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Old 07-01-2009, 03:10 PM   #1
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GFCI on generator tripping; home backup


I just had an electrician wire my house with an interlock kit so that I can use my new 6600 watt generator for power backup. Unfortunately, the GFCI in the generator's panel trips as soon as I attach the cable to the house. My electrician says that there is absoultely nothing wrong with the wiring in my house and that the problem is with the GFCI. He says that most generators with built in GFCI's won't work for power backup. He also says that there is no way he'll touch the generator to disable the GFCI for liability reasons. How do I use this brand new $2,200 generator to power my house if the GFCI keeps tripping and can't be disabled? Thanks in advance for the advice!

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Old 07-01-2009, 04:57 PM   #2
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GFCI on generator tripping; home backup


http://159.105.83.167/Portals/0/WP%2...tandards22.pdf

?

BTW, 900' of perfectly good Romex will probably have enough inter-conductor capacitance to give you 4 mA of reactive leakage current and so would validly trip a GFCI.
If it is the Romex the fix would be to have the gen. only run sections or only specific appliances/fixtures in your house.
I suppose you could check this by running the generator with almost all breakers off in your house. Turn them on one by one until you trip the GFCI. If the thing trips with all breakers off the problem almost certainly has to be elsewhere.

You could also check the leakage current of the wiring in your house. Put a 7-1/2w incand. lamp in series with the ground wire that serves the cable downstream of your GFCI. If the voltage across the bulb reads from 0.6 vac to up to 120vac you've found your leakage path to ground. A normal reading would be less than 15 mVac. Disconnect chunks of the cable or appliances until the leakage current goes away.


Last edited by Yoyizit; 07-01-2009 at 05:30 PM.
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Old 07-01-2009, 05:25 PM   #3
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GFCI on generator tripping; home backup


The problem of GFCI tripping is that the service panel that you are backfeeding already has its neutral conductor bonded to the grounding conductors.

If these conductors are separately monitored by an integral GFCI device in the generator, it will trip out as soon as you plug it in, even with the interlocking breakers switched off.

Some generators have instructions on how to configure when used as a stand-by power source for a home.

What brand and model number are you dealing with here?
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Old 07-01-2009, 05:53 PM   #4
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GFCI on generator tripping; home backup


Are you saying the 120v GFI is tripping?
If you are trying to connect your panel to the 120v 20A receptacle on a generator this is a VERY flawed plan. You should be using the 120/240v receptacle on your generator which is not GFI protected.
Your electrician should have know this.
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Old 07-01-2009, 06:31 PM   #5
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GFCI on generator tripping; home backup


As stated above, almost certainly the generator neutral is bonded to the ground. So is the house. You'll need to remove the bond jumper in the generator.

Also as stated above, it'd be a huge waste of generator capacity to use a 120 volt receptacle to power the house. You can only get 2400 watts through a 20 amp 120 volt receptacle.

Some generators have two pole GFIs though, if the cord that plugs into the generator has 4 prongs on it, then it'll deliver full power to the house. But you'll still need to remove the bonding jumper.

In no case remove the bonding jumper at the house panel. If you do, you'll have no ground-fault protection when on utility.

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Old 07-01-2009, 06:52 PM   #6
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GFCI on generator tripping; home backup


Quote:
Originally Posted by Yoyizit View Post
http://159.105.83.167/Portals/0/WP%2...tandards22.pdf

?

BTW, 900' of perfectly good Romex will probably have enough inter-conductor capacitance to give you 4 mA of reactive leakage current and so would validly trip a GFCI.
Did I miss something?
Where does it say the Gen is 450' away from the house?
That would be 3 houses away for me
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Old 07-01-2009, 07:09 PM   #7
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GFCI on generator tripping; home backup


Thanks everyone for the quick replies. The generator is a Wacker Neuson GPS6600A and I'm using the 12/240v receptacle.

I posted here because I wasn't hearing from the manufacturer. Wouldn't you know, they just replied tonight. Looks like bond or ground jumper is the issue. Below (in italics) is the reply I got from Wacker Neuson.

Thanks for the guidance. It looks like I'm on track now.


The neutral - ground jumper wire on the generator will have to be
removed to prevent the nuisance tripping of the GFCI.

Your house should already have its neutral bonded to ground so this
still meets requirements of the National Electric Code (NEC).



Your Wacker Neuson dealer can sell you a kit p/n 0164835 that contains
these instructions and stick-on labels that warn the generator now has a
floating neutral.



NOTE: If you ever disconnect the generator from the house and use it for
other purposes, you MUST re-connect the neutral - ground jumper on the
generator!

If you (or the next owner of the generator) do not intend to re-connect
the generator to the house again... then you may also remove the
floating neutral labels.
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Old 07-01-2009, 07:18 PM   #8
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GFCI on generator tripping; home backup


Exactly how many generators has this guy wired to not know there is a neutral-ground bond that needs to be removed in the generator. I just don't get it.
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Old 07-01-2009, 07:28 PM   #9
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GFCI on generator tripping; home backup


Quote:
Originally Posted by Scuba_Dave View Post
Did I miss something?
Where does it say the Gen is 450' away from the house?
That would be 3 houses away for me
Nah, I think the average house has more than 900' of Romex in it and all that distributed capacitance adds up.
I'm going to fire my ghostwriter!

To the OP: you know, there is an implied warranty of merchantability and an implied warranty of fitness. Your electrician must have known what your intention was in buying this generator. Your State's Attorney may persuade the guy to make this right.

Last edited by Yoyizit; 07-01-2009 at 07:33 PM.
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Old 07-01-2009, 08:22 PM   #10
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GFCI on generator tripping; home backup


In my experience, very few electricians know about neutral bonding of generators. This includes small home-style generators all the way up to huge ones that would run half a city.

Neutral bonding is not all that difficult; in the end there can be exactly one. No more, no less.

With a generator, if the transfer switch doesn't transfer the neutral, the generator cannot be neutral bonded. If it does transfer the neutral (rare, but required in some cases, like hospitals), then it must have its neutral bonded.

Very few people, even electricians with lots of experience, and a multitude of electrical engineers, understand this.

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Old 07-01-2009, 08:43 PM   #11
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GFCI on generator tripping; home backup


Quote:
Originally Posted by MrNeutron View Post
. . . 6600 watt generator for power backup.. . . How do I use this brand new $2,200 generator to power my house. . .
Did you really spend $2200 on a gas 6600 watt generator? Wow, someone made a profit.
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Old 07-01-2009, 08:47 PM   #12
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GFCI on generator tripping; home backup


Quote:
Originally Posted by AndrewF View Post
Did you really spend $2200 on a gas 6600 watt generator? Wow, someone made a profit.
Maybe it's not a piece of crap.
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Old 07-01-2009, 08:54 PM   #13
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GFCI on generator tripping; home backup


If its an 1800 RPM unit, worth every dime.
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Old 07-01-2009, 08:55 PM   #14
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Quote:
Originally Posted by kbsparky View Post
If its an 1800 RPM unit, worth every dime.
True, I didnt check the specs and would agree. If it is a 3600 RPM...then no.
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Old 07-01-2009, 11:21 PM   #15
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GFCI on generator tripping; home backup


I think it's sweet of the manufacturer to sell you a 'part' that contains nothing but instructions & labels!

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