Portable Generator Safety

K

Kip Conner

Junior
Mar 13, 2011
370
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0
Athens, GA
I have a show on a parking deck next week and the "pro" event planners aren't being real forthcoming about the power availability. I've tried to get phone numbers of the building's engineer several times and I'm afraid that they are going to give me some portable 6000KVA generator. I can make it enough power to by cutting some monitor mixes but my biggest concern is grounding.

It's similar to the generator on a boat problem. I'm uncomfortable with this power situation unless the generator is earth grounded. When I rent generators I use United Rentals and they install the earth ground for me. Since we are on a parking deck it's going to be pretty tough to this by way of the ground or a cold water pipe.

The band is backing me up 100% and they know that if I tell them it's not safe, they won't perform. It would be different if it was only playback music- but we are talking live microphones with electric guitars. Other than ground loops, I'm mostly concerned about electrocution.

I've explained to them that as of now I can't do it in good faith- but what demands would guys make? Seems like there needs to be a licensed electrician involved in this event to either make it safe or tell me it is safe.
 
Re: Portable Generator Safety

I thought I would see this email today...

"We’ve used these generators a number of times for musical acts..."

I hated to be the bearer of bad news but this Operations Director just got a schooling in generator usage and earth grounding. I gave him several options for grounding his system in a parking deck and used the word Licensed Electrician as often as I could. The good thing is that he was more than happy to make it right after I explained to him that anyone can become the ground on an ungrounded system, including his client who will probably want to make an announcement at some point during the reception.

 
Re: Portable Generator Safety

Let me get this straight, you were going to have 20,000 monitor mixes but you think you need to par it back to just 10,000 monitor mixes since you only think you'll have 6,000,000 watts of generator power available? If you don't know what to ask for, you never know what you'll get.

In my city, a generator under 25kVA does not need a generator permit nor does it need a ground rod if the ground is bonded to the frame. You need to contact your local authorites and find out what is required in your area.

You are more than likely making a whole lot out of nothing. You should however preview the venue as any pro production company would do then you'll know what is there and what isn't.
 
Re: Portable Generator Safety

I know what I need and what I asked for, the biggest issue is with the lack of communication between the band and the event planner. I just got drug in at the last minute by the contracted band to make sense of it all. They realized that they needed someone to take control. It took me 5 days to get the address of the parking deck from the event planners... and I will go down there in advance to measure clearances and see their rain plan. It's all very very sketchy. For instance, the rain plan is that they are going to move them to a covered part of the deck. We all know it will sound bad, but worse is that they trying to put the band at the bottom of the slope... with no stage so they will sit in the water run-off.

What's there is a parking deck roof. Nothing else. They are trying to provide with a generator that can't supply the power I NEED. So, I'm going to take a PA system that will fit on the power that they can supply. I need 4 20A circuits, they can provide 2 20A circuits. So they get a smaller PA than what we need, but I've done better with worse conditions.

As for the grounding of the generator, the OSHA standards say that I do not need to- however, my confusion is where it's being used- on a parking deck. So where does the ground come from when it's sitting on a concrete structure? That's the part I'm not sure. The code makes no mention of generator size... nor the use of your 20,000 monitor mixes.

My persistence with them is that I don't know what is correct and they don't either. So, to save us both some trouble, why don't they hire someone to come in and make sure it's right. Their poor communication doesn't give me confidence that they actually know... and I told them upfront that I don't know. What I do know is that there's a huge potential for severe injury if it's not done right. They are trying to save a buck, I'm trying to save a life.
 
Re: Portable Generator Safety

I found this interesting tidbit that helps answer my question.

"In a normal system, the Earth ground is not a point of current return. It serves no purpose for the normal operation of the electrical system. We have a "ground" wire that we run with our circuits, but this ground is connected to the neutral at the service. This allows for a path that fault current can return to the service neutral on and trip a circuit breaker. The Earth has nothing to do with it."

That being said they only way that there could be failure is if a) I wired a quad box wrong or b) the generator itself is wired wrong. I'm positive my power is all correct, I just need to circuit test the gennie's outlets for correct wiring and test that the resistance between the frame and the outlets measures at 0 ohms.

My biggest fear is that it's not my generator so I don't know it's history.
 
Re: Portable Generator Safety

Kip Conner said:
...but we are talking live microphones with electric guitars. Other than ground loops, I'm mostly concerned about electrocution.
Click to expand...

As long as the distribution is correct, with a single generator with a couple of outlets on it, then all the metalwork (including the generator frame) will be connected together through the ground wires. This'll be your system ground. This has nothing to do with "ground", the soil that we stand on, merely that the ground wiring in your cables will connect all the metalwork together. So you can't (without a fault condition happening) get a metal-to-metal (ie mic to guitar) shock.

The same thing will help prevent ground loops, as long as there is a single ground point, presumably in the generator behind the two 20A outlets they'll be giving you. If there is any doubt that the grounds of the two sockets provided are connected together, then a poor man's distro will make those grounds common and solid.

The issue remaining is the potential for shock from between your system ground to soil, to which you do not have a solid bond. RCDs (GFCI) breakers at the generator will guard against this as long as it is the generator that is the source of power of the potential shock.
 
You are confusing the two meanings/purposes of ground which depends which side of the neutral ground bond you are on.

On the stage side of the system the safety ground wire provides a direct path so if you loose the neutral, the current draw should pop the breaker. The worse case is if the hot energizes metal in the system. Bonding all the metal together provides the path so someone touching the metal doesn't become the return path.

The ground on the other side of the ground/ neutral bond serves two purposes; it provides lightning protection and serves as a local zero potential which is why a service should only have 1 bonding point.

I think the question of use is not quite as clear when you are using a generator because I read the codes to say that the deciding factor is whether you are using a distributed system or not. As far as I can tell if you are using the convenience outlets mounted on the generator you do not need a separate ground rod, however having one does no harm.

If you have a distributed system which means to me a higher current that is broken out to branch circuits with breakers that are not mounted on the generator then you need the ground rod.
 
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