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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: Justin Schack on August 27, 2014, 10:40:28 AM

Title: AC Power for small outdoor event
Post by: Justin Schack on August 27, 2014, 10:40:28 AM
I am new to these boards and far from a pro sound engineer so my apologies in advance for the basic nature of my question, or if this topic has been covered in previous threads.

I could use some advice on AC power for a very small setup for an outdoor block party. Four-piece band - two electric guitars, one electric bass and a drum kit. Two JBL 515's for mains and two small Behringer powered floor monitors. Mackie mixer with 6 mic inputs and 2 stereo channels. Hoping to use the PA just for 2 or 3 vocal mics (but may also run an acoustic guitar into the Hi-Z input for some songs instead of a second electric guitar) but would consider miking guitar amps or running bass direct if needed. There probably won't be more than 100-200 people in the "audience" and I'm told we'll be setting up on the street, with heavy-duty extension cords from someone's house providing our AC power.

My main question is - should the extension-cord method be OK for that rig? I have 2 Furman 6-receptacle floor power conditioners and am thinking one of those will plug into the female end of the extension cord running from someone's home. I'll need more than 6 outlets - a total of 10 by my count (one mixer, four powered speakers, three instrument amps and two pedalboards) so either will need to daisy chain one Furman into the other or run 2 extension cords from the house. When I played in bands in high school and college - many years ago - setups like that mostly worked OK but I do remember some occasions in which noise and mikes that would deliver a little shock if you ate them caused problems. I'm slowly dipping my toes back into playing live with other musicians after many years and have not used this equipment outdoors yet.

I'm not looking for pro-quality sound here. Just want to make sure the setup is safe and sounds "good enough" for a few old dudes playing classic and alternative-rock covers in a casual setting.

Again, apologies for the basic nature of the inquiry but I figure this should be an easy one for the members here. Thanks in advance for any thoughts or advice.
Title: Re: AC Power for small outdoor event
Post by: Scott Holtzman on August 27, 2014, 10:43:59 AM
I am new to these boards and far from a pro sound engineer so my apologies in advance for the basic nature of my question, or if this topic has been covered in previous threads.

I could use some advice on AC power for a very small setup for an outdoor block party. Four-piece band - two electric guitars, one electric bass and a drum kit. Two JBL 515's for mains and two small Behringer powered floor monitors. Mackie mixer with 6 mic inputs and 2 stereo channels. Hoping to use the PA just for 2 or 3 vocal mics (but may also run an acoustic guitar into the Hi-Z input for some songs instead of a second electric guitar) but would consider miking guitar amps or running bass direct if needed. There probably won't be more than 100-200 people in the "audience" and I'm told we'll be setting up on the street, with heavy-duty extension cords from someone's house providing our AC power.

My main question is - should the extension-cord method be OK for that rig? I have 2 Furman 6-receptacle floor power conditioners and am thinking one of those will plug into the female end of the extension cord running from someone's home. I'll need more than 6 outlets - a total of 10 by my count (one mixer, four powered speakers, three instrument amps and two pedalboards) so either will need to daisy chain one Furman into the other or run 2 extension cords from the house. When I played in bands in high school and college - many years ago - setups like that mostly worked OK but I do remember some occasions in which noise and mikes that would deliver a little shock if you ate them caused problems. I'm slowly dipping my toes back into playing live with other musicians after many years and have not used this equipment outdoors yet.

I'm not looking for pro-quality sound here. Just want to make sure the setup is safe and sounds "good enough" for a few old dudes playing classic and alternative-rock covers in a casual setting.

Again, apologies for the basic nature of the inquiry but I figure this should be an easy one for the members here. Thanks in advance for any thoughts or advice.

The shock was due to improper grounding and can kill.  You need to check out our power and grounding section.

It's all distance.  How far are you going to run.

Add up all the current draws of the devices also.

I would certainly use 220/240V and slit it  back down to 120 at the stage with a small distribution box.

Title: Re: AC Power for small outdoor event
Post by: Mike Sokol on August 27, 2014, 11:02:43 AM
Nate,

Please change your visible name to your actual name and we'll be able to help you. This board requires that everyone use their real name before posting.

Welcome aboard.

Mike Sokol

I am new to these boards and far from a pro sound engineer so my apologies in advance for the basic nature of my question, or if this topic has been covered in previous threads.

Title: Re: AC Power for small outdoor event
Post by: g'bye, Dick Rees on August 27, 2014, 11:03:34 AM
No to "extension cords".

They're likely to be too light a gauge and not rated for your use.  Some home-owner power tools, perhaps, but not for use where people are on the user end and subject to harm should a fault occur.  In addition, you cannot start connecting these things together to get longer runs without twist-lock connectors in approved waterproof shields.


You'd be better off with a small generator, but that opens up more questions...and don't forget that someone has to be carrying liability insurance for this.
Title: Re: AC Power for small outdoor event
Post by: Justin Schack on August 27, 2014, 11:15:43 AM
Nate,

Please change your visible name to your actual name and we'll be able to help you. This board requires that everyone use their real name before posting.

Welcome aboard.

Mike Sokol

sorry about that - just did. thanks.
Title: Re: AC Power for small outdoor event
Post by: Ray Aberle on August 27, 2014, 11:38:42 AM
So if you wanted to pull house power, I would get a range plug to CS6364 adapter, 100' of CS twist lock cable, and a spider box. Plug it into the house's stove/range plug, which will get you 50A at 220v. The spider box will then break everything back down to 20A circuits for you, and this will be more then plenty amounts of power.

The well-meaning homeowner who wants to bring you "heavy duty extension cords," -- well, as Dick mentioned, they probably won't be the right type, and could therefore be dangerous.

If you wanted to go the small generator route, a Honda EU3000is would work great, and be plenty of power for your rig as well.

My main question is - should the extension-cord method be OK for that rig? I have 2 Furman 6-receptacle floor power conditioners and am thinking one of those will plug into the female end of the extension cord running from someone's home. I'll need more than 6 outlets - a total of 10 by my count (one mixer, four powered speakers, three instrument amps and two pedalboards) so either will need to daisy chain one Furman into the other or run 2 extension cords from the house.
It's not the number of outlets you need that you should be calculating... as Scott alluded to, you need to factor in the actual power draw for everything. You may be OK on one 20A circuit, or you may require two. Or three.

-Ray
Title: Re: AC Power for small outdoor event
Post by: Mike Sokol on August 27, 2014, 12:30:04 PM
The well-meaning homeowner who wants to bring you "heavy duty extension cords," -- well, as Dick mentioned, they probably won't be the right type, and could therefore be dangerous.

The two BIG issues with extension cords are voltage drop and failed EGC (Equipment Grounding Conductor) what's commonly referred to as the "safety ground".

Voltage Drop: One thing that a lot of technicians fail to consider is that the suggested minimum gauge for a particular amperage draw is calculated on a 100 ft total run. So those orange "big box" extension cords will certainly be too small and produce too much voltage drop under load. This low voltage can make amplifier and mixers shut down, not to mention any guitar players amplifier with on-board emulation. Basically, everything is a computer nowadays.

Safety Ground: If you received a shock from a microphone on a previous gig, then something on your stage had a failed EGC connection (safety ground). Could have been at the power cord feeding the mixer (which would electrify all the microphones) or a single guitar amp (which would electrify the guitar strings) and possibly the entire extension cord from the "garage power". I find that outside receptacles on houses or in garages live a hard life, and many times were never wired correctly from the start. With an open ground your PA systems "ground plane" can easily float up to 60 volts AC. And if you're unlucky enough to be plugged into an older home that was "upgraded" to grounded outlets improperly using a Bootleg Ground, then there's always the possibility of something I call an RPBG (Reverse Polarity Bootleg Ground). See http://ecmweb.com/contractor/failures-outlet-testing-exposed (http://ecmweb.com/contractor/failures-outlet-testing-exposed) for an overview. In any event, this "hot-ground" condition can become deadly in a heartbeat, so NEVER use a PA system that's shocked you, especially outside near the wet grass.

I do concur with the Honda 3KW generator option. These are very quiet, sip gasoline, and make some of the cleanest AC power available. You may be able to find a local shop that can rent you one for the day. Check to see if they can rent you some heavy "power drops" while you're at it. You really should drive a ground rod to ground the genny, but that's not legal to do without consulting a "Miss Utility" service that shows you where the water and gas pipes are underground. So as much as I like to ground generators, I'm sure there have been thousands or even millions of small stages like your run safely without earth grounding the generator. However, note that you still need to use "grounded" power cords to hook everything up to your genny, since a guitar amp with a broken off ground pin on the power cord can still kill a musician.

Lastly, the main reason why that power distro cables for sound systems uses such heavy rubber insulation is that they know people will be stepping on the cords, cars will be running over them, and lawn chairs will be sitting on them. That can cause a break in the wire itself, or a break in the insulation and create a shock point.

And that's why we also carry liability insurance for these shows. You don't need it when everything goes right.... You need it for when something goes wrong. Consider the insurance needed to cover those firefighters who were shocked and nearly killed when their boom truck got too close to an overhead power line. I would not want to be writing out that check myself.
Title: Re: AC Power for small outdoor event
Post by: Ray Aberle on August 27, 2014, 01:21:50 PM
I was thinking about the voltage drop, but knowing that some of the big-box stores do sell 14ga and even 12ga pre-made cables, I was going under the presumption that the "heavy duty cables" referenced would be at least 12ga. :) I was thinking more of just the size and strength of the jackets...

Also re the shock on previous gigs, keep in mind the OP said that was years and years ago... so I am *hoping* that is not a problem still. :)

- Ray "now wondering if the OP's name is Nate or Justin" Aberle       

.haha
Title: Re: AC Power for small outdoor event
Post by: Justin Schack on August 27, 2014, 02:00:09 PM
Thanks so much for the quick responses, folks.

So, judging from the advice so far I have two options:

1. access 220v house power, do not rely on "extension cords" to transmit from that source but rather something like twist-lock cable and a spider box to convert back to 120v power that can be accessed by our various equipment on stage. I have to admit I have no idea what twist-lock cable and spider boxes are, so that has me leaning more toward option 2:

2. use a portable generator - honda 3KW EU3000is being a good option.

This is a block party run by a neighborhood association, so I can ask the organizer if they can fit a generator rental into the budget, as that seems the cleanest/easiest approach. Or perhaps someone in the neighborhood already owns such a unit.

In either case, I should be mindful of the total current draw of all devices being used on stage. One quick question regarding that: should I include every stomp box being used by guitarists, or just the requirements of the pedalboard power supplies (pedal power in both cases)? I'd think the latter, but as you can tell I'm not an electricity expert so figure it's worth checking.

Finally, I appreciate very much the liability insurance recommendation. But I'm not exactly clear on it. Are you suggesting the band (and/or me as the equipment supplier/operator) should have insurance against the risk of someone being injured if there's an electrical mishap? Or perhaps that's something I can persuade the neighborhood association to shoulder as well (or require them to sign some kind of release holding us/me harmless from such injuries and assuming the risk)?

Thanks again - this is a big help!

Oh, and my name is Justin - Nate is just an internet alias :)
Title: Re: AC Power for small outdoor event
Post by: Justin Schack on August 27, 2014, 02:03:33 PM
And, yes, the issues with shocks were from many years ago. Not something I've experienced at all with my current rig. Using tube amps in good condition and recently purchased mixer/powered speakers.
Title: Re: AC Power for small outdoor event
Post by: g'bye, Dick Rees on August 27, 2014, 02:23:50 PM
If you're setting up any kind of gear at all in an area where other people will be using it and/or passing around, over or under it, you should be insured for liability.  Even if the event sponsor has a liability policy and signs you off on a hold-harmless rider, you don't want to go to court with that.

Title: Re: AC Power for small outdoor event
Post by: Scott Holtzman on August 27, 2014, 03:46:20 PM
And, yes, the issues with shocks were from many years ago. Not something I've experienced at all with my current rig. Using tube amps in good condition and recently purchased mixer/powered speakers.

Using the dryer plug is not acceptable.  Dryer plug is three wires two phases and a neutral.  Without a safety ground.

Now you can take the ground out and connect it to a regular outlet but this is not to the NEC because the safety ground can be disconnected without disconnecting the mains.

Code requires all sub panels (this application is a sub panel) to have four wires of the appropriate size, period, end of conversation. 

Do people make other temporary accommodations every day?  Of course they do.  Is it safe, no?  Is it right, no.  Does it void your liability coverage, for sure.

Title: Re: AC Power for small outdoor event
Post by: Ray Aberle on August 27, 2014, 04:07:03 PM
Using the dryer plug is not acceptable.  Dryer plug is three wires two phases and a neutral.  Without a safety ground.

Now you can take the ground out and connect it to a regular outlet but this is not to the NEC because the safety ground can be disconnected without disconnecting the mains.

Code requires all sub panels (this application is a sub panel) to have four wires of the appropriate size, period, end of conversation. 

Do people make other temporary accommodations every day?  Of course they do.  Is it safe, no?  Is it right, no.  Does it void your liability coverage, for sure.

... Scott, who said anything about using the dryer plug??  :o
Title: Re: AC Power for small outdoor event
Post by: g'bye, Dick Rees on August 27, 2014, 04:13:27 PM
... Scott, who said anything about using the dryer plug??  :o

Me!  Me!  I know!!

No one.

There was a range plug mentioned...
Title: Re: AC Power for small outdoor event
Post by: Stephen Swaffer on August 27, 2014, 04:23:27 PM
Both range and dryer plugs used to be 3 wire.  NEC requires (I think since 2005 or 2008) both to be 4 wire.  Age of house/local codes/inspection requirements will determine what is installed.

No doubt, eventually you will start to see 4-wire receptacles with bootleg grounds-just human nature!
Title: Re: AC Power for small outdoor event
Post by: g'bye, Dick Rees on August 27, 2014, 04:25:38 PM
Both range and dryer plugs used to be 3 wire.  NEC requires (I think since 2005 or 2008) both to be 4 wire.  Age of house/local codes/inspection requirements will determine what is installed.

No doubt, eventually you will start to see 4-wire receptacles with bootleg grounds-just human nature!

Thus the need for a Fluke meter and the knowledge of how to use it.

To the OP:

It's not really a simple question...
Title: Re: AC Power for small outdoor event
Post by: Ray Aberle on August 27, 2014, 04:32:43 PM
Me!  Me!  I know!!

No one.

There was a range plug mentioned...

$2 will get you who mentioned the range plug... :-P

But really, these are all of the joys that come with doing something correctly! As the saying goes, integrity is doing the right thing when no one is looking-- it doesn't matter if you'll get inspected or not, you should always endeavor to be as complete as possible.
Title: Re: AC Power for small outdoor event
Post by: Scott Holtzman on August 27, 2014, 05:27:00 PM
I get to say it again learn something new.  Never seen a four prong range in anything but commercial.  l
Title: Re: AC Power for small outdoor event
Post by: Mike Sokol on August 27, 2014, 05:50:12 PM
In either case, I should be mindful of the total current draw of all devices being used on stage. One quick question regarding that: should I include every stomp box being used by guitarists, or just the requirements of the pedalboard power supplies (pedal power in both cases)? I'd think the latter, but as you can tell I'm not an electricity expert so figure it's worth checking.

No need to count up the stomp box and pedalboard power supplies. Those things draw next to nothing. Heck, we used to run them all from 9-volt batteries. But you do need to determine the current draw of your power amps and monitors, as well as the musician's stage amps, especially bass amps and tube guitar amps.

However, this total calculation is not always simple since you have to take into account the crest factor and SPL of music you're expecting to do (no kidding). Let consider two different types of acts with vastly different power draw. First up is a rather quiet Celtic act with female singers, pipes and a violin. In that case your amplifiers will be coasting along and probably not drawing much over idle current, perhaps 1/10 of rated wattage with a crest factor of 10:1 (peak to average level) or higher. So even a 450-watt speaker might be drawing only 40 or 50 watt for this act. Now imagine you've got a Reggae or Hip-Hop act up next with LOTS of bass. In that case, your crest factor might approach 1:1. That means that your 450-watt speaker will likely be drawing full power for long periods of time. And since amplifiers are not 100% efficient, it's likely to be drawing more like 600 watts or so.

Now, those of us who do live sound for a living get a pretty good feel of what we can get away with for different acts and styles of music. So I would probably do the Celtic act from a single 20-amp service and not have any problems. But I would certainly want to pull out the big guns with a heavy 50-amp/240-volt (or even more amperage) distro when I'm doing a Reggae or Hip-Hop act.

Also realize that you might find that someone has installed a bunch of lights under the tent and expects to power everything from your generator or distro when the sun goes down. After all, they see all those big cables and assume you've got LOTS of extra power to spare. So make sure you're not responsible for lighting power as well.   

That being said, what kind of acts are expected and how loud will it be? And do I have to power any lights. That's how I always start to calculate power requirements for a gig.
Title: Re: AC Power for small outdoor event
Post by: Mike Sokol on August 27, 2014, 05:52:40 PM
I get to say it again learn something new.  Never seen a four prong range in anything but commercial.  l

Scott (and everyone else). Try not to fixate on the range/dryer plug question and lets try to help this guy. He's obviously trying to learn something about AC power, so lets teach...  ;D
Title: Re: AC Power for small outdoor event
Post by: Justin Schack on August 28, 2014, 09:18:14 AM
Thanks again for the advice, folks.

Regarding liability insurance, any recommendations on where to buy it cheaply and efficiently (perhaps online)? Or a ballpark estimate of how much it should cost? Can it be used just for a single event or is it applied over a period of time to cover multiple events/continued usage?

I continue to lean toward the generator route — we are in the Northeast US so with all the hurricanes we've seen in recent years there's a good chance someone in the neighborhood will have a portable one that suits. I'm also going to work on adding up all the current draws of our amps, mixer and speakers (thanks for the clarification about pedals, Mike). But I also have been reading on other forums that using very heavy-duty extension cords from a single wall outlet or outdoor GFCI outlet (or perhaps two outlets) can successfully run a small rig like mine. And a couple of weeks ago I ran the same equipment in a small Knights of Columbus hall using only the wall outlets on and near the stage, in combination with my two Furman 6-outlet conditioners. I don't know much at all about 20-amp circuits or whether all of those outlets were on the same circuit or not, but we had no noise issues with the equipment and no power interruption issues either. Additionally, none of the other forums I've researched are dedicated to AC power and grounding like this one is, and I know you all are experts there whereas the other forums (places like Gearslutz) are generalists. But I guess in light of the aforementioned factors I'm still wondering whether, if all our equipment uses "grounded" power cords and balanced connections for mics and speakers, the one-or-two-wall-outlets-fed-by-heavy-duty-extension-cords method will truly be unsafe.

Really appreciate everyone's time and attention to my newbie/novice problem. Thanks again.
Title: Re: AC Power for small outdoor event
Post by: Tim McCulloch on August 28, 2014, 09:57:56 AM
Using the dryer plug is not acceptable.  Dryer plug is three wires two phases and a neutral.  Without a safety ground.

Now you can take the ground out and connect it to a regular outlet but this is not to the NEC because the safety ground can be disconnected without disconnecting the mains.

Code requires all sub panels (this application is a sub panel) to have four wires of the appropriate size, period, end of conversation. 

Do people make other temporary accommodations every day?  Of course they do.  Is it safe, no?  Is it right, no.  Does it void your liability coverage, for sure.

Code requires that present day electric clothes dryers use 4 wire service, although 3 wire is "grandfathered" in IF it was installed x years ago.
Title: Re: AC Power for small outdoor event
Post by: Mike Sokol on August 28, 2014, 02:13:36 PM
But I guess in light of the aforementioned factors I'm still wondering whether, if all our equipment uses "grounded" power cords and balanced connections for mics and speakers, the one-or-two-wall-outlets-fed-by-heavy-duty-extension-cords method will truly be unsafe.


Did you already tell us how long of a run this would be from these "home" outlets to the stage? If not, please walk it off and let us know. I typically rent something called Yellow Jacket cable ramps for gigs where the power wires cross paths with pedestrians or cars. Maybe you have a local sound company that will donate some Yellow Jacket rentals for the good of the neighborhood. Or at least they can give you a cheap deal. They're typically 3 ft in length and heavy as all get out, but you can drive a truck over them while protecting any power cables.   

Secondly, any extension cord recommendations even from a distro or generator to the stage and speakers will need to include wire gauge, at the very least. Do you already have extension cords? If so, exactly what are they?

For liability, my home insurance agent was able to provide me with a rider for sound gear and liability coverage for my little gigs many years ago. This was a yearly policy and wrapped up into my homeowners liability policy. Essentially, you don't want to be the fall guy if some guy falls (or something like that). My current business liability policy isn't really cheap, but it covers me no matter what sort of gig I'm doing anywhere in the country (USA). But I need a rider if I go out of the country, even to Canada.   
Title: Re: AC Power for small outdoor event
Post by: Scott Holtzman on August 29, 2014, 03:31:30 AM
Did you already tell us how long of a run this would be from these "home" outlets to the stage? If not, please walk it off and let us know. I typically rent something called Yellow Jacket cable ramps for gigs where the power wires cross paths with pedestrians or cars. Maybe you have a local sound company that will donate some Yellow Jacket rentals for the good of the neighborhood. Or at least they can give you a cheap deal. They're typically 3 ft in length and heavy as all get out, but you can drive a truck over them while protecting any power cables.   

Secondly, any extension cord recommendations even from a distro or generator to the stage and speakers will need to include wire gauge, at the very least. Do you already have extension cords? If so, exactly what are they?

For liability, my home insurance agent was able to provide me with a rider for sound gear and liability coverage for my little gigs many years ago. This was a yearly policy and wrapped up into my homeowners liability policy. Essentially, you don't want to be the fall guy if some guy falls (or something like that). My current business liability policy isn't really cheap, but it covers me no matter what sort of gig I'm doing anywhere in the country (USA). But I need a rider if I go out of the country, even to Canada.

Good extensions cords are not cheap either.  If it's 300' you are going to spend $500.00  I presume we are talking well over 100' or we would not be having the discussion.  As stated please walk off the distance so we can give you the numbers and let you make an informed decision.

Also, if you are a homeowner the rider for the gear is a super suggestion.  Additionally if you are a good risk I also highly recommend an umbrella policy.  Personal liability.  I volunteer so much that it lets me sleep at night knowing that I am covered if I do something stupid etc.

Title: Re: AC Power for small outdoor event
Post by: Jonathan Johnson on August 29, 2014, 12:06:16 PM
This is a bit off topic from the general discussion of the thread, but I wanted to address something else I picked up on in your original post.

Mackie mixer with 6 mic inputs and 2 stereo channels. Hoping to use the PA just for 2 or 3 vocal mics (but may also run an acoustic guitar into the Hi-Z input for some songs instead of a second electric guitar) but would consider miking guitar amps or running bass direct if needed.

Unless you are plugging the acoustic guitar directly into the mixer with a cord no longer than the typical length of a "guitar cord" -- that is, if you are plugging into a snake that goes to the mixer some distance away -- you'll want to use a DI box. If it's a passive pickup, use an active DI box (or a Hi-Z to Low-Z microphone balun, BUT you might not get a hot enough signal at the mixer). If it's an active pickup (there's a battery in the guitar), you can use a passive or an active DI box. The other end of the DI box plugs into the XLR microphone input of the mixer channel.

You can connect a guitar amp's line or speaker output to the mic input of a mixer using a DI box. If using the speaker output, you'll need to use the DI boxes attenuation switch.

Trying to feed a mixer through a hundred feet of unbalanced cable without converting from Hi-Z unbalanced to Low-Z balanced can result in degradation of the sound quality.
Title: Re: AC Power for small outdoor event
Post by: Mike Sokol on August 29, 2014, 01:15:25 PM
Trying to feed a mixer through a hundred feet of unbalanced cable without converting from Hi-Z unbalanced to Low-Z balanced can result in degradation of the sound quality.

It also makes a great antenna for any AM radio stations in your area. And you can tune to different radio stations in your area by selecting different length mic cables. I'm NOT making this up.

But that's all OT and belongs on another forum here. However, I just can't resist a good Hi-Z story.
Title: Re: AC Power for small outdoor event
Post by: Justin Schack on August 29, 2014, 02:39:53 PM
Thanks for the advice about the homeowner's insurance rider and umbrella policy. I'm going to look into both of those.

Regarding the length of the run, I don't know exactly and don't live in the neighborhood (it's a friend's party) but I have asked them to estimate. This is in a fairly densely populated suburb, with lots that are generally no more than 1,500-1,750 sq ft, so my guess is the run will be somewhere around 100-200 feet.

I personally don't know what extension cords are contemplated here. My guess is they're the run-of-the-mill orange jobs a homeowner would use to power holiday lights. But I don't know, and don't intend on supplying them myself unless I absolutely have to. The point about buying high-quality extension cords at the length required (and cost of same) is well taken. I continue to think a generator is the best option but it also would be good to know if we could get away with just accessing one or more wall/outdoor GFCI outlets using extension cords.

Thanks for the advice about the Hi-Z input. The mixer would be close to the stage (unfortunately I'll be running it myself and relying on bandmates/friends to listen and provide input when soundchecking rather than having a dedicated desk location somewhere out in the audience area) so it won't be a long cable run from the acoustic guitar (it's a passive under-saddle Baggs pickup in a Gibson J-45).
Title: Re: AC Power for small outdoor event
Post by: Mike Sokol on August 29, 2014, 03:52:45 PM
I personally don't know what extension cords are contemplated here. My guess is they're the run-of-the-mill orange jobs a homeowner would use to power holiday lights.

And that's a recipe for disaster. You'll note there's a new thread on this forum about getting a serious shock and damaging gear from a bass amp with a broken power cord of some type. See http://forums.prosoundweb.com/index.php/topic,151222.0.html (http://forums.prosoundweb.com/index.php/topic,151222.0.html)

You'll be much happier and safer if you can get someone to supply a Honda inverter generator as mentioned above. And many RV owners have a pair of the Honda EU2000 generators linked together with a special cable that makes it into a very nice 4,000 watt genny. Ask your neighborhood contact to find out if anyone has an RV in the area. They'll be proud to loan you their Honda generator for the good of the neighborhood party, especially if it helps stop everyone from complaining about their big RV parked in the driveway.  ;D 
Title: Re: AC Power for small outdoor event
Post by: g'bye, Dick Rees on August 29, 2014, 04:00:08 PM
That's Honda EU Inverter series.  Don't try to get by with anything else.  A "generator" is not a Honda.  Even the non-inverter Hondas won't do.

100' is no good.  Besides dealing with proper cabling, you have a 100' tripping hazard.
Title: Re: AC Power for small outdoor event
Post by: Mike Sokol on August 29, 2014, 04:42:54 PM
100' is no good.  Besides dealing with proper cabling, you have a 100' tripping hazard.

I once did a festival gig down in Annapolis where we had to run a snake and power 60' across a parking lot from the stage to my FOH mix position. So we put down a bunch of Yellow Jacket cable ramps and set orange traffic cones every 10 ft or so. Now this was a black and yellow striped ramp with bright orange cones you probably could have seen from space. But even before the concert began and with nobody else in the parking lot, one lady walked right up to the cable ramps, tripped over a traffic cone, and fell flat on her face. She was walking and talking to her friend and never looked down. Ouch! :o
Title: Re: AC Power for small outdoor event
Post by: g'bye, Dick Rees on August 29, 2014, 04:54:02 PM
I once did a festival gig down in Annapolis where we had to run a snake and power 60' across a parking lot from the stage to my FOH mix position. So we put down a bunch of Yellow Jacket cable ramps and set orange traffic cones every 10 ft or so. Now this was a black and yellow striped ramp with bright orange cones you probably could have seen from space. But even before the concert began and with nobody else in the parking lot, one lady walked right up to the cable ramps, tripped over a traffic cone, and fell flat on her face. She was walking and talking to her friend and never looked down. Ouch! :o

Darwin.
Title: Re: AC Power for small outdoor event
Post by: Ray Aberle on August 29, 2014, 07:44:43 PM
It is interesting to observe how people can trip more readily over cable ramps then they will if you just laid the cable out on the pavement... it's like, "we're doing this for your safety" yet it ends up being more risky? Awkward.
Title: Re: AC Power for small outdoor event
Post by: Mike Sokol on August 29, 2014, 08:05:34 PM
It is interesting to observe how people can trip more readily over cable ramps then they will if you just laid the cable out on the pavement... it's like, "we're doing this for your safety" yet it ends up being more risky? Awkward.

No matter how hard you try to idiot proof something, they're always making better idiots.  ::)
Title: Re: AC Power for small outdoor event
Post by: Ray Aberle on August 29, 2014, 08:22:37 PM
No matter how hard you try to idiot proof something, they're always making better idiots.  ::)

Then the AHJ will be all like "that's nice about the cable ramps. Now put up a sign warning people about them. And make sure the sign won't fall over."

Same series of events, generator at CenturyLink Field in Seattle for the Seahawks games. Generator sitting on property until well after the game-- "Blue Thunder" drum group is playing-- and I'm there having to stop people from climbing ON the generator... sheesh. Do I climb on the bumper of your car?!?
Title: Re: AC Power for small outdoor event
Post by: Mike Sokol on August 29, 2014, 09:12:07 PM
and I'm there having to stop people from climbing ON the generator... sheesh. Do I climb on the bumper of your car?!?

Only the hot chicks are allowed to dance on my subwoofers in front of the stage, but I think that's a universal law or something...  ;D
Title: Re: AC Power for small outdoor event
Post by: Eric Simna on August 29, 2014, 11:49:32 PM
It is interesting to observe how people can trip more readily over cable ramps then they will if you just laid the cable out on the pavement... it's like, "we're doing this for your safety" yet it ends up being more risky? Awkward.

And senior citizens are the worst when it comes to cable ramps.  I had one little old lady yell at me and say it was "stupid" to use that "bump."  She changed her mind after I explained the bump was better than if she tripped over the cables under that "bump."  I sometimes think they'd be safest if they were camouflaged.
Title: Re: AC Power for small outdoor event
Post by: Stephen Swaffer on August 30, 2014, 12:22:07 AM
Then the AHJ will be all like "that's nice about the cable ramps. Now put up a sign warning people about them. And make sure the sign won't fall over."


All he warning signs do is tell the AHJ that you know that you have created a hazard-and the hazard is still there.  What are you going to to do to eliminate the hazard??  Actually had an OSHA instructor point out that issue in regards to "Wet Floor" signs.  It really is a losing game.

If you borrow extension cords-even for short runs to a genny make sure you double check the ground prongs.  It seems like they are engineered to have a life expectancy of about 1/10th the power prongs.  Unless the cords are like new and well cared for they will be missing.

I agree we should not fixate on 3 wire/4 wire and it seems like the OP has already ruled out a distro.  I think the important thing for general knowledge is to understand that a 3 wire 220 V circuit is never acceptable for a distro supply; whereas, a 4 wire should be acceptable.  Doesn't matter whether it is dryer/range, resi/commercial/genny.....
 
Title: Re: AC Power for small outdoor event
Post by: Mike Sokol on August 30, 2014, 07:13:59 AM
If you borrow extension cords-even for short runs to a genny make sure you double check the ground prongs.  It seems like they are engineered to have a life expectancy of about 1/10th the power prongs.  Unless the cords are like new and well cared for they will be missing.

For the OP: Yes, broken off ground prongs on the extension cords are a big No-No and something you can't allow on your stage, no matter what the power source. You may be able to workaround a lot of other things, but that's the most important takeaway from this thread.
Title: Re: AC Power for small outdoor event
Post by: Jonathan Johnson on August 30, 2014, 02:35:42 PM
If you borrow extension cords-even for short runs to a genny make sure you double check the ground prongs.  It seems like they are engineered to have a life expectancy of about 1/10th the power prongs.  Unless the cords are like new and well cared for they will be missing.

They ARE engineered to have a shorter life expectancy, though I suspect the engineers don't realize it. The ground prongs are constructed similar to a crimp-on terminal. There's a ring the gets crimped onto the wire, then a narrow bridge to the prong, which is made pretty much identical to the crimp ring. The pin breaks at the bridge, which is just barely inside the molding. (If more of the tubular portion of the ground pin was in the molding, it would be stronger.) The power prongs are much thicker and wider where they join their respective crimp rings.

My extension cords are well cared for, and the prongs STILL break off after a couple of years. I think it should be standard practice to just replace the male end of an extension cord with the most heavy-duty plug you can buy as soon as you purchase it. Probably should do the female end, too, since the contacts on the factory molded ends tend to be weak and get loose quickly.
Title: Re: AC Power for small outdoor event
Post by: Guy Holt on August 31, 2014, 10:58:05 AM
That's Honda EU Inverter series.  Don't try to get by with anything else.  A "generator" is not a Honda.  Even the non-inverter Hondas won't do.

While the insistence that electrical cords have their ground pins in tact is important, in the context of power generated by Honda EU series generators, it is rather pointless. That is because the Honda EU generators have Floating Neutrals (no bond between the Equipment Grounding Conductor (EGC) and Neutral) and so fault currents will not go to the EGC as they are meant to.  In this context, any discussion of ground pins and the EGC as a low impedance path back to the power source to activate over-current protection is creating a false sense of security.

For the same reason, the test buttons of GFCIs create a false sense of security when they are used on the EU series generators.  Absent a Neutral to EGC bond, GFCIs will not operate on the Honda EU series generators.  A GFCI will only operate reliably if one side of the generator winding is grounded to the generator frame and EGC because otherwise fault current has no path back to the winding to complete the circuit. Only when Neutral is bonded to the EGC, will current go to the EGC to complete the circuit when there is a current leak. In other words, a complete circuit is required to create an imbalance and cause the GFCI to trip.

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

In this context, GFCI test circuits are misleading when they are used on Floating Neutral generators because the test button draws power from the Hot through its’ Current Transformer (CT) and back through the CT again to the Neutral via a Current Limiting Resister. The discrepancy caused by the Current Limiting Resister in the test circuit (illustrated above) will initiate the GFCI to trip even though there is in fact no Ground Fault Circuit for Fault Current to go to if there were a Fault. The false positive generated by GFCI test circuits on ungrounded Floating Neutral generators does nothing to eliminate faulty equipment and only creates a false sense of security.

These issues related to ground fault protection with Floating Neutral generators like the Honda EU series are well documented by The Construction Safety Association of Ontario (CSAO) in a report on a series of tests they conducted that uncovered significant problems in using GFCIs on portable generators. While the CSAO conducted their tests to determine the effectiveness of GFCIs used on portable generators in typical construction scenarios, their findings are equally applicable to motion picture and event staging production applications (for a more in depth discussion of the problem, how to correct it, and a link to the CSAO’a complete report use this link: http://www.screenlightandgrip.com/html/emailnewsletter_generators.html#anchorElectrical%20Hazard%20Protection (http://www.screenlightandgrip.com/html/emailnewsletter_generators.html#anchorElectrical%20Hazard%20Protection))

In the OP's situation, I would much prefer to use the house power, even with the potential trip hazard, because I am assured that a EGC and Neutral bond at the main service panel and an intact EGC will cause over current protective devices and GFCIs to operate reliably.

Guy Holt, Gaffer
ScreenLight & Grip
[email protected]
Title: Re: AC Power for small outdoor event
Post by: kel mcguire on September 02, 2014, 04:31:33 PM
it's probably a good idea to visit the site, scope out where the band will be, and where the power is. I rent the Honda EU series all the time. Love them. Quiet. I bought the Honda parallel kit and sometimes will rent two 2k or 2 x 3k EUs. United Rentals usually has a deal; pick up friday after 3pm, and you get Sunday free if you're back by 9am monday. Typical is around $40 for the 2k, $60 for the EU3000. the 3000 has two versions, the electric start has a bit more headroom. You can also find 10ga, 50 and 100'  extension cords that come in handy.
Title: Re: AC Power for small outdoor event
Post by: Justin Schack on September 10, 2014, 02:37:33 PM
I want to thank everyone again for sharing the great advice and expertise. I think we've come to a resolution - the organizers have a 5500-watt inverter generator. Not sure the brand but I'm thinking that pretty much ensures safe, clean power for us.

Last question, though: The length of my Furman power strips is likely not long enough to run from the genny to where we'll need juice on "stage." I'm guessing we'll want to have the genny not right on top of us so the noise doesn't drown us out. What gauge of extension cord should I be using to run from the generator to my strips?

Thanks!
Title: Re: AC Power for small outdoor event
Post by: g'bye, Dick Rees on September 10, 2014, 02:59:46 PM
I want to thank everyone again for sharing the great advice and expertise. I think we've come to a resolution - the organizers have a 5500-watt inverter generator. Not sure the brand but I'm thinking that pretty much ensures safe, clean power for us.

Last question, though: The length of my Furman power strips is likely not long enough to run from the genny to where we'll need juice on "stage." I'm guessing we'll want to have the genny not right on top of us so the noise doesn't drown us out. What gauge of extension cord should I be using to run from the generator to my strips?

Thanks!

Don't just take their word for it.  Get brand and model and check it out thoroughly.  There's a very large range of quality in inverters.  Some are total crap.

As to the cabling issue: 

You not only need the proper gauge, but it should be proper "event rated" cable, SO, SOOW or such.  All cables should be full length, no intermediate connections or splices.  12 gauge minimum, larger if the distance is over 75 feet.
Title: Re: AC Power for small outdoor event
Post by: Justin Schack on September 12, 2014, 09:09:43 AM
Thanks. I asked. Good news: it's a Honda 6500iS.
Title: Re: AC Power for small outdoor event
Post by: Mike Sokol on September 12, 2014, 09:58:57 AM
Thanks. I asked. Good news: it's a Honda 6500iS.

+1 on that genny. Plus it's quiet enough that you can park it close to the stage and not hear it. Really...

Make sure you orient it so the exhaust points away from the stage. One time when I was getting a little exhaust blow-back I just stuck a box fan by it to waft the fumes away from the stage. Worked great and cost me nothing since I always throw a few box fans in the truck for outside shows. Playing in the sun can get a little warm and the artists really appreciate the breeze. Plus it makes your hair look good.  ;D

I'm double-checking with Honda, but I believe this is a floating neutral generator. If that's the case, you'll probably want to make a Neutral-to-Ground bonding plug, then bond the generator's grounding lug to a ground rod. Make sure you check with the utilities before you start pounding sharp metal objects in the ground. Or better yet, get the stage installer or whoever is delivering the generator to drive the ground rod before you get them. But don't bet on that happening. Hah!  >:(

Also, note that this particular generator has a 120-volt only or 120/240-volt mode set with a voltage switch, so you'll need to check out the distro connections. See page 16 on the manual at http://cdn.powerequipment.honda.com/pe/pdf/manuals/31Z25600.pdf

I believe that for your setup, you'll probably just run in 120-volt mode and maybe pull power from the 30-amp twist-lock for your stage amps and use the 20-amp duplex outlet for backline and mixer power. At least, that's how I would do it if I didn't have a 2 leg distro available that would connect to the 120/240 twist lock receptacle.

I know a few of you forum guys have a similar generator. How would you hook it up?
Title: Re: AC Power for small outdoor event
Post by: g'bye, Dick Rees on September 12, 2014, 10:17:44 AM
Congrats on the Honda.

Use two 12 gauge cables from the Hubbel outlets to get power to the stage if you don't have access to a proper distro with a twist lock connector. Two cables will help insure you experience minimum voltage drop over distance.  With that unit you shouldn't have to be more than 50' from your stage.
Title: Re: AC Power for small outdoor event
Post by: Mark Cadwallader on September 12, 2014, 10:39:30 AM
Mike, what do you recommend to identify the Neutral-Ground bonding plug?  Is there a standard color for identifying that device?  In the absence of a standard, I would probably use orange e-tape and a Sharpie to mark the plug. Mark C.
Title: Re: AC Power for small outdoor event
Post by: Mike Sokol on September 12, 2014, 11:01:28 AM
Mike, what do you recommend to identify the Neutral-Ground bonding plug?  Is there a standard color for identifying that device?  In the absence of a standard, I would probably use orange e-tape and a Sharpie to mark the plug. Mark C.

I generally use yellow or orange e-tape and a sharpie. My video shots show me with a P-Touch label on a G-N bonding plug, but I don't think that's rugged enough for live sound use. I usually mark it "G-N Genny Bond" or just "G-N Bond". Even if somebody is stupid enough to plug it into an already bonded receptacle, it's not the end of the world (as long as the bonded receptacle is properly wired itself). Double neutral bonds allow return current to flow in the EGC (safety ground wire) which will make any GFCI in the path trip. And, of course, the EGC should only carry ground fault current, not neutral current.
Title: Re: AC Power for small outdoor event
Post by: Guy Holt on September 12, 2014, 07:19:04 PM
I'm double-checking with Honda, but I believe this is a floating neutral generator. If that's the case, you'll probably want to make a Neutral-to-Ground bonding plug, then bond the generator's grounding lug to a ground rod.

If by “Neutral-to-Ground bonding plug” you mean what’s pictured below, an Inspector might have an issue with it.  Bonding 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. Article 250.4 (5) "Effective Ground-Fault Current Path," of the 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...."

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

An Edison Plug end jumper (like the one pictured above) that is rated for no more than 15 Amps clearly does not meet the requirement to “capable of safely carrying the maximum ground-fault current.” And, it is not permanent (I have had Inspectors kick my grounding clamp on hydrants to see if they are secure.)

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

In open frame generator 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.

Guy Holt, Gaffer
[email protected]
www.screenlightandgrip.com
Title: Re: AC Power for small outdoor event
Post by: Stephen Swaffer on September 12, 2014, 08:36:13 PM
The maximum ground fault "likely to be applied" in a setup using several 20 amp circuits is 20 amps.  For many years a #14 AWG was acceptable fr a 20 amp circuit, but no longer.  Given that the actual construction of a 15 amp receptacle is virtually identical to a 20 amp receptacle, I am fairly confident it would handle the overload long enough to clear a fault.

The lack of a permanent bond has always been what troubles me about this solution; however, on a rental or borrowed genny that the owner is likely to take exception to non-service center modifications a ground-neutral bond that is not technically code compliant seems better than no bond at all, does it not?

Maybe an off wall suggestion, but perhaps a bit of clear silicone might be in order to ensure that the bonding plug doesn't vibrate out and will actually take some effort to remove-reasonably easy to clean off when done.  Nearly every breaker panel manufactured has a ground-neutral bond that can be removed in under 10 seconds with a straight screwdriver.

 
Title: Re: AC Power for small outdoor event
Post by: Frank DeWitt on September 12, 2014, 09:09:06 PM
OK each 1/2 of the duplex outlet is fused for 20 amps so run the band from them.  That means that the maximum ground fault "likely to be applied" is 20 amps so make a neutral to ground plug using the 30 amp twist lock connector and you are all set.  The Twist lock is unlikely to fall out.

Nothing is permanent.
Title: Re: AC Power for small outdoor event
Post by: Mike Sokol on September 12, 2014, 09:34:04 PM
An Edison Plug end jumper (like the one pictured above) that is rated for no more than 15 Amps clearly does not meet the requirement to “capable of safely carrying the maximum ground-fault current.” And, it is not permanent (I have had Inspectors kick my grounding clamp on hydrants to see if they are secure.)

While I agree that a more permanent bonding solution would be preferred, most generator rental houses supplying the smaller inverter generators won't appreciated any modifications, and really don't understand the bonding issue anyways. This is especially true for RV owners who buy and use the Honda EU2000 generators by the thousands, then discover they won't power their RVs through an EMS surge protection system. And while the twist-lock G-N bond would be preferred to the straight blade plug, most of the time that's already being used for distro or RV power. I'm confident that a 1" length of #12 wire on a NEMA 5-15/20 plug would be able to sustain enough ground fault current to trip off the breaker or circuit protector on any of these small generators in the event of a short. But I do like the idea of a little silicon cement as a vibration fix.

Now once you start combining 6,500 watt Honda generators to make a 100-amp service for movie lights that's a different animal and will likely require a permanent G-N bond to pass inspection. But remember we're talking about smaller generators for outside music stages with much less fault current capabilities than what's typically used on a movie set.
Title: Re: AC Power for small outdoor event
Post by: Frank DeWitt on September 12, 2014, 11:29:59 PM
And while the twist-lock G-N bond would be preferred to the straight blade plug, most of the time that's already being used for distro or RV power. I'm confident that a 1" length of #12 wire on a NEMA 5-15/20 plug would be able to sustain enough ground fault current to trip off the breaker or circuit protector on any of these small generators in the event of a short. But I do like the idea of a little silicon cement as a vibration fix.

In the case of this generator there are two twist locks so a RV user could still put a neutral / ground connect plug in the other one.

In a case where there is only one, the RV user can use two neutral / ground connect plugs one in each half of the duplex outlet.  I agree, it is not necessary but it answers some of the code issue. 

I contend that a electrical inspector that wants to can find a reason to shut down anything including a hiker carrying a flashlight.
Title: Re: AC Power for small outdoor event
Post by: Jonathan Johnson on September 13, 2014, 01:07:04 AM
I contend that a electrical inspector that wants to can find a reason to shut down anything including a hiker carrying a flashlight.

If that hiker is under 18 years old and being paid for the job, then yes. That flashlight is a power tool, and minors aren't allowed to use power tools on the job.

But you CAN give them an 18" long, razor-sharp knife and send them out to shear a field of Christmas trees.  ::)
Title: Re: AC Power for small outdoor event
Post by: Guy Holt on September 13, 2014, 09:47:29 AM
I believe that for your setup, you'll probably just run in 120-volt mode and maybe pull power from the 30-amp twist-lock for your stage amps and use the 20-amp duplex outlet for backline and mixer power. At least, that's how I would do it if I didn't have a 2 leg distro available that would connect to the 120/240 twist lock receptacle.
 

In either of these scenarios, the largest fault current could be 27.5A so I like Frank DeWitt’s idea of a 10Awg jumper bridging the ground and neutral of whichever twist-lock receptacle is not in use. Now that we have established a low impedance path via the bond and ground rod for fault current to travel back to the generator’s windings, will it necessarily trip the breaker and clear the fault?  Say the extension cord being handled has a nick and the handler comes into contact with the bare copper of one of the current carrying conductors with one hand while holding onto a metal chain link fence post with the other. How much fault current will there be and will it trip the breaker?

If you don’t know how to answer this question I would suggest you use this link - http://www.screenlightandgrip.com/html/481_GFCI_Workshop.html (http://www.screenlightandgrip.com/html/481_GFCI_Workshop.html) - and read the summary of my IA workshop on ground fault protection – the life you save could be your own.

Guy Holt, Gaffer
ScreenLight & Grip
[email protected]
Title: Re: AC Power for small outdoor event
Post by: Frank DeWitt on September 13, 2014, 11:15:02 AM
In either of these scenarios, the largest fault current could be 27.5A so I like Frank DeWitt’s idea of a 10Awg jumper bridging the ground and neutral of whichever twist-lock receptacle is not in use. Now that we have established a low impedance path via the bond and ground rod for fault current to travel back to the generator’s windings, will it necessarily trip the breaker and clear the fault?  Say the extension cord being handled has a nick and the handler comes into contact with the bare copper of one of the current carrying conductors with one hand while holding onto a metal chain link fence post with the other. How much fault current will there be and will it trip the breaker?

If you don’t know how to answer this question I would suggest you use this link - http://www.screenlightandgrip.com/html/481_GFCI_Workshop.html (http://www.screenlightandgrip.com/html/481_GFCI_Workshop.html) - and read the summary of my IA workshop on ground fault protection – the life you save could be your own.

Guy Holt, Gaffer
ScreenLight & Grip
[email protected]

The answer is no.  But now that a connection has been established between the neutral and ground, the generator will work with an RV and the GFCI in the RV will work

In a portable sound setup there should be a connection between the generator frame and a good ground. (Ground rod. Hydrant stage platform) etc.  (if the stage platform is metal and not a good ground then it needs to be grounded.)  now a distro with a GFCI can be used.

BTW My humble little 1947 Antique light plant running a bunch of antique porcelain fixtures and two prong outlets, has a GFCI outlet installed, and tested.
Title: Re: AC Power for small outdoor event
Post by: Stephen Swaffer on September 13, 2014, 02:23:00 PM
A larger ground is always better, but given that #12 AWG is actually rated to handle 25 amps with a 90 deg C insulation continuously, I seriously doubt it will vaporize in the time it takes a breaker to clear a 27.5 amp fault.  I am taking a break from pulling wire for a 400 amp circuit-likely fault current is 400 amps-required ground is #3 AWG-with an ampacity somewhere around 100 amps.  Fault handling capacity is a completely different consideration than ampacity which is primarily determined by the temperature rating of the insulation.

I would consider the NEC required size for an EGC to be a good guideline for a bonding conductor-#12 with breakers up to 20 amps, #10 up to 60 amps.
Title: Re: AC Power for small outdoor event
Post by: Jonathan Johnson on September 15, 2014, 06:11:13 PM
Getting back on topic, read here for another PSW member's experience with borrowing power from far-flung sources:

http://forums.prosoundweb.com/index.php/topic,151439.msg1388846.html#msg1388846
Title: Re: AC Power for small outdoor event
Post by: Mark Cadwallader on September 15, 2014, 06:57:17 PM
I made a N-G bonding plug this weekend with a Hubbell 5-15P and some 10 AWG  THHN wire, in case I need one for a small Honda generator someday. Orange e-tape and a sharpie....  Mark C.
Title: Re: AC Power for small outdoor event
Post by: Guy Holt on September 22, 2014, 06:57:31 PM
Getting back on topic, ...

No one wants to take a stab at what the fault current will be in the scenario I described above? Again, the scenario is someone is handling a cable with a nick in the rubber jacket.  If, because of the nick,  they come into contact with the bare copper of one of the current carrying conductors with one hand while holding onto a metal chain link fence post with the other, how much fault current will travel through their body?  IMO this question is very much on topic.  Since the OP is designing an electrical distribution system that the public can come in contact with, he should understand why he needs GFCI protection. An individual in the scenario described above will go into ventricular fibrillation (arrhythmic heartbeat) after .8 seconds. How much current will kill you that fast?  I labored for years as a film set electric under the false impression that the breakers on our distro boxes were there for my protection.  It took a bit of a shock to learn that they were not.

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

Title: Re: AC Power for small outdoor event
Post by: Mike Sokol on September 22, 2014, 10:34:33 PM
No one wants to take a stab at what the fault current will be in the scenario I described above?

Assuming the human body has approximately 1,200 to 1,500 ohms hand-to-hand resistance (with moist hands) and 120 volts AC exists between the current source (nicked wire) and sink (grounded chain link fence) then there will be around 80 mA to 100 mA fault current through the victim in such a scenario. Just 10 mA of current is a very painful shock. 20 mA is enough to overcome your hand release reflex so you can't let go of an energized wire. And 30 mA for more a few seconds is considered to be enough to cause ventricular fibrillation in a large portion of the population with old people and young kids being most at risk. Without intervention with a defibrillator, you could be dead in minutes depending on your heart condition to begin with. An 80 to 100 mA hand-to-hand or hand-to-foot shock for more than a few seconds is considered lethal in most cases. A lot of the danger depends on if the fault current travels through the chest cavity or not, so a finger-to-finger shock on one hand is not dangerous to the heart, but if sustained long enough will cause long-term nerve damage in the hand.

So no, a human's internal body resistance won't produce enough fault current to trip even a 15 amp circuit breaker. 

The over-current circuit breakers in a generator, or any other service panel, are only there to protect the downstream wiring from overloading and heating up enough to cause a fire. They are NOT there to protect your gear from over-current damage (that's the job of the internal fuse) and certainly not there to protect a human from being electrocuted.

On the other hand, The 6 mA trip point of a standard domestic GFCI has been designed to stop any high-resistance shock that approaches danger levels, even for sustained contact. There are commercial/industrial GFCIs that have adjustable threshold points up to 30 mA, which is right at the level of lethality for sustained contact. These were originally designed for mines and such that had a lot of moisture in the motors that would trip a 6 mA breaker too often. Of course, a low-impedance fault of an ohm or so (typical stage wiring) will produce up to 100 amps of fault current which should clear any stage breakers. Of course, once you get to camlock current levels of 100 or more amps, then arc flash danger becomes the main concern. I believe that all personnel handling potentially live camlocks should be wearing PPE gear because the resultant arc flash of a 200 amp camlock connecting to a cable that was shorted to the same fence could produce a significant fireball that would be very dangerous even from several feet away. So for low-voltage hookups (under 600 to 1,000 volts as defined by the NFPA) the arc flash energy available must be closely monitored.
Title: Re: AC Power for small outdoor event
Post by: Stephen Swaffer on September 23, 2014, 11:03:19 AM
Of course the "if....s" can be endless-but another aspect of this is that if the cord is pulled pver/through the fence it would be possible for a damaged cord to energize the fence, unless it is bonded it would be questionable if a 15A breaker would trip.  To me from an electrical standpoint, especially at outdoor events fences pose a quandry-with metal poles they will be well grounded, but its hard to really argue that they need to be bonded.  I would use extra caution with power wring around them.
Title: Re: AC Power for small outdoor event
Post by: Jerome Malsack on September 23, 2014, 11:48:08 AM
A metal pole in the ground is not always considered a good ground and could be encased in concrete reducing the grounding ability. 

That is why antenna masts are not considered grounded by the mast poles and the foundations. 
Title: Re: AC Power for small outdoor event
Post by: Stephen Swaffer on September 23, 2014, 12:55:17 PM
I suspect that has more to with RF than power grounding.  All new construction in Iowa with a concrete footing is required to use a "Ufer" ground-formally know as a "concrete encased electrode"-because it is a superior ground to a grounding rod-at least that is what the experts claim-I just do what the AHJ tells me I have to to pass!  It would not surpise me to be told that a Ufer ground does not work as well with RF.
Title: Re: AC Power for small outdoor event
Post by: Justin Schack on September 23, 2014, 02:17:37 PM
So in case anyone cares about how this actually went, the block party was Saturday and all went off swimmingly. The only little hiccup I had was that the various power cords on some of my equipment were not long enough to reach my two Furman power strips without using — ugh — extension cords. Exactly what I wanted to avoid in the first place, but it was just three fairly short extension cords running from powered speakers and a bass amp to the bricks, which were connected to the 120V outlets on the Honda inverter (instead of hundreds of feet of extension cord from a wall outlet in someone's home). Next time I'll invest in some longer AC cords so we won't have to use the extension cords.

I did notice I got more 60-cycle hum out of my guitar amplifier when using my single-coil Fenders than when I do at home, but it was nothing out of the ordinary. And other than that there were no noise, power or other issues. The generator was quiet enough that we had it stationed about 10 feet away from the drummer without it being too loud for us to hear what we needed to hear. We did not ground it, however. It was out on the street behind where we set up. I know later in the thread there was some talk about grounding the genny, but I also remember back to early in the thread when someone — I think it was Mike — said that tons of events have gone off just fine with an ungrounded genny as the power source.

Thanks again to everyone for their thoughts and advice. Much appreciated.
Title: Re: AC Power for small outdoor event
Post by: Stephen Swaffer on September 24, 2014, 06:58:30 PM
It was out on the street behind where we set up. I know later in the thread there was some talk about grounding the genny, but I also remember back to early in the thread when someone — I think it was Mike — said that tons of events have gone off just fine with an ungrounded genny as the power source.

Thanks again to everyone for their thoughts and advice. Much appreciated.


Glad to hear that things went well!

Not to beat you up-but let me play devils advocate for a minute.  While it may be true that tons of events (including yours) have gone off just fine with an ungrounded power source-the same could be said for ice bucket challenges-but I have heard about several lately and the ones we (and the press gives free advertising to) hear about are the ones gone wrong.

Who made the decision not to ground the genny?  Doesn't matter much to anyone now-but it would be a very important question HAD something gone wrong.  If your name was the answer to that question, would you want to explain to a courtroom-or to a friends family, "so and so said online that lots of events have gone off fine with an ungrounded genny."

Just trying to get the wheels turning-I certainly can't look you in the eye and say I have always done things the right way myself.