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Author Topic: Generator question  (Read 30269 times)

Stephen Swaffer

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Re: Generator question
« Reply #30 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.
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Steve Swaffer

Stephen Kirby

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Re: Generator question
« Reply #31 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.
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Stephen Swaffer

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Re: Generator question
« Reply #32 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.
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Steve Swaffer

Stephen Kirby

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Re: Generator question
« Reply #33 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?
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Debbie Dunkley

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Re: Generator question
« Reply #34 on: September 16, 2015, 08:38:59 PM »

You guys are scaring me !!!
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A young child says to his mother, "Mom, when I grow up I'm going to be a musician." She replies, "Well honey, you know you can't do both."

frank kayser

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Re: Generator question
« Reply #35 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
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David Buckley

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Re: Generator question
« Reply #36 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.

« Last Edit: September 17, 2015, 12:24:37 AM by David Buckley »
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Stephen Swaffer

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Re: Generator question
« Reply #37 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."
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Steve Swaffer

Robert Lofgren

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Re: Generator question
« Reply #38 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.
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David Allred

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Re: Generator question
« Reply #39 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.

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ProSoundWeb Community

Re: Generator question
« Reply #39 on: September 17, 2015, 07:02:01 AM »


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