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I recently had some electrical work done on my home to bring it up to code - there was no GFCI protection in the kitchen or bathroom when we bought the house, so our electrician fitted GFCI breakers at the panel. He did not use the GFCI outlets because he explained that our existing outlet boxes were too small to fit the extra size of a GFCI.

When I plugged in my generator to my transfer switch though, and flipped the main breakers in the transfer switch from LINE TO GEN, the GFCI breakers in my main service panel immediately tripped.

I have read that this may have something to do with the fact that most portable generators come with the ground + neutral bonded to the frame. Apparently, this makes the generator a SDS (separately derived system) compliant with OSHA for use on job sites. I can confirm that my generator is like this. It says so right on the power panel.

However, when connecting to the house, I have heard that the ground + neutral are actually already bonded together in the panel, so you should "float" (disconnect) the neutral wire at the generator. However, I have also heard this increases shock risk on the generator side.

I am not positive that this is why the GFCI breaker in my main panel is tripping, but it's a hunch. It could just be that the breaker doesn't like the power signal coming from the generator.

Regardless, I'd still like to have power to my kitchen from the gen.

Any suggestions as to why this could be happening?

  • Additional info: The generator has four 120V GFCI receptacles. It also has an L14-30R 30A twist lock connector that I use to power the house - however, this receptacle does not appear to be GFCI protected. – rk15000 Jan 18 '18 at 15:08
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    You haven't given us enough information about how the circuit is configured. Particularly we'll need a lot more about the generator transfer switch. Neutral at the generator needs to be part of rhe circuit. You have more flexibility whqt to do with ground. – Harper Jan 18 '18 at 15:54
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That's to be expected. The neutral from the circuit is going through the GFCI breaker, but the hot is coming from the generator. The GFCI sees this as an imbalance, since there's no current flowing through the hot side of the breaker.


Here's what your setup likely looks like (if it was drawn really quickly in MSPaint).

Bad MSPaint Generator Transfer Switch diagram

If you follow the current through from the generator, you'll see that it returns through the GFCI breaker.

Bad MSPaint Generator Transfer Switch diagram showing current flow

However, since the current is not flowing through the "hot" side of the breaker. The breaker sees an imbalance, and trips.


The cutaway in this image shows the internal circuitry of the GFCI breaker, and depicts the current flowing only on the neutral wire.

Bad MSPaint Generator Transfer Switch diagram showing current flow and CT in breaker


WARNING:

If the generator or transfer switch does not provide GFCI protection, the kitchen will not have GFCI protection when on generator power.

  • Thanks for the detailed drawing. So based on what you know, what is the least risky option? To let the breaker trip or remove the neutral bond on the generator? I can't imagine the transfer switch provides GFCI protection (it seems kind of old) - the only outlets on the genny that appear to be GFCI protected are the 120V, not the 240V. So i would imagine that yes, my kitchen is powered but not protected via GFCI anymore when on generator power. – rk15000 Jan 18 '18 at 17:58
  • @rk15000 Removing the neutral bond on the generator will not change anything. – Tester101 Jan 18 '18 at 19:10

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