And while 14AWG cable is slightly undersized for the OP’s load, 25’ is not long enough of a run to cause the kind of voltage drop he experienced.  The cause of the severe voltage drop as soon as the load kicked in was clearly something else.  Without knowing all the details of his load, I am going to guess the harmonics drawn by some or all of his load was the cause simply because what worked fine on grid power, did not on generated power.

I don’t know about the JBL PRX powered speakers, or the QSC HPR 181 subwoofers, because manufacturers generally don’t specify, but it is very likely that the 12 LED Par64s are not power factor corrected and so draw harmonic currents.  In a recent survey of LED lights that I conducted, all of the LED Pars (like the Chauvet Slim Par Pro below) were not power factor corrected (pfc.) With power factors as low as .45, LED Pars can draw twice the current than a tungsten light of the same wattage and draw considerable harmonic currents. The harmonic currents non-pfc LED lights draw can cause severe voltage waveform distortion in the power supplied by generators while having no effect on the power provided by the grid (To see which LED lights are power factor corrected or not, use this link - http://www.screenlightandgrip.com/html/emailnewsletter_generators.html#anchorHigh Output AC LEDs (http://www.screenlightandgrip.com/html/emailnewsletter_generators.html#anchorHigh Output AC LEDs) - to see some of the results of my tests.)

(http://www.screenlightandgrip.com/images/generators/Chauvet_Slim_Par_Composite.jpg)
The Chauvet Slim Par Pro RGBA has a pf of .61 and Total Harmonic Distortion of 81%

As is evident in the power quality meter reading of the Chauvet Slim Par Pro above, the high peaked pulsed current (lower waveform on the left) drawn by its’ smoothing capacitors is a distorted waveform that does not resemble the sinusoid of AC voltage or the current drawn by an incandescent light. As such, the current drawn includes a number of harmonic currents in addition to the 60hz fundamental (see Fast Fourier Transformation above right).  The accumulative effect of twelve of these lights can cause not only line loss but also cause voltage “flat topping.” If the voltage waveform distortion is severe, it can also cause voltage regulator sensing problems and inaccurate instrument readings, which would explain the problems experienced by the OP.

Let’s look at the line loss component of this problem first. As you can see in the Fast Fourier Transformation of the Chauvet Slim Par Pro above, non-pfc LEDs draw a distorted current waveform that is rich in harmonics. The higher harmonic frequencies create what is known as "skin effect" in cable. Skin effect is a phenomenon where the higher frequencies cause the electrons to flow toward the outer sides of a conductor. Since the flow of the electrons is no longer evenly distributed across the cross sectional diameter of the conductor, more electrons are flowing through less copper and the resistance of the conductor increases. This increase in resistance reduces the ability of the conductor to carry current, resulting in greater voltage drop over shorter distances. In this case, the situation was aggravated by the fact that the cable was undersized for the load to begin with.

(http://www.screenlightandgrip.com/images/generators/skin_effect.jpg)
The area of the cross sectional diameter of a conductor used by DC current (left), Low Frequency AC Current (center), High Frequency AC Currents (right).

But, skin effect alone would not account for the problems the OP experienced. The other contributing factor was probably voltage “flat topping” caused by the high impedance of the industrial generator used.  What causes flat-topped voltage? According to Ohm’s Law current reacts with impedance to cause voltage drop. For example, when encountering the high impedance of an industrial generator, a 3rd harmonic current will produce a voltage drop at a 3rd harmonic voltage. Likewise a 5th harmonic current will produce a voltage drop at a 5th harmonic voltage, etc. Each harmonic current drawn by the non-power factor corrected LED flows through the system impedance, resulting in a voltage drop at that harmonic frequency. In other words, where a distorted current waveform is made up of the fundamental plus one or more harmonic currents, each of these currents flowing into an impedance will according to Ohm’s Law, result in a voltage drop resulting in voltage harmonics appearing at the load bus and distortion of the voltage waveform like that exhibited in the right oscilloscope shot below.

(http://www.screenlightandgrip.com/images/generators/waveform_com_grid-AVR.jpg)
Left: Pkg. of 2-1200 HMI Par w/ non-pfc ballasts & Kino Wall-o-Lite powered by grid power. Right: Same Lighting Pkg. powered by industrial Generator (Honda EX5500) Note different effect that the same non-linear load harmonics have on grid power and power from an industrial generator.

This pattern does not appear in the voltage waveform of the grid power above because of its’ much lower impedance.  Which means that none-linear loads which work fine on utility power, will react entirely different when powered by a generator set. In practice, when you plug non-linear loads like non-pfc  amplifiers, power wedges, and LED lights into a wall outlet you need not be concerned about current harmonics producing voltage distortion. The impedance of the power source is so low, the distortion of the original applied power waveform so small (less than 3%), and the power plant generating capacity so large by comparison to the load, that harmonic currents will not effect the voltage at the load bus.

However, it is an all-together different situation when plugging these same loads into a small portable generator that is not specifically designed to remediate the effects of harmonics. Given the comparatively large sub-transient impedance of industrial generators, and the high THD value of their inherent power waveform (see no load waveforms below), you have a situation where even a small amount of harmonics being fed back into the power stream will result in a large amount of harmonic distortion in its’ voltage.

(http://www.screenlightandgrip.com/images/generators/waveform_com_grid-AVR_no-lo.jpg)
Left: Original Grid Waveform w/no load & low THD (>3%)
Right: Original waveform of an industrial generator (Honda EX5500)  w/ no-load & high THD (@17%)

The rudimentary AVR systems used in portable industrial generators are especially ill equipped to deal with the voltage distortion caused by the harmonics drawn by LED lights because the harmonic currents they draw create flux in the armature coils of the generator’s stator that reacts additively with the generator’s exciter flux in the field poles of the generator’s rotor to increase saturation and produce a higher terminal voltage than called for a given load.  Consequently, the AVR system responds erroneously to control voltage by reducing excitation.  Because an AVR system is a closed-loop control system, as the voltage is incorrectly lowered, based on the distorted information, it is then even more incorrect.  The end result is that the regulator goes to its minimum excitation capability and the voltage output drops severely.

The impedance of a generator is not an easily known quantity. Depending on its’ size and design, the impedance of a generator will be 5 to 100 times that of a utility transformer and it will change as the load changes. But where the OP was using an industrial generator, the internal reactance would have been sufficient to cause appreciable voltage distortion and consequently a severe voltage drop on the generator output.

We can now also understand why a Honda inverter generator would have served the OP better.  As demonstrated above harmonic currents react with impedance to cause voltage waveform distortion.  The magnitude of the voltage waveform distortion is a function of the source impedance. Which means that the generator with the lowest internal reactance to an instantaneous current change at a given load will typically have the lowest value of total harmonic distortion under nonlinear load conditions. This is one of the great benefits to using inverter generators over industrial generators: inverter generators have much lower internal reactance and so they are less prone to voltage waveform distortion caused by the harmonic currents drawn by switching power supplies.

(http://www.screenlightandgrip.com/images/generators/waveform_elec_ballast.jpg)
Left: A 1200W non-linear Load powered by Grid Power. Center: A 1200W non-linear Load powered by an industrial generator. Right: A 1200W non-linear Load powered by Inverter Power.

As can be seen in the oscilloscope shots above, inverter generators are less prone to voltage waveform distortion because, as mentioned previously, the inverters completely process the raw power generated by its alternator (converting it to DC before converting it back to AC) – making the AC power it generates completely independent of the engine. In fact, its’ microprocessor controller can vary the engine speed without affecting the voltage or frequency of the power the inverter module puts out. Now that the internal reactance of the engine is separated from the power output, harmonic currents encounter very little impedance; and, as is evident in the oscilloscope shot above right, there is considerably less voltage distortion at the load bus of inverter generators than there are conventional generators. The net benefit is that non-linear loads, like the switching power supplies of non-pfc equipment, do not adversely affect the power of inverter generators as they do the power of industrial generators. Which means that non-linear loads will operate more reliably on inverter generators.

For a more detailed explanation of what causes voltage waveform distortion and how to mitigate it, see my white paper on the use of portable generators in motion picture production that is available at http://www.screenlightandgrip.com/html/emailnewsletter_generators.html. (http://www.screenlightandgrip.com/html/emailnewsletter_generators.html.)

Guy Holt, Gaffer
ScreenLight & Grip
www.screenlightandgrip.com
Title: Re: Generator question
Post by: Stephen Swaffer on September 20, 2015, 03:58:19 PM
Guys response could be the answer-another possibility is a bad (corroded) connection/loose wire internal to the genny or anywhere prior to the Furman with a high resistance.  This would mimic a genny with a high internal impedance. It would also allow the voltage to be just fine under no load-but drive it lower and lower with an increase in load.

We are all familiar with the car battery that lights the dome light but everything dies when you hit the starter-could be a dead battery (inadequate genny) or it could be an oxidized battery terminal.

Just something else to look for and troubleshoot that might be fixable in the hour or 2 immediately before a gig when there is not enough time to find another genny.
Title: Re: Generator question
Post by: RYAN LOUDMUSIC JENKINS on September 21, 2015, 08:17:43 AM
None of us were there and no one really knows but I think I know the answer and I didn't see any other mentions of it.  I use generators on nearly 90% of my events.  Almost always diesel generators.  In our area we see mostly MQ Power and Airman generators.

The older MQ Power generators had a throttle control knob that you have to pull on and twist to put the throttle control on correctly.  These throttle control features went away several years ago but I still get generators with them every year.

The generators will show 120/240 +/- volts with the throttle control off but as soon as there is a load, the voltage drops significantly.

There's your most likely answer since you don't really have details for us.
Title: Re: Generator question
Post by: Guy Holt on September 21, 2015, 06:25:14 PM
There seems to be some outdated information as well as questions in this thread about the paralleling of the Honda generators.  For instance,

- Honda EU6500is: Generator provides 2 20A 120V circuits on the panel, or with an external distro can provide 30A 120V/240V

Not exactly, out of the box a EU6500 or EU7000 has a continuous load rating (loads lasting more than a half hour) of 5500W and a peak load rating of 6500W and 7000W respectively.  Since in our case, loads run for more than a half hour,  the 30A 240V receptacle on the generator should only provide 23A per leg for an extended period of time.

- Paralleled Honda EU3000is: Provides a 30A 120V receptacle with a pair of EU2000is or a 50A 120V receptacle with a pair of EU3000s.  If you need these larger single circuits, this is your only choice with small generators.


Not exactly, there are other choices.  A 60A Transformer/Distro will step-down the 240V output of an unmodified Honda  EU6500 or EU7000 to a single 46A/120V circuit (see above.)  You can also parallel two EU6500s or EU7000s and use a Transformer/Distro to create a single 100A/120V circuit.

I incorrectly said one could connect two 110v inverter generators and have the option to get 220v (each running 180 deg out of phase from the other). They don't do this- paralleling always connects the two outputs together so they have to be in phase.

Unless you were paralleling two single-phase generators like the EU6500 or EU7000, the result of which is two legs running 180 degrees of phase of one another.

The parallel kits will run the master unit low on fuel before the second unit as they will be loaded in series rather than parallel.  This shortens your run time.
Seems a big disadvantage if they don't each supply 50% to the load when paralleled.

Not only will the generator that picks up the majority of the load run out of fuel quicker, but if the system continues to be loaded, it will also trip it’s breaker before the more lightly loaded generator.  The net result is that you can never fully utilize the generating capacity of the system. For this reason we have engineered a load sharing control into our paralleling control for the Honda EU6500s and EU7000s. 

… don't know how they work their magic, and especially in terms of grounding.  The manual says they have a ground terminal, which connects all metal stuff but is not connected to the generator output.  So you would think that step one is join the frame ground terminals together, "just in case.

The ground terminal does in fact connect all the metal parts of  the generator to the ground pin of the output receptacle.

I tried to learn how paralleling works but couldn't find anything technical

My white paper on the use of portable generators in motion picture production does include a lot of technical information on the operation of the Honda EU6500s and EU7000s in parallel.  It is available at http://www.screenlightandgrip.com/html/emailnewsletter_generators.html#anchorParallelingEU6500s (http://www.screenlightandgrip.com/html/emailnewsletter_generators.html#anchorParallelingEU6500s)

Guy Holt, Gaffer
ScreenLight & Grip
www.screenlightandgrip.com
Title: Re: Generator question
Post by: TJ (Tom) Cornish on September 21, 2015, 08:37:27 PM
There seems to be some outdated information as well as questions in this thread about the paralleling of the Honda generators.  For instance,
Quote from: TJ
- Honda EU6500is: Generator provides 2 20A 120V circuits on the panel, or with an external distro can provide 30A 120V/240V
Not exactly, out of the box a EU6500 or EU7000 has a continuous load rating (loads lasting more than a half hour) of 5500W and a peak load rating of 6500W and 7000W respectively.  Since in our case, loads run for more than a half hour,  the 30A 240V receptacle on the generator should only provide 23A per leg for an extended period of time.
 
Guy, with respect, sometimes I wonder if you are trying to be helpful or just pushing your transformer product.  This is an audio forum, and though sometimes loads do contain a lighting component, the vast majority - and I would venture nearly all for a show that would fit on something the size of an EU6500 would be audio loads.  These are dominated by peak draw which is measured in fractions of a second rather than 30 minutes.  It would be great if you would take some time to understand how we work, and not just assume everything is a lighting load.

Quote from: TJ
- Paralleled Honda EU3000is: Provides a 30A 120V receptacle with a pair of EU2000is or a 50A 120V receptacle with a pair of EU3000s.  If you need these larger single circuits, this is your only choice with small generators.
Not exactly, there are other choices.  A 60A Transformer/Distro will step-down the 240V output of an unmodified Honda  EU6500 or EU7000 to a single 46A/120V circuit (see above.)  You can also parallel two EU6500s or EU7000s and use a Transformer/Distro to create a single 100A/120V circuit.
Do you sell a product designed for a pair of EU3000is generators? That's what I was talking about here, and my info comes right from the generator manual.

A 60A distro/transformer deal is fine for a single 120V light source load, which is, I understand, your primary application.  For the typical audio application, running the gear at 240V directly from the generator is even better yet.  It sidesteps your neutral harmonics issue, and the amps are happier, too, not to mention avoiding procuring and hauling another big chunk of iron that will raise inspector's eyebrows.

Unless you were paralleling two single-phase generators like the EU6500 or EU7000, the result of which is two legs running 180 degrees of phase of one another.

Not only will the generator that picks up the majority of the load run out of fuel quicker, but if the system continues to be loaded, it will also trip it’s breaker before the more lightly loaded generator.  The net result is that you can never fully utilize the generating capacity of the system. For this reason we have engineered a load sharing control into our paralleling control for the Honda EU6500s and EU7000s. 

The ground terminal does in fact connect all the metal parts of  the generator to the ground pin of the output receptacle.

My white paper on the use of portable generators in motion picture production does include a lot of technical information on the operation of the Honda EU6500s and EU7000s in parallel.  It is available at http://www.screenlightandgrip.com/html/emailnewsletter_generators.html#anchorParallelingEU6500s (http://www.screenlightandgrip.com/html/emailnewsletter_generators.html#anchorParallelingEU6500s)

Guy Holt, Gaffer
ScreenLight & Grip
www.screenlightandgrip.com
Title: Re: Generator question
Post by: Guy Holt on September 22, 2015, 11:28:09 AM
I wonder if you are trying to be helpful or just pushing your transformer product.  This is an audio forum, and though sometimes loads do contain a lighting component, the vast majority - and I would venture nearly all for a show that would fit on something the size of an EU6500 would be audio loads. 
 

Just trying to be helpful by correcting a, good intentioned I am sure, incorrect statement.  Though you may not have meant it this way, when you reference the larger 120V circuits that can be obtained by paralleling both EU2000s and EU3000s, you are no longer just talking about paralleling EU3000s , but paralleling small generators in general.  In that context your statement that “this is your only choice with small generators” is false since it is now possible to parallel EU6500s and EU7000s.  Since readers look to this forum for the final word on production technique, I felt it would be a disservice to the readers of this forum to not inform them of new options.  And since the OP was in fact operating lights on the generator, as do many users of small generators in this forum, I think it is relevant to point out the different ratings for peak load verses continuous load for these generators.  Again, it would be a disservice to the OP and other readers to lead them to believe the EU6500/7000 provides 30Amps per leg on the 240V receptacle straight out of the box when in fact it does not.

A 60A distro/transformer deal is fine for a single 120V light source load, which is, I understand, your primary application.  For the typical audio application, running the gear at 240V directly from the generator is even better yet.  It sidesteps your neutral harmonics issue, and the amps are happier, too, not to mention avoiding procuring and hauling another big chunk of iron that will raise inspector's eyebrows.

While operating gear at 240V will minimize neutral harmonics issues, it does not eliminate the voltage waveform distortion described in my previous post.  Better still would be to use only power factor corrected equipment that does not draw harmonic currents in the first place. Not only will equipment operate more reliably on the cleaner power, but you will be able to operate appreciably more equipment on a small generator because power factor corrected equipment is more efficient and you do not have to oversize the generator, i.e. reduce the load, in order to mitigate the adverse effects that harmonic currents can have on small generators.

Since you have now begun to debate the merits of using transformers with small portable generators, I don’t think I can be faulted for responding with what I see to be the advantages to using them in pro audio productions regardless whether your loads are power factor corrected or not.  I can think of several good reasons to operating the typical production package on a single large circuit derived from a step-down transformer rather than on a 240V splitter box consisting of 240V and 120V receptacles.  First, since there are some loads that can’t operate at 240V, balancing your 120V loads over the two legs of a portable generator is a concern. If you power your amps at 120V,  you don’t have to worry about balancing any of your loads  because the transformer does it automatically.  No matter what branch circuit you plug a 120V load into it is split evenly over the primary of the transformer so that the generator only sees a perfectly balanced load.  Second, the taps on the transformer can be used to compensate for line-loss on a long cable run and voltage drop on the generator under load, which small portable generators are very prone to.   Third, the ground/neutral bond on the secondary side of a transformer, and a ground rod, will ensure that downstream GFCI devices will operate reliably which they don’t do on the floating neutral systems of the Honda EU generators (see my IATSE Local 481 workshop on ground fault protection for more details. The workshop is available for free online at http://www.screenlightandgrip.com/html/481_GFCI_Workshop.html (http://www.screenlightandgrip.com/html/481_GFCI_Workshop.html).) Finally, I would not be concerned about a small portable transformer raising the eyebrows of an Inspector – they are quite familiar with them from construction sites.

Guy Holt, Gaffer
ScreenLight & Grip
www.screenlightandgrip.com
Title: Re: Generator question
Post by: TJ (Tom) Cornish on September 22, 2015, 12:07:56 PM
Just trying to be helpful by correcting a, good intentioned I am sure, incorrect statement.  Though you may not have meant it this way, when you reference the larger 120V circuits that can be obtained by paralleling both EU2000s and EU3000s, you are no longer just talking about paralleling EU3000s , but paralleling small generators in general.  In that context your statement that “this is your only choice with small generators” is false since it is now possible to parallel EU6500s and EU7000s.
My statement wasn't incorrect; you're redefining "small generators" to be something other than what my reply - and the preceding couple of pages of posts were about - the EU3000.  This thread started in the Lab Lounge, where an EU6500 is arguably a "large generator" - especially as the thread progressed.
Since readers look to this forum for the final word on production technique, I felt it would be a disservice to the readers of this forum to not inform them of new options.  And since the OP was in fact operating lights on the generator, as do many users of small generators in this forum, I think it is relevant to point out the different ratings for peak load verses continuous load for these generators.  Again, it would be a disservice to the OP and other readers to lead them to believe the EU6500/7000 provides 30Amps per leg on the 240V receptacle straight out of the box when in fact it does not.

While operating gear at 240V will minimize neutral harmonics issues, it does not eliminate the voltage waveform distortion described in my previous post.  Better still would be to use only power factor corrected equipment that does not draw harmonic currents in the first place. Not only will equipment operate more reliably on the cleaner power, but you will be able to operate appreciably more equipment on a small generator because power factor corrected equipment is more efficient and you do not have to oversize the generator, i.e. reduce the load, in order to mitigate the adverse effects that harmonic currents can have on small generators.

Since you have now begun to debate the merits of using transformers with small portable generators, I don’t think I can be faulted for responding with what I see to be the advantages to using them in pro audio productions regardless whether your loads are power factor corrected or not.  I can think of several good reasons to operating the typical production package on a single large circuit derived from a step-down transformer rather than on a 240V splitter box consisting of 240V and 120V receptacles.  First, since there are some loads that can’t operate at 240V, balancing your 120V loads over the two legs of a portable generator is a concern. If you power your amps at 120V,  you don’t have to worry about balancing any of your loads  because the transformer does it automatically.  No matter what branch circuit you plug a 120V load into it is split evenly over the primary of the transformer so that the generator only sees a perfectly balanced load.  Second, the taps on the transformer can be used to compensate for line-loss on a long cable run and voltage drop on the generator under load, which small portable generators are very prone to.   Third, the ground/neutral bond on the secondary side of a transformer, and a ground rod, will ensure that downstream GFCI devices will operate reliably which they don’t do on the floating neutral systems of the Honda EU generators (see my IATSE Local 481 workshop on ground fault protection for more details. The workshop is available for free online at http://www.screenlightandgrip.com/html/481_GFCI_Workshop.html (http://www.screenlightandgrip.com/html/481_GFCI_Workshop.html).) Finally, I would not be concerned about a small portable transformer raising the eyebrows of an Inspector – they are quite familiar with them from construction sites.

Guy Holt, Gaffer
ScreenLight & Grip
www.screenlightandgrip.com
We will have to agree to disagree on the relative merits of a big transformer and inspector's reactions vs. other distribution methods.  I stand by my assertion that a film set is significantly different from a lounge-level sound gig with a few LED par cans. 

If you really want to be helpful, how about condensing or dividing your epic-length white paper into something readable with relevant information for our industry geared for a non-EE reader?  The typical reader of this forum section would get about 3 paragraphs in before glossing over and missing your message.
Title: Re: Generator question
Post by: Guy Holt on September 22, 2015, 01:18:18 PM
My understanding is that the ability to dissipate energy is more or less the definition of ground… reason a ground connection is often called a "drain"… Without that tie to earth, something that is either tied loosely to earth or has a greater ability to dissipate energy like a big metal stage sitting on dirt (not a serious connection but a better drain nonetheless) can develop a potential between it and something with no such reference or drain. … If I've got this all wet, I'm sure we could all benefit from a basic understanding.

I may be mistaken, but this sounds vaguely like the erroneous “Sump Theory of Ground.” According to this theory "electricity wants to go to ground" because the earth is some kind of giant reservoir of electro-magnetic charge from which all electricity comes and to which it must ultimately return and dissipate. This is a commonly held fallacy and can even be found in electrical safety training videos and books published about electrical wiring.  As is evident by the fact that ground faults pose no threat in single circuit floating neutral generators demonstrates clearly the fallacy of this theory.

(http://www.screenlightandgrip.com/images/generators/SB_Sump_Theory.jpg)

That there is no ground leak in this case clearly demonstrates that electricity wants to return to its source and nowhere else – especially not a supposed giant sump that is planet earth.  Electricity is attracted only to the singular magnetic field, in the core of a transformer or the rotors of a generator, from which it was created. The two low impedance conductors (the Neutral & EGC) that are designed to carry it safely are the preferred rout it takes. Whenever current goes to earth ground, or any other ground loop, it is only because it offers an alternate means to return to its' source.  In fact, according to the NEC, earth ground is not an acceptable path for fault current. I hope this has been helpful.

Guy Holt,
ScreenLight & Grip,
www.screenlightandgrip.com
Title: Re: Generator question
Post by: Stephen Swaffer on September 22, 2015, 09:06:45 PM




Since you have now begun to debate the merits of using transformers with small portable generators, I don’t think I can be faulted for responding with what I see to be the advantages to using them in pro audio productions regardless whether your loads are power factor corrected or not.  I can think of several good reasons to operating the typical production package on a single large circuit derived from a step-down transformer rather than on a 240V splitter box consisting of 240V and 120V receptacles.  First, since there are some loads that can’t operate at 240V, balancing your 120V loads over the two legs of a portable generator is a concern. If you power your amps at 120V,  you don’t have to worry about balancing any of your loads  because the transformer does it automatically.  No matter what branch circuit you plug a 120V load into it is split evenly over the primary of the transformer so that the generator only sees a perfectly balanced load.  Second, the taps on the transformer can be used to compensate for line-loss on a long cable run and voltage drop on the generator under load, which small portable generators are very prone to.   Third, the ground/neutral bond on the secondary side of a transformer, and a ground rod, will ensure that downstream GFCI devices will operate reliably which they don’t do on the floating neutral systems of the Honda EU generators (see my IATSE Local 481 workshop on ground fault protection for more details. The workshop is available for free online at http://www.screenlightandgrip.com/html/481_GFCI_Workshop.html (http://www.screenlightandgrip.com/html/481_GFCI_Workshop.html).) Finally, I would not be concerned about a small portable transformer raising the eyebrows of an Inspector – they are quite familiar with them from construction sites.


Running all of your loads on a single 120 V circuit doubles your voltage drop compared to running the same load on a 240 volt circuit.  Of course, a 120/240 volt circuit requires an extra wire.  So your pro's/con's would be to compare cost of 3 wire vs 4 wire vs cost of transformer.  Yes you can add a transformer at the end of the run-but that adds complexity to distribution plus potential issues with getting a ground rod vs with a genny typically parked outside away from production.  All trade-offs to consider.

If the generator has voltage drop under load, transformer taps would work well for a steady load-under a dynamic load such as audio, the voltage would rise, perhaps to unacceptable levels when the generator was lightly loaded-making transformer taps a less than ideal solution.  The longer(higher impedance) your run, the greater your variation as the load varies.

As for the floating neutral-it is my understanding that can be fixed with an appropriate bonding jumper.  I simple low cost solution.

I am not trying to gang up on you-but I agree that presenting your solution as a "one size fits all" magic bullet is unrealistic.  It certainly has some positives.  Whether or not the cost vs benefit makes sense, I am not sure of yet.
Title: Re: Generator question
Post by: Jamin Lynch on September 23, 2015, 09:45:06 AM
I'll bet by now the OP and most of the Lab Lounge folks are scratching their heads and are totally confused.

Let's say I have a small outdoor event for 300-500 max. I have 2 PRX subs and 1 PRX top per side, 4 PRX monitors and 8 LED light fixtures. I'll also need stage power for the band and for FOH. The stage is a small portable stage provided by the event people.

I have a brand new Honda EU6500. What do I need to do to make sure everyone is safe and I won't have any other power issues? Can I just plug and play?
Title: Re: Generator question
Post by: TJ (Tom) Cornish on September 23, 2015, 09:58:25 AM
I'll bet by now the OP and most of the Lab Lounge folks are scratching their heads and are totally confused.

Let's say I have a small outdoor event for 300-500 max. I have 2 PRX subs and 1 PRX top per side, 4 PRX monitors and 8 LED light fixtures. I'll also need stage power for the band and for FOH. The stage is a small portable stage provided by the event people.

I have a brand new Honda EU6500. What do I need to do to make sure everyone is safe and I won't have any other power issues? Can I just plug and play?
Almost: 

- Buy a male L5-30 plug, jumper the ground and neutral conductors together using a very short piece of #10 wire inside the plug, insert into the L5-30 receptacle on the generator.  This bonds the ground and neutral, which ensures GFCI devices and circuit breakers will work as intended.

- Get a 2' piece of grounding rod, a clamp, and a short piece of green stranded #10 wire.  Pound ground rod in ground (depending on the area, you may need to have the utility locator out to make sure you're not going to hit anything with your ground rod), or attach #10 wire to existing unpainted metal - bike rack, water hydrant, etc.  Attach the other end to the ground terminal on the generator.  If the stage is metal, you should really find a way to bond the stage to your generator ground, too.

- Set generator to "120V Only" mode.

- Get two inline GFCI devices like these: http://www.amazon.com/TRC-26020008-6-Shockshield-Protected-3-Outlets/dp/B000HHQIK2 and plug them into the two NEMA 5-20 receptacles on the generator.

- Divide the load between the two circuits.  I would probably put the mains and subs on one circuit and the monitors, lights, and stage power on the other.


For a somewhat larger system you might need to be a little more careful and creative, but for your example system, the above is more than adequate, doesn't require modifying the generator, and provides the best balance of safety vs. hassle.  No 200lb transformer is required.
Title: Re: Generator question
Post by: Jamin Lynch on September 23, 2015, 12:52:48 PM
Almost: 

- Buy a male L5-30 plug, jumper the ground and neutral conductors together using a very short piece of #10 wire inside the plug, insert into the L5-30 receptacle on the generator.  This bonds the ground and neutral, which ensures GFCI devices and circuit breakers will work as intended.

- Get a 2' piece of grounding rod, a clamp, and a short piece of green stranded #10 wire.  Pound ground rod in ground (depending on the area, you may need to have the utility locator out to make sure you're not going to hit anything with your ground rod), or attach #10 wire to existing unpainted metal - bike rack, water hydrant, etc.  Attach the other end to the ground terminal on the generator.  If the stage is metal, you should really find a way to bond the stage to your generator ground, too.

- Set generator to "120V Only" mode.

- Get two inline GFCI devices like these: http://www.amazon.com/TRC-26020008-6-Shockshield-Protected-3-Outlets/dp/B000HHQIK2 and plug them into the two NEMA 5-20 receptacles on the generator.

- Divide the load between the two circuits.  I would probably put the mains and subs on one circuit and the monitors, lights, and stage power on the other.


For a somewhat larger system you might need to be a little more careful and creative, but for your example system, the above is more than adequate, doesn't require modifying the generator, and provides the best balance of safety vs. hassle.  No 200lb transformer is required.

Not doubting what you are saying at all.

I've never seen anybody do that before in a similar situation.
Title: Re: Generator question
Post by: Stephen Kirby on September 23, 2015, 01:05:14 PM
Tom, is there a need to calculate wire size to the stage?  It's not a voltage drop issue but is there an impedance issue?  Again trying to relate Guy's points to higher frequency but much lower power electronic applications.  My initial guess would be that as long as it is sufficient to carry the fault current which wouldn't be any greater than what is on the supply side.  But it seems things change in high power applications.

Planning ahead for next summer when I'll have another trailer stage in the dirt.  No genny, it's run off 150' of 6/4 and a CA plug on a nearby building.  Figuring that I should connect my distro chassis to the stage just to make sure they're at the same potential.
Title: Re: Generator question
Post by: Mike Sokol on September 23, 2015, 01:46:34 PM
Almost: 

- Buy a male L5-30 plug, jumper the ground and neutral conductors together using a very short piece of #10 wire inside the plug, insert into the L5-30 receptacle on the generator.  This bonds the ground and neutral, which ensures GFCI devices and circuit breakers will work as intended.

- Get a 2' piece of grounding rod, a clamp, and a short piece of green stranded #10 wire.  Pound ground rod in ground (depending on the area, you may need to have the utility locator out to make sure you're not going to hit anything with your ground rod), or attach #10 wire to existing unpainted metal - bike rack, water hydrant, etc.  Attach the other end to the ground terminal on the generator.  If the stage is metal, you should really find a way to bond the stage to your generator ground, too.

- Set generator to "120V Only" mode.

- Get two inline GFCI devices like these: http://www.amazon.com/TRC-26020008-6-Shockshield-Protected-3-Outlets/dp/B000HHQIK2 and plug them into the two NEMA 5-20 receptacles on the generator.

- Divide the load between the two circuits.  I would probably put the mains and subs on one circuit and the monitors, lights, and stage power on the other.


For a somewhat larger system you might need to be a little more careful and creative, but for your example system, the above is more than adequate, doesn't require modifying the generator, and provides the best balance of safety vs. hassle.  No 200lb transformer is required.

Yes, that covers the basics.

First: Make sure your generator's Neutral is Bonded to its chassis "Ground". The easiest way to test to see if your generator already has a Bonded Neutral is with a 3-light outlet tester. Here's a video I did about this for the RV industry. If you're using a Honda or Yamaha 2KW or 3KW generator, then you KNOW it has a floating neutral. The easiest way to bond the neutral on one of these small/portable inverter generators is with a plug that has the neutral screw connected to the ground screw with a short length of heavy wire. And yes, if you have a metal stage. you'll want to bond that to the generator frame as well. https://www.youtube.com/watch?v=M-bTLdMjuqU

Second: Earth-ground your generator's chassis via its "ground" lug. I usually use at least two ground rods 4 ft long if there's no chance of hitting anything underground, but a pair of 2 ft ground rods should suffice as long as you're in moist soil. I usually dump a gallon a water around this temporary ground rod just for giggles. Yes, you could pee on it to decrease the ground impedance, but don't most people think we're animals already? So stick to a few jugs of water.

Third: Provide GFCI protection for the backline power. Inline GFCI cords work well, or you can have your stage distro wired with GFCI receptacles. Use individual GFCI protectors on the ends of the distro, rather than a single GFCI feeding a lot of gear. Ground fault currents are additive and can cause nuisance trips, so far better to use separate GFCI's for front-line and back-line power. That way one leaky old fender amp won't bring down the entire stage power system. And use heavy extension cords for long runs. So 12-gauge wire on a 15-amp circuit may not be required by code, but it will make for a stiffer supply that won't droop under load. I use 10-gauge cords for long runs of 20-amp circuits, and that can reduce voltage drop by 30% or so. 

Fourth: Don't allow musicians to use stage amps with broken off ground plugs on their power or extension cords. Instead, use the proper DI box with a pin-1 ground lift to stop hums and buzzes.

Fifth: Be extra safe and use a NCVT (Non Contact Voltage Tester) such as a Fluke VoltAlert or Klein NCVT-1 to check mics and instruments for any significant voltage above earth potential. (A standard 90 to 1,000 volt NCVT will trigger around 40 volts when held close to anything with a few square inches of surface area) The first time an NCVT lights up when you point it at a bass player's amp will amaze you. BTW: I've had musicians cut the green EGC/Ground wire inside of the chassis of their amplifier, so don't trust a ground plug on a stage amp 100%.

Sixth: Take all reports of feeling a shock seriously. Shocks should NEVER happen on a properly powered and grounded stage. If someone reports feeling a shock, get out your voltmeter and find out why. The life you save could be your own.
Title: Re: Generator question
Post by: TJ (Tom) Cornish on September 23, 2015, 01:53:12 PM
Not doubting what you are saying at all.

I've never seen anybody do that before in a similar situation.
Jamin, this world is unfortunately murky due to two different typical uses for generators such as the EU series: home backup power and portable power.  If Honda made a bonded generator with GFCI receptacles on the frame, it would be plug and go (plus the ground rod).  Unfortunately Honda hasn't done this, and their current products - the new EU7000 included - are more geared toward the home backup application where a second ground -> neutral bond would be detrimental, and the belief that an unbonded system offers some isolation benefits.

Electrical safety is a continuum.  I believe what I have proposed is the safest method for use with the EU6500 as it accounts for nearly all electrical failure modes with minimal effort and expense, and does not require modifying the generator, so can be used with rented equipment.  I'm very confident that lots of people use EU6500s by just plugging and going - that is Honda's intent with the product after all; however there are demonstrable holes in that plan, depending on what else is wrong.
Title: Re: Generator question
Post by: TJ (Tom) Cornish on September 23, 2015, 02:01:00 PM
Tom, is there a need to calculate wire size to the stage?  It's not a voltage drop issue but is there an impedance issue?  Again trying to relate Guy's points to higher frequency but much lower power electronic applications.  My initial guess would be that as long as it is sufficient to carry the fault current which wouldn't be any greater than what is on the supply side.  But it seems things change in high power applications.

Planning ahead for next summer when I'll have another trailer stage in the dirt.  No genny, it's run off 150' of 6/4 and a CA plug on a nearby building.  Figuring that I should connect my distro chassis to the stage just to make sure they're at the same potential.
I have not researched this issue specifically so I reserve the right to be corrected, but as long as the ground connection has a sufficiently low impedance to trip the largest breaker in use, you will have covered the general intent of the ground fault path.  This should be roughly parity with your supply wiring - i.e. if #12 wire offers an acceptable voltage drop for the distance, a #12 ground wire should be OK too.

If you're using GFCIs for all stage power like you should be, any connection at all should be sufficient to exceed the 5mA trip current of a GFCI device; and this is where the real safety benefits come from.
Title: Re: Generator question
Post by: Mike Sokol on September 23, 2015, 02:15:51 PM
I have not researched this issue specifically so I reserve the right to be corrected, but as long as the ground connection has a sufficiently low impedance to trip the largest breaker in use, you will have covered the general intent of the ground fault path.  This should be roughly parity with your supply wiring - i.e. if #12 wire offers an acceptable voltage drop for the distance, a #12 ground wire should be OK too.
To be accurate, you're not talking about the earth ground connection, which will typically be around 25 ohms or even higher in dry/sandy soil. You're referring to the EGC (Equipment Grounding Conductor) which must have a low-impedance path back to the power source Ground-Neutral bonding point. Note that without a Ground-Nuetral bond there's no path for the GFCI to get its imbalance current, and without an earth ground connected to this G-N bonding point, the GFCI won't trip if you're in the fault path. However, in that case you probably won't be shocked, you'll just raise the potential of your local ground plane to above earth potential. Not a good thing...
Title: Re: Generator question
Post by: TJ (Tom) Cornish on September 23, 2015, 02:31:15 PM
To be accurate, you're not talking about the earth ground connection, which will typically be around 25 ohms or even higher in dry/sandy soil. You're referring to the EGC (Equipment Grounding Conductor) which must have a low-impedance path back to the power source Ground-Neutral bonding point. Note that without a Ground-Nuetral bond there's no path for the GFCI to get its imbalance current, and without an earth ground connected to this G-N bonding point, the GFCI won't trip if you're in the fault path. However, in that case you probably won't be shocked, you'll just raise the potential of your local ground plane to above earth potential. Not a good thing...
Correct - talking about the ground wire between the distro and the stage and not the dirt. 
Title: Re: Generator question
Post by: Guy Holt on September 23, 2015, 02:33:14 PM
..the above is more than adequate, doesn't require modifying the generator, and provides the best balance of safety vs. hassle.

Since when is it permissible to trade off safety for convenience? Safety always comes first.  Here are a few of the things an electrical inspector will have issues with how TJ has traded off safety for convenience.

Almost: 

- Buy a male L5-30 plug, jumper the ground and neutral conductors together using a very short piece of #10 wire inside the plug, insert into the L5-30 receptacle on the generator.  This bonds the ground and neutral, which ensures GFCI devices and circuit breakers will work as intended.

- Get a 2' piece of grounding rod, a clamp, and a short piece of green stranded #10 wire.  Pound ground rod in ground (depending on the area, you may need to have the utility locator out to make sure you're not going to hit anything with your ground rod), or attach #10 wire to existing unpainted metal - bike rack, water hydrant, etc.  Attach the other end to the ground terminal on the generator.  If the stage is metal, you should really find a way to bond the stage to your generator ground, too.
 

According to Article 250.4 (5) "Effective Ground-Fault Current Path," of our National Electrical Code (NEC) requires that the grounding system create "a permanent, low-impedance circuit capable of safely carrying the maximum ground-fault current likely to be imposed on it...." The operative words here are “permanent”, “low-impedance”, and “capable.”  What TJ is suggesting does not meet this definition.

“permanent”: Code compliant bonding of the Neutral of a portable generator to its' frame is not as simple as putting an external jumper between the ground and neutral of an open receptacle as TJ suggests here. A twist-lock plug end that can be mistakenly removed or not fully engaged if not twisted does not meet the definition of permanent.  I have had electrical inspectors kick my ground clamps to make sure that they are permanent.

 “low-impedance”: The prescribed impedance of Earth Ground according to the NEC is 25 Ohms.  It usually takes a 10’ rod, and sometimes two, to get 25 Ohms to ground. It is highly unlikely that TJ’s 2’ rod will provide a code compliant ground.

“capable”: Jumping between the ground and neutral of an open receptacle as TJ suggests here will not likely meet the Code requirement of  "capable of safely carrying the maximum ground-fault current likely to be imposed on it” because  it is not a ‘listed” piece of equipment for that purpose.

(http://www.screenlightandgrip.com/images/generators/SB_GF_Neutral_Bond.jpg)

In open frame models, like the ES6500, you can simply add a Neutral Bond jumper from one of the generator winding leads to the frame (as pictured above.) In an EU series inverter generator, bonding the Neutral to Ground requires removing the main panel and inverter module to get behind the breakers, switches, sockets etc. - not easily done or undone. According to the Honda Service Bulletins, it should only be done by a qualified Honda service technician.

(http://www.screenlightandgrip.com/images/generators/SB_2Fault240V_Exposure.jpg)

The Neutral/Ground bond in a generator is not something to be taken lightly because in a double fault situation like that illustrated above, the two faults create a 240V exposure plus a current path resulting in Electrocution. For this reason it is critical that GFCIs be used effectively and that they operate reliably.  What TJ proposes below is not the most effective use of GFCIs under the circumstances. Mike has partially addressed why in his post above.

Get two inline GFCI devices like these: http://www.amazon.com/TRC-26020008-6-Shockshield-Protected-3-Outlets/dp/B000HHQIK2 and plug them into the two NEMA 5-20 receptacles on the generator.

No 200lb transformer is required.

For the record, a 7.5kVA transformer which is sufficient for a 60A circuit does not weigh 200lbs.

Guy Holt, Gaffer
ScreenLight & Grip
www.screenlightandgrip.com
Title: Re: Generator question
Post by: TJ (Tom) Cornish on September 23, 2015, 02:55:53 PM
Since when is it permissible to trade off safety for convenience? Safety always comes first.  Here are a few of the things an electrical inspector will have issues with how TJ has traded off safety for convenience.

According to Article 250.4 (5) "Effective Ground-Fault Current Path," of our National Electrical Code (NEC) requires that the grounding system create "a permanent, low-impedance circuit capable of safely carrying the maximum ground-fault current likely to be imposed on it...." The operative words here are “permanent”, “low-impedance”, and “capable.”  What TJ is suggesting does not meet this definition.

“permanent”: Code compliant bonding of the Neutral of a portable generator to its' frame is not as simple as putting an external jumper between the ground and neutral of an open receptacle as TJ suggests here. A twist-lock plug end that can be mistakenly removed or not fully engaged if not twisted does not meet the definition of permanent.  I have had electrical inspectors kick my ground clamps to make sure that they are permanent.

 “low-impedance”: The prescribed impedance of Earth Ground according to the NEC is 25 Ohms.  It usually takes a 10’ rod, and sometimes two, to get 25 Ohms to ground. It is highly unlikely that TJ’s 2’ rod will provide a code compliant ground.

“capable”: Jumping between the ground and neutral of an open receptacle as TJ suggests here will not likely meet the Code requirement of  "capable of safely carrying the maximum ground-fault current likely to be imposed on it” because  it is not a ‘listed” piece of equipment for that purpose.

(http://www.screenlightandgrip.com/images/generators/SB_GF_Neutral_Bond.jpg)

In open frame models, like the ES6500, you can simply add a Neutral Bond jumper from one of the generator winding leads to the frame (as pictured above.) In an EU series inverter generator, bonding the Neutral to Ground requires removing the main panel and inverter module to get behind the breakers, switches, sockets etc. - not easily done or undone. According to the Honda Service Bulletins, it should only be done by a qualified Honda service technician.

(http://www.screenlightandgrip.com/images/generators/SB_2Fault240V_Exposure.jpg)

The Neutral/Ground bond in a generator is not something to be taken lightly because in a double fault situation like that illustrated above, the two faults create a 240V exposure plus a current path resulting in Electrocution. For this reason it is critical that GFCIs be used effectively and that they operate reliably.  What TJ proposes below is not the most effective use of GFCIs under the circumstances. Mike has partially addressed why in his post above.

For the record, a 7.5kVA transformer which is sufficient for a 60A circuit does not weigh 200lbs.

Guy Holt, Gaffer
ScreenLight & Grip
www.screenlightandgrip.com
Guy,

You can take up your angst with Honda, not me.  They have created a UL-listed product that lives in the gray area between the NEC, OSHA, and UL rules.  I wish it was internally bonded with GFCIs onboard, but it isn't.
 
It's all well and good to climb on a high horse and toot a "safety at all costs" horn, but that isn't reality in many situations.  Have you ever tried to pull even a 2' ground rod out of the ground much less a 4' or 8' ground rod?  Are you proposing that people take apart rented generators to install a bond?  I would rather give people a $10 removable solution that is effective than have people give up and use the generator stock, and a 2' ground rod that might actually be used rather than an 8' ground rod that requires renting a back hoe to remove.  When and if your transformers become standard issue at equipment rental houses we can talk about whether that is theoretically better or not (I still believe it isn't, all things considered).  Until then, I would rather have a practical solution that solves the practical issues than a theoretical one that is unavailable. 

If the inspector doesn't like the "temporary bond", you are free to "temporarily unbond" it.
Title: Re: Generator question
Post by: Guy Holt on September 23, 2015, 03:11:43 PM
I would rather give people a $10 removable solution that is effective ... and a 2' ground rod that might actually be used rather than an 8' ground rod that requires renting a back hoe to remove.

A "solution" that won't pass inspection is not a solution.  Here is a tip for removing 8' ground rounds.  Grab the top with a pair of channel locks and twist back and forth. You will now be able to pull even an 8' rod out with ease - no back hoe required.

Guy Holt, Gaffer
ScreenLight & Grip
www.screenlightandgrip.com
Title: Re: Generator question
Post by: Jonathan Johnson on September 23, 2015, 03:21:48 PM
Here is a tip for removing 8' ground rounds.  Grab the top with a pair of channel locks and twist back and forth. You will now be able to pull even an 8' rod out with ease - no back hoe required.

That's not so easy in rocky soil. When driving rods in rocky soil, they tend to bend, and bent rods don't twist very well -- or pull out easily.

Whatever happened to Mike's "bed of nails" idea?
Title: Re: Generator question
Post by: Mike Sokol on September 23, 2015, 03:22:51 PM
If the inspector doesn't like the "temporary bond", you are free to "temporarily unbond" it.
I'm in western Maryland and have done hundreds of shows in this part of the country, and I've NEVER had an inspector give me any problems or make me shut down a show. And I've done sound for the last 3 inaugurations, Oprah Winfrey, Hilary Clinton, and even Desmond Tutu and Mother Theresa.

One of the sound companies I work for is doing sound for the Pope today in Washington DC, and I'll ask them when they get back if there was any inspector checking out their power distro, but I'm guessing no. I'm sure it's different in the movie industry with lots of deep pockets, but out in the rest of the country we never even SEE an inspector for most of these small festivals that run off of a portable generator or two. It's up to us to follow code and protect the musicians and ourselves. Just remember that there's a LOT of incorrect wiring out there, so test everything you plug into, and check for hot-chassis conditions as often as you can. And NEVER accept feeling a shock as normal or expected.   
Title: Re: Generator question
Post by: Mike Sokol on September 23, 2015, 03:26:02 PM
Whatever happened to Mike's "bed of nails" idea?
I've got all the parts and done a few fall of potential test runs with a standard 8' ground rod, but I haven't  built and tried it yet. Guess I better get cracking on it.
Title: Re: Generator question
Post by: TJ (Tom) Cornish on September 23, 2015, 03:31:27 PM
A "solution" that won't pass inspection is not a solution.  Here is a tip for removing 8' ground rounds.  Grab the top with a pair of channel locks and twist back and forth. You will now be able to pull even an 8' rod out with ease - no back hoe required.

Guy Holt, Gaffer
ScreenLight & Grip
www.screenlightandgrip.com
In my metro area, <10KW generators are exempt from inspection anyway, and in my experience an educated inspector (admittedly not all are, in which case you can remove the plug if directed while they're onsite and replace it afterward) would prefer an easily testable bond than nothing.

RE ground rods: Per NEC 250.34 they're not required for portable generators connected by cord and plug methods, which includes all of the EU series.

RE pulling out an 8' ground rod by twisting channel locks: You must have very different soil than we have.
Title: Re: Generator question
Post by: Guy Holt on September 23, 2015, 03:49:04 PM
That's not so easy in rocky soil. When driving rods in rocky soil, they tend to bend, and bent rods don't twist very well -- or pull out easily.

I have worked in New England, the land of rocky soil, all my professional life and I have never been unable to pull a 8' ground rod - bent or not.  Regardless, if you can't get it out, simply drive it the rest of the way in and leave it - they are cheap enough.  More than once I have gone to drive a rod in the earth around a tree in the tree strip of a city street only to find a rod left there by some crew that shot there before me.

Guy Holt, Gaffer
ScreenLight & Grip
www.screenlightandgrip.com
Title: Re: Generator question
Post by: Guy Holt on September 23, 2015, 04:04:32 PM
In my metro area, <10KW generators are exempt from inspection anyway.

Unfortunately that is not the case in the cities of Boston and Cambridge and other municipalities I am sure. Here they also have to be permitted by the Fire Marshall.

RE ground rods: Per NEC 250.34 they're not required for portable generators connected by cord and plug methods, which includes all of the EU series.

Lets remember that the NEC is a minimum standard.  Many municipal codes supersede the national code. Regardless, I believe we are all in agreement that an earth ground, in addition to a bond between the EGC and the Neutral, is required for reliable operation of GFCIs.

Guy Holt, Gaffer
ScreenLight & Grip
www.screenlightandgrip.com


Title: Re: Generator question
Post by: TJ (Tom) Cornish on September 23, 2015, 04:43:19 PM
Unfortunately that is not the case in the cities of Boston and Cambridge and other municipalities I am sure. Here they also have to be permitted by the Fire Marshall.

Lets remember that the NEC is a minimum standard.  Many municipal codes supersede the national code. Regardless, I believe we are all in agreement that an earth ground, in addition to a bond between the EGC and the Neutral, is required for reliable operation of GFCIs.

Guy Holt, Gaffer
ScreenLight & Grip
www.screenlightandgrip.com

Guy,

Over a beer I think you and I would agree on far more things than we would disagree.  Where we differ is the intersection of the various sometimes conflicting codes that may or may not be not in force in a particular situation.  I respect that in your municipalities and in the situations you work in, your product/method (I'm still not clear if you are selling something or if this is just part of your company's rental offerings) is a great solution.  What I hope you will concede based on significant experience between several posters is that the typical situation many of us run into in the course of this industry - particularly at the small event level where this thread originated - is somewhat different than what you're used to.  I agree in principle with your thoughts on the negative effects of harmonics, the superiority of an inverter generator to a conventional generator, the criticality of a neutral -> ground bond, the importance of GFCIs, and I'm sure many other things.

While it would be great for every poster to own their own EU7000 that is internally bonded and/or a transformer like you describe that may assist with some other factors (with some disadvantages, too) complete with 10' ground rods, that's not the reality for many of us in these particular trenches, nor is it required by code or practical efficacy.  Asking users to do too much may have the opposite effect of what you desire, in that users may end up being deterred based on perceived complexity or effort, whereas practical solutions are more likely to be implemented, even if they don't meet certain letters of the code in some circumstances. Where the rules are different, I expect the players know them and adapt accordingly.

If you see material safety issues with a presented option, then let's talk about it, but let's not get too lost in the bureaucracy, since it's not universally applied.
Title: Re: Generator question
Post by: Stephen Swaffer on September 23, 2015, 08:51:20 PM
A couple of tips for safely installing removing ground rods.  If you have water handy, push rod in and make small hole, pour in some water and work it add some and repeat in all likelihood with a little patience you can push even an 8' rod in sometimes clay will make it hard, but I have done over 20 that way in the last couple of months.  Easy to know if you hit something you don,t want to go through.

Leave a few inches sticking out if you want to remove it.  Wrap a short (2 foot) piece of log chain around it and a 6' pry bar (piece of 3/4" pipe) and use leverage to your advantage.

Grounding conductors are sized b y breakers. 20. Amp Ned a #12 up 60 can get by with a #10.

Ground bonds are safety related.  An OSHA principle I like is that it should take a tool to undo.
Title: Re: Generator question
Post by: Jamin Lynch on September 23, 2015, 09:05:55 PM
Where I live the ground is like frickin concrete....really. Driving a rod in the ground isn't easy.

What if I'm actually on a concrete or asphalt drive and they don't want a rod driven through? I was on an asphalt drive last Saturday and they wouldn't let the tent folks drive their stakes in.
Title: Re: Generator question
Post by: Rob Spence on September 23, 2015, 09:57:45 PM
This doesn't meet the letter but I believe the spirit...

I have a ground post on my distro that I use to bond the stage to ground. I have a #6 thhn green wire (actually several) with lugs on the ends. I use a pair of vice grips (not to be confused with dolly grips 😀) to fasten a cable to the metal of the stage.


Sent from my iPad using Tapatalk HD
Title: Re: Generator question
Post by: David Buckley on September 23, 2015, 10:21:19 PM
Given the presence of the GFCIs, the ground rods almost certainly serve no effective purpose whatsoever.  The generator sitting on soil, grass or concrete will have a low enough impedance to soil to provide a path sufficient to trip a GFCI should a fault to soil occur.  Its a bit of a misnomer, but the ground loop impedance required to trip a GFCI is somewhere around 10K ohms.

The NEC is a bit of an ass about installation ground rods anyway, which serve a somewhat different purpose in an installation, but that is a digression.  One can have one ground rod, if the measured impedance is less than 25 ohms.  Or two ground rods, with no requirement to meet any impedance objective.  Thus to achieve code compliance the easiest way is to just drive two ground rods, job done.

Title: Re: Generator question
Post by: TJ (Tom) Cornish on September 23, 2015, 10:25:01 PM
Given the presence of the GFCIs, the ground rods almost certainly serve no effective purpose whatsoever.  The generator sitting on soil, grass or concrete will have a low enough impedance to soil to provide a path sufficient to trip a GFCI should a fault to soil occur.  Its a bit of a misnomer, but the ground loop impedance required to trip a GFCI is somewhere around 10K ohms.

The NEC is a bit of an ass about installation ground rods anyway, which serve a somewhat different purpose in an installation, but that is a digression.  One can have one ground rod, if the measured impedance is less than 25 ohms.  Or two ground rods, with no requirement to meet any impedance objective.  Thus to achieve code compliance the easiest way is to just drive two ground rods, job done.
Agreed that GFCIs and ground -> neutral bonding are the big deal.  As mentioned above, NEC 250.34 exempts "cord and plug" generators anyway, so unless Jamin's jurisdiction has a special requirement, a ground rod falls into the "nice to have" category (assuming a bonded generator with GFCIs).
Title: Re: Generator question
Post by: Stephen Swaffer on September 23, 2015, 11:40:49 PM
Where I live the ground is like frickin concrete....really. Driving a rod in the ground isn't easy.

What if I'm actually on a concrete or asphalt drive and they don't want a rod driven through? I was on an asphalt drive last Saturday and they wouldn't let the tent folks drive their stakes in.

Grab a teenage guy eager to prove his manhood and let him have at it!

If they don't want a rod driven through, have them sign a release taking responsibility for any bad things that happen as a result-not likely much of a defense-but it might make them think a bit if their name is on the dotted line.

Actually 250.34 exempts generators using "cord and plug connected equipment".  Some inspectors and industry people would argue that distribution wiring (temporary or permanent) doesn't meet the definition of equipment found in Article 100.  A discussion beyond the scope of this thread for sure.

As for bonding Honda generators, let me throw out this thought.  Maybe Mike will want to split this off.

If I am using a typical genny to provide backup for my house with a 4 wire connection, the G-N bond is in my home panel.  If I use the same genny with a distro, G-N bond can be in the distro preferably with an external lug for bonding ground rods. stages, etc.

With a one circuit genny, why not use a similar scheme.  A 120 V 20 cordset to a box with a G-N bond and a GFCI installed which supplies all connected equipment?  Then, if something disconnects the G-N bond, power is disconnected as well.

Same could be done with a 2 circuit genny.  Both 120 V circuits can be run with 3 wires each to one box.  Internal to the box, both neutrals and grounds are connected in one common bond.  Then, no matter the combination-circuit A only, B only or A and B you have one and only one G-N bond-and again if that bond is lost so is power.  This should provide all of the safety of the transformer style bond with a lighter and less expensive setup.  It is failsafe and simple to use and requires no genny modifications.  If made commercially, I am sure an engineer could design a plug that would block the second outlet of a duplex on the genny-this being the main weak link in this scheme.

Thoughts?
Title: Re: Generator question
Post by: Mike Sokol on September 23, 2015, 11:44:41 PM
Given the presence of the GFCIs, the ground rods almost certainly serve no effective purpose whatsoever.  The generator sitting on soil, grass or concrete will have a low enough impedance to soil to provide a path sufficient to trip a GFCI should a fault to soil occur.  Its a bit of a misnomer, but the ground loop impedance required to trip a GFCI is somewhere around 10K ohms.

Remember that another important function of ground rods is to provide an earth-ground path for a nearby lightning strike. That's also why the wire connecting to the ground rod (the Grounding Electrode Conductor or GEC) shouldn't have any sharp bends, and soldering isn't allowed. Lighting has such a high rise-time and peak current, that a sharp bend offers enough impedance that lighting can jump off of the wire, and solder would of course melt and act like a fuse.
Title: Re: Generator question
Post by: Jonathan Johnson on September 24, 2015, 01:41:24 AM
I use a pair of vice grips...

Vise Grip is a brand of locking plier.

Vice grip probably has something to do with a prostitute's technique.
Title: Re: Generator question
Post by: David Buckley on September 24, 2015, 06:46:53 AM
Remember that another important function of ground rods is to provide an earth-ground path for a nearby lightning strike. ..........
Not going to disagree a word of your post.

But, in context, its not relevant, and doesn't provide a reason to have an earth rod.

A tiddly Honda generator is just a couple of foot tall, and as such would be really unlucky to be the subject of a direct strike.  The stage setup which the generator is powering is a far more attractive target, and may well get struck.  However, the generator is not necessarily bonded to the metalwork of the stage (unless you get the vice grips and a green wire!) or have an unintentional connection, DI box on steeldeck, or parcan bolted to scaff pole.  If the stage does get struck, then the stage is likely in direct contact with the soil or concrete and that will be the path that most current will take.  The cable between the generator and stage will, as you note, act as a choke, and thus there will be little current getting to the genset, and thus any ground rod would be moot anyway.  A direct strike will inflict considerable damage on everything on the stage and connected to it and nearby it.  This protection is really about induced currents from nearby strikes which is far more common, and again, because of the fast risetimes, the same considerations apply.

So, again, in this type of operation, with ground/neutral bonded, and GFCIs, a ground rod doesn't add any safety to the setup.  In entertainment electrics, where there are electrical risks, GFCIs are simply the best thing since sliced bread, and correctly used, will save lives.  If your show gets whacked by lightning, then all bets are off.  Its best not to have anyone anywhere near the stage or anything connected to it if the lightning breezes through.
Title: Re: Generator question
Post by: Steve M Smith on September 24, 2015, 07:25:40 AM
Vise Grip is a brand of locking plier.

Vice grip probably has something to do with a prostitute's technique.
It's more to do with correct English spelling vs. your Webster corrupted version!


Steve.
Title: Re: Generator question
Post by: Mike Sokol on September 24, 2015, 07:49:06 AM
Not going to disagree a word of your post.

But, in context, its not relevant, and doesn't provide a reason to have an earth rod....


While I'm talking about ground rods in general for permanent structures, I do believe they provide additional equipment protection from lightning for outside shows. Now I'm not talking about a direct lightning hit as you imply. There's virtually NO WAY to protect gear from that amount of voltage and current. I'm referring to nearby ground strikes which branch out over the surface of the earth for many hundreds of yards. And of course this isn't just a single generator poking up above the earth. It's many hundreds of feet of XLR and AC cable snaked around the ground to the FOH mixer, speakers which are often flown 20 feet or more above the earth, and the stage itself. Without solid earth grounding this becomes a great antenna for capturing and distributing lightning into something called a "side flash" where the lightning exits multiple pieces of gear and enters the earth, destroying all sorts of things.

Now, we could start an entire thread on lightning safety for humans in the area and probably should. But in this particular case I'm talking about saving the gear AFTER you've evacuated the stage crew, musicians and crowd. 

Also, while GFCIs are great for protecting humans using backline and frontline gear, I'm not sure they're the best idea for protecting your amp racks. In that case, there's typically some sort of twist-lock plug feeding a rack of gear with internal distribution to multiple amps. As I've noted before, everything leaks a little current to chassis ground, so a rack of ampllfiers fed by a single GFCI with a 5mA trip point will probably nuisance trip too often to be useful. And separate GFCI circuits for every amp in a rack won't fly. However, I do think that industrial level of GFCI trip points (30 mA) for an amp rack would likely be useful, but probably not to code. Yikes!!!

So the real question is how important it is to drive a ground rod for a portable generator on a small stage? And since everything's not going to be GFCI protected, and there's power distribution to multiple locations (Stage, Monitor World, FOH Console, etc...) then I believe a ground rod should be standard procedure for portable generators used for festival power. In recap, I believe neutral bonding and earth grounding your portable generator, then using GFCI outlets for stage power, and making sure the metal stage is bonded to the generator ground should be standard procedure.

Yeah, ground rods are a real PITA to remove, so let's get working on an alternative to the standard 8 ft rod driven in with a min-sledge hammer. I'll show you my plans next week for discussion by the swarm.
Title: Re: Generator question
Post by: Jamin Lynch on September 24, 2015, 09:34:08 AM
Would the same things apply to let's say a 25K Whisper Watt?

All the ones I've seen were just dropped off by the rental company, started up and plug and play. I've asked about ground rods and such but only get a dumb look just before they drive off.
Title: Re: Generator question
Post by: Stephen Swaffer on September 24, 2015, 10:08:19 AM

 However, the generator is not necessarily bonded to the metalwork of the stage (unless you get the vice grips and a green wire!) or have an unintentional connection, DI box on steeldeck, or parcan bolted to scaff pole.



These types of unintentional "bonds" are very dangerous-they can create a hazard yet not be a good enough connection to clear a fault-far better to have a solid bond and a ground connection.  Really can't leave safety to happenstance.


Another thing to keep in mind is that there is nothing magical about "ground rods".  A metal light pole is fastened to a concrete pier that comes close to meeting the requirements of a concrete encased electrode.  If this is a venue that is frequently used, consider having them install a permanent grounding point..  A local venue I use has a FOH location set up in front of the bandstand with a buried snake and power in a fiberglass underground box-pop off the cover and you have access, put the cover on and it provides no hazard for other uses at the park. Do something similar but stick a ground rod in.

If there are stands that are attached to concrete piers-again you have a decent Ufer ground.  If there is a tent, use one of their tent stakes if you can.

IMO, safety is important enough that we should not give reasons (excuses??) that it can't be done or that it is inconvenient.  The reason venue's don't make provision is because we let them get away with it.  I understand that if you are the jerk that won't just do it then it can cost business-OTOH if you present a reasonable suggestion-maybe an idea no one has thought of you might get them to appreciate it. A fiberglass hand box and ground rod wouldn't run over $200-consider a couple trips to the chiropracter and that wouldn't be a bad investment if it is a repeat venue for you. 
Title: Re: Generator question
Post by: Mike Sokol on September 24, 2015, 12:52:16 PM
If there are stands that are attached to concrete piers-again you have a decent Ufer ground.  If there is a tent, use one of their tent stakes if you can.
I did a gig last month where we had to park the 25KW genny in the parking lot on the asphalt, so I wasn't going to mess up their parking lot with a ground stake. But there was a tent already pitched nearby on the lawn with big 3 ft stakes and I had a clamp big enough to attach the genny ground wire to a stake already in place. Best part was I didn't have to drive anything or take it out later since that was the tent company's job. Still, if I had the ground rod and a mini-sledge I would have installed it, even though that wasn't "supposed" to be my job. Oh well...

Now, no inspectors showed up, even though we had a head's up that one would likely stop by. And I did confirm the neutral-ground bond on the genny was about 1/4 ohm, and we were on a concrete pad without a metal stage so no bonding to the stage  was needed. And while I wasn't grounded with an 8-ft ground rod, everything measured correctly with a Ground Loop Impedance Tester (of course) except for one of the stage distro boxes supplied by the rental company. The contractor who brought the stage power was a little embarrassed to find a broken ground lug on the distro connector. But that made me feel like I was doing my job.

As part of my bed-o-nails testing, I'm going to compare the ground impedance of a 3 ft tent stake to an 8 ft ground rod and my bed-o-nails Sokol Ground. And I do know a few guys on the NEC code committee who are discussing RV grounding requirements, so I can actually discuss this with an NEC committee that can give us an official answer that could be written into the next code cycle. I don't want to propose anything unsafe or illegal, just come up with a methodology that we all can use.     
Title: Re: Generator question
Post by: Guy Holt on September 24, 2015, 04:55:42 PM
Guy,

Over a beer I think you and I would agree on far more things than we would disagree.…  What I hope you will concede based on significant experience between several posters is that the typical situation many of us run into in the course of this industry … is somewhat different than what you're used to.  While it would be great for every poster to own their own EU7000 that is internally bonded and/or a transformer like you describe that may assist with some other factors (with some disadvantages, too) complete with 10' ground rods, that's not the reality for many of us in these particular trenches, nor is it required by code or practical efficacy.  Asking users to do too much may have the opposite effect of what you desire, in that users may end up being deterred based on perceived complexity or effort, whereas practical solutions are more likely to be implemented, even if they don't meet certain letters of the code in some circumstances. Where the rules are different, I expect the players know them and adapt accordingly.

What I run into in my line of work is not as dissimilar to what you encounter as you may think.  We provide power generation to a number of outdoor theatre productions, music videos, as well as rock shows large and small (see the speaker stack in the rap video below.) Since many lighting effects are tied to music we are quite familiar with dynamic loads. 

(http://www.screenlightandgrip.com/images/generators/Boomtown_Scene_Comp.jpg)
2010 BET Hip Hop Awards “Director of the Year” Nahala Johnson, aka "Mr. Boomtown", directing his latest Rap Video: an outdoor dance party with DJ and dancers on top of a speaker stack (upper left.)

I am not suggesting the use of small portable transformers with portable generators because I sell them, but because as a working gaffer I find that they solve a number of issues related to the use of portable generators in production in general.

(http://www.screenlightandgrip.com/images/generators/Boomtown_SetUp_Comp_Web.jpg)
A modified Honda EU6500is supplies power to set (far left.) A 60A Full Power Transformer/Distro compensates for line-loss of 300’ cable run (left center) to assure 120V line level to 4K HMI (far right), Speaker Stack, Amplifiers, Set Monitors, Battery Chargers, & DIT station (Center.) 60A Bates Splitters, Extensions, and Gang boxes distribute power from Transformer around set (right center.)

I would hate to see someone be deterred from using them when they offer a solution because of a false perception obtained in this thread. For this reason I would like to address several false assumptions and misleading statements that have been posted.

Running all of your loads on a single 120 V circuit doubles your voltage drop compared to running the same load on a 240 volt circuit.

This argument doesn’t really apply to the use of step-down transformers because  transformers are 240V loads, and since in this application they would be used next to the amp rack, far from the generator as possible, there is no more line-loss than if the amps were powered at 240V.

Of course, a 120/240 volt circuit requires an extra wire.  So your pro's/con's would be to compare cost of 3 wire vs 4 wire vs cost of transformer.

Because transformers return no current, the neutral conductor can be dropped. Which means that you can use 10/3 SO cable which is lighter and cheaper than the 10/4 SO cable you would use with a L14-30 120/240 distro.

Yes you can add a transformer at the end of the run-but that adds complexity to distribution plus potential issues with getting a ground rod vs with a genny typically parked outside away from production.

A step-down transformer actually simplifies distro.  You can use off-the-shelf and straightforward 120V distro panels rather than more complicated custom panels that combine 120V and 240V receptacles. And as previously noted you don’t have to worry about balancing your loads on the two legs of a generator because a 240V-to-120V transformer splits whatever load is placed upon it (which is why there is no return current.)

As for the floating neutral-it is my understanding that can be fixed with an appropriate bonding jumper.  I simple low cost solution.

The simple  low cost solution may not pass inspection (see above for details.)

If the generator has voltage drop under load, transformer taps would work well for a steady load - under a dynamic load such as audio, the voltage would rise, perhaps to unacceptable levels when the generator was lightly loaded- making transformer taps a less than ideal solution.  The longer (higher impedance) your run, the greater your variation as the load varies.

Actually the opposite is true.  The magnetizing current of a step-down transformer puts a “phantom” load on a generator that buffers dynamic loads like power amps without adding to the overall loading of the generator. The net effect is that the generator sees a more consistent load with less wide disparities. As a result, there is less fluctuation of voltage when dynamic loads are powered through a step-down transformer than when they are powered directly off a generator.  Why this is the case is more complicated than I have time to get into here – I will try to put together a more detailed explanation in the near future.

If you see material safety issues with a presented option, then let's talk about it, ….

I do see safety issues with the statements below,  but it is more complicated than I have time to get into here – I will try to put together a detailed response in the near future.

... again, in this type of operation, with ground/neutral bonded, and GFCIs, a ground rod doesn't add any safety to the setup.....

... Get two inline GFCI devices like these: http://www.amazon.com/TRC-26020008-6-Shockshield-Protected-3-Outlets/dp/B000HHQIK2 and plug them into the two NEMA 5-20 receptacles on the generator....

Guy Holt, Gaffer
ScreenLight & Grip
www.screenlightandgrip.com
Title: Re: Generator question
Post by: Mike Sokol on September 24, 2015, 10:05:56 PM
This thread has run its course so I'm locking it. We'll continue discussion of the various topics later.

Mike Sokol