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Discussion Starter · #1 ·
My buddy is having wedding this weekend where they are using a portable generator to power some lighting and audio equipment. He was told that since there will be audio equipment on the generator they will need to ground the generator to eliminate hum. I have never had problems with this in the past and know that the code doesn't require a grounding electrode, just that the neutral be bonded to the frame of the generator. They will just be running a few cords from the generator and I have never seen a portable gen that the EGC doesn't land on the frame.

Has anyone ever run into problems like this before?
 

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Nope and I have done lots of mobile audio work. Whoever told him grounding the generator is necessary to avoid hum is either full of it or doesn't know how to properly connect audio gear.

Think about it for a moment...a portable generator is technically an isolated SDS so how will grounding it help eliminate hum? :rolleyes::no:

Some important things to note though:

1: DO NOT use a cheap generator. ONLY use a true sinewave, well regulated generator (Like Honda's inverter generator line.) NO Harbor Freight specials or other low-end generators.
2: DO NOT mix gear connected to the generator and "shore power" unless you bond the grounds together!! you MUST bond the grounds or hum will be the least of your issues.
3: If possible, do not power ANY lighting gear from the same generator, especially anything on dimmers or computerized lighting. You can have noise issues, and the computerized gear won't like the voltage swings caused by the audio gear when it is cranking...
4: Make sure the generator has at least DOUBLE the running AC input watts capability of ALL of the gear being powered. Audio gear (specifically amplifiers) running at high levels WILL create a lot of high-current spikes in response to the audio program (think thumping bass especially) which WILL make the generator unstable if it doesn't have enough capacity.


All of that makes it sound worse than it is, but it really isn't bad..but at events like a wedding, you do not want to take the slightest risk of problems or you will face the wrath of bridezilla. :laughing:
 

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Discussion Starter · #4 ·
Slick,

All good advice. I have set up lots of these before as well, and never had a problem. I used to set these things up for several outdoor event spaces with way more electronic equipment, lighting boards, and sound stuff than they are using. Their only running Christmas lights, no dimmers. I will call and get the generator model and check to see how the voltage is regulated.

I would guess they have enough wattage with 52 kw, but I don't know for sure since I am not sure about the equipment. Just they are having some bands play, but I talked with the sound guy for my friend and he hasn't ever had problems with portable generators either.

I had originally thought the sound guy said it needed to be grounded, but it was some one at a rental company.

Anyway thanks for the input and yes I have seen plenty of brides I wouldn't want to cross.
 

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Discussion Starter · #5 · (Edited)
Went and looked at the generator on the way home one GFCI 20 amp Recpt. 3x 50 amp 125/250v Recpts. Three prong. If I actually needed to come of those with a load center what would I do about the EGC from others equipment?
 

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Went and looked at the generator on the way home one GFCI 20 amp Recpt. 3x 50 amp 125/250v Recpts. Three prong. If I actually needed to come of those with a load center what would I do about the EGC from others equipment?
Was it a 52kw? or 25kw or so? Most of the generators in that size class I have used have lugs for the outputs available as well, for connection to a "distribution box" (fancy show name for a portable breaker panel.)

Now, in the size class of what I like to call "commercial" generators (usually 15kw and up) the rental guy IS correct, you will need to drive a ground rod at the generator location and bond it to the neutral lug (if the generator has lugs for its output, as I expect one of this size class to have) or to the generator's designated ground lug. (Which may mean the generator is internally bonded neutral to ground.)

As for the 50amp receptacles and grounding...depending on the receptacle type there IS a ground conductor connection..the metal shell if it has a "pin and sleeve" housing around the twistlock current carrying connections. (I forget the NEMA type offhand..) I'll try to find it online and post a pic later.

If it is just a run of the mill twistlock or NEMA flat prong setup...I think the correct way would be for you to have a separate EGC running back to the generator.

I am thinking that it would be the first type I described..which is also the same type of twistlock 50a that jobsite spider boxes use...which do have an EGC in the cabling so the recepts in the spider box would be properly grounded.

If you have a link to the rental place and the generator in question I could give more specific advice.
 

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Discussion Starter · #7 · (Edited)
Yes, it's a 52 Kw Atlas Copco QAS 58JD. I didn't see lugs on it, but I could have missed a door. I am trying to find some more info now and really appreciate the help. I am wondering if it wouldn't be a wise idea to rent a distribution box. The Rental place is http://www.appequipmentsupply.com/

I'm editing this because it looks like there is a panel I missed with lugs, there wasn't a ground lug were the info I found said, but I can fix that. Still wondering what the easiest way to proceed would be here. Perhaps this is a bit of over kill.
 

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Discussion Starter · #9 ·
Thanks for the help I found a rental place that has a distribution panel for $28 for the weekend. Kind of a no brainer and I finally found out what type of equipment and voltages were needed. I was making it over complicated.
 

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Thanks for the help I found a rental place that has a distribution panel for $28 for the weekend. Kind of a no brainer and I finally found out what type of equipment and voltages were needed. I was making it over complicated.
Be SURE you test everything out days ahead of time so you can respond to any "issues"!

RC
 

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Discussion Starter · #11 ·
Yeah that would have been nice, but I just found out yesterday and the wedding is on Saturday. I was just supposed to be in the wedding. Now I am just helping out a friend. I am going to spend the evening over there tomorrow and test every thing out. One of the colleges I used to do work for would be setting up the event at the same time as it was starting so this might bring back some less than fond memories.
 

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One more thing. The Rec. are 125/250v 50 amp three prong which I think are NEMA CS6365. If I am understanding right, I would need a separate EGC? Because they don't have a metal ring around them.

Thanks Again
Take a look at the picture and info in this link:

http://www.cesco.com/b2c/product/41...1_a_7c414442&gclid=CI_0qKuDgsACFSpo7AodXSEAfA

The grounding is accomplished with the metal inner liner on that plug which will mate with a shell (or often) a metal tab on the outside of the receptacle.



Best that you found a rental of the distribution box too as they will (should) have the grounding connected properly with the included cabling.

I would meter it after power-up just to be safe. :)
 

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Discussion Starter · #13 ·
I will meter everything after power up, especially since it's rental equipment. I do have one of those plugs in my shop, some spare SO and an Main lug panel if some one does end up needing 240v. Had to do some digging though. Also glad that I found a distribution panel as it saved some work on an already busy weekend.

Again thanks for the help. When I used to do service work I used to remember that you should only let the customers side only be a small part of the story. I let this one take me on a bit of a ride worrying about the wrong things. Thanks for great advice.
 
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