Generator causing AFCI's to trip ...?

[brantmacga]

We still have many people here without power due to hurricane Irma.

One of my customers called me saying they had connected a generator to their home, and that most of the breakers are tripping. This is a new house I finished about 4 months ago.

I go out and find the owners father, who is a mechanical contractor in town had shut off the main breakers and back-fed the generator into the service. Everything is connected correctly.

Out of roughly 40 AFCI & AFI/GFI combo QO breakers, at least 25 are tripping instantly. Also one of the QO surge breakers is out. They are tripping across both lines. Voltage is normal.

Has anyone seen a generator as the source cause this issue? My other thought is that they took a power surge that damaged them, but I've never seen that happen. It may be next week before they get power and I know for sure.


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[GoldDigger]

Quick possibility is that there is a ground to neutral bond at the generator.
That means that any circuit protected by an AFCI breaker that includes ground fault (GF) detection might false trip even though a logical analysis will indicate that all of the neutral current for the circuit must still return through the neutral connected to the breaker.
Other possibility is that the generator is producing a waveform that mimics a series fault signature and the breakers trip whenever the load on their circuit goes above 7-8 amps.

 

[brantmacga]

There is a bond, but it's ahead of the breakers.

I too wondered about possible waveform problems, but I couldn't imagine the breakers are seeing it as an arc fault upstream. I wonder if there are voltage issues I don't see on my meter that are causing it.


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[GoldDigger]

There is a bond, but it's ahead of the breakers.

I too wondered about possible waveform problems, but I couldn't imagine the breakers are seeing it as an arc fault upstream. I wonder if there are voltage issues I don't see on my meter that are causing it.


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The AFCI breaker cannot tell whether the fault signature is coming from upstream or downstream. It can only tell accurately what the current on its own circuit is. That is why a spurious but strong series fault signature on one branch with a low current load can trip an AFCI breaker on another branch that has current above the series trip limit.

And if possible, I would try disconnecting the bond at the generator (or interrupting the EGC?) to see whether that helps. Stranger things have happened.

 

[brantmacga]

The AFCI breaker cannot tell whether the fault signature is coming from upstream or downstream. It can only tell accurately what the current on its own circuit is. That is why a spurious but strong series fault signature on one branch with a low current load can trip an AFCI breaker on another branch that has current above the series trip limit.

And if possible, I would try disconnecting the bond at the generator (or interrupting the EGC?) to see whether that helps. Stranger things have happened.

I didn't know that. So it does seem likely then it could be seeing a fault upstream.

We did take the EGC off and had the same problem.

Thanks


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[GoldDigger]

You took the EGC off, but was the generator neutral still earth grounded (local electrode)?

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[ramsy]

..I wonder if there are voltage issues I don't see on my meter that are causing it.

Power grid may be out, and main breakers off, but main-bonding still connects everyone's secondary system noise thru service neutrals.

Stand-alone generators, correctly installed or not, with possible leakage currents or noise, can propagate thru utility neutrals to trip your A/GFCI breakers.

Try lifting utility-side neutral ahead of back-fed breakers, but perhaps not ahead of main-bonding where electrodes get disconnected.
If lighting strikes are probable, opening your path to the grounding electrodes is not a good idea.

 

[retirede]

A couple thoughts:

Don't QOs indicate whether the trip was AF or GF?

Also, isn't there a minimum current flow needed befor AFCI function is active? If so, they have to be tripping on GF.

Agree that generator neutral to ground connection is suspect.

 

[Sierrasparky]

Is it possible the AFCI breakers are damaged?

 

[ptonsparky]

I tend to agree with Ramsey, lift the utility neutral. See what that does for you.

 

[qcroanoke]

I tend to agree with Ramsey, lift the utility neutral. See what that does for you.

I think you need to remove the neutral/ground bond in the generator.

 

[mbrooke]

Generator waveform is being mistaken as an arc fault to the breakers. Nothing more into it.

 

[mlnk]

There must be some unique problem with the generator. There are thousands of homes using generators especially during blackouts and they are all working OK , right?

 

[Sierrasparky]

For starters the Customer had just back fed the panel without a transfer switch.
The surge protector is blown.
I'd check to see if it is the breakers. Those SQ d breakers don't like a fault on the line side of the neutral. I have seen it before.

 

[mbrooke]

There must be some unique problem with the generator. There are thousands of homes using generators especially during blackouts and they are all working OK , right?

Not necessarily a problem. Different makes and models of gennies have different wave-forms. I've been on here long enough to know threads where the AFCIs were tripping on the generator without problems in the wiring or a defect within the AFCI itself.

However your point is valid, see my reply below.

For starters the Customer had just back fed the panel without a transfer switch.
The surge protector is blown.
I'd check to see if it is the breakers. Those SQ d breakers don't like a fault on the line side of the neutral. I have seen it before.

Honestly, I may have spoken to soon in prior post. :ashamed1: Damage from an over voltage could have damaged the AFCIs where the will now sporadically trip regardless. Interesting to know how they behave when the power comes back.

 

[ptonsparky]

There must be some unique problem with the generator. There are thousands of homes using generators especially during blackouts and they are all working OK , right?

Yes, but when you add AFCIs, it opens a whole new can of worms.

 

[mbrooke]

Quick possibility is that there is a ground to neutral bond at the generator.
That means that any circuit protected by an AFCI breaker that includes ground fault (GF) detection might false trip even though a logical analysis will indicate that all of the neutral current for the circuit must still return through the neutral connected to the breaker.
Other possibility is that the generator is producing a waveform that mimics a series fault signature and the breakers trip whenever the load on their circuit goes above 7-8 amps.

This might require a separate thread, but I am having trouble understanding how GFP can trip without a fault on the line side. N/G on the load side should not make a difference from my understanding.

Power grid may be out, and main breakers off, but main-bonding still connects everyone's secondary system noise thru service neutrals.

Stand-alone generators, correctly installed or not, with possible leakage currents or noise, can propagate thru utility neutrals to trip your A/GFCI breakers.

Try lifting utility-side neutral ahead of back-fed breakers, but perhaps not ahead of main-bonding where electrodes get disconnected.
If lighting strikes are probable, opening your path to the grounding electrodes is not a good idea.

You still have TELCO wires coming in which are bonded to the MGN at the pole and bonded to the service at the house. Aka second noodle.

 

[qcroanoke]

Yes, but when you add AFCIs, it opens a whole new can of worms.

True, but this is the first I've heard of it on here. Seems we should have heard of problems by now.
GFI on the generator tripping Yeah, But not AFCI's in the panel tripping.

 

[brantmacga]

Power was restored today; customer called and said all the breakers are still tripping. Sounds like they got fried. The surge breaker is also out, and I was told two TV's let the smoke out. They're all on P&S TVSS receps also. I think they got a pretty bad surge.


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[qcroanoke]

Power was restored today; customer called and said all the breakers are still tripping. Sounds like they got fried. The surge breaker is also out, and I was told two TV's let the smoke out. They're all on P&S TVSS receps also. I think they got a pretty bad surge.


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Well, that's too bad. Lots of money in breakers alone. Probably just the beginning for them.
Maybe a 7200 line falling across their house drop.