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Author Topic: Generator question  (Read 38142 times)

Mike Sokol

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Re: Generator question
« Reply #70 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.   

Mike Sokol

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Re: Generator question
« Reply #71 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.

TJ (Tom) Cornish

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Re: Generator question
« Reply #72 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.
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Guy Holt

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Re: Generator question
« Reply #73 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
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Guy Holt

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Re: Generator question
« Reply #74 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


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TJ (Tom) Cornish

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Re: Generator question
« Reply #75 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.
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Stephen Swaffer

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Re: Generator question
« Reply #76 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.
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Steve Swaffer

Jamin Lynch

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Re: Generator question
« Reply #77 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.
« Last Edit: September 23, 2015, 10:05:44 PM by Jamin Lynch »
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Rob Spence

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Re: Generator question
« Reply #78 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.


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David Buckley

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Re: Generator question
« Reply #79 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.

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Re: Generator question
« Reply #79 on: September 23, 2015, 10:21:19 PM »


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