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Using AFCI breakers on generator power

11K views 15 replies 9 participants last post by  sbrn33 
#1 ·
When we rough apartments we usually try to hot up the meter bank for a building with a generator so that we can test the circuits in an apartment after they drywall to make sure there's no shorts or damaged cables. This is the first job that I've done with panels full of arc fault breakers. When I hooked up the generator to one of the panels it held for a few minutes and then all the arc fault breakers started tripping like popcorn.

There was no issue with the voltage coming out of the generator it was steady but it got me thinking that maybe the generator power wasn't good for the arc fault breakers but now my question is how can I test the wiring before they mud tape and paint the whole building?
 
#5 ·
Yep ... That or what crazy mofo said, and test with regular breakers.

I've seen crap chinese gens trip AFCIs , I guess the distorted waveform is seen by them and they don't like it.
 
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#4 ·
If the voltage regulator on the gen is the capacitor type (it usually is on small units), then the gen produces a distorted waveform, not a sine wave. If the gen was the inverter type, the waveform is even worse.

I don't know enough about AFCIs to know how they would be affected by a non-sine wave but I wouldn't be surprised if they can't handle it.
 
#8 ·
Not sure what your circumstances are, but we had a sub-panel once with arc fault breakers. All of them starting tripping. The cause was arcing on the breaker feeding this sub-panel.

Maybe there's some arcing happening upstream and the arc fault can see/feel it? It would be something beyond your control though.

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#12 ·
Lots of new homes have back up generators that don't trip the arc fault breakers and the fact the breakers didn't trip till they had been on for a few minutes seems odd.

Personally i would have taken one breaker from the panel and wired it to the generator as a quick and dirty test then run a drill/coffee pot as a load to see what happens.

If you look at a quality generator on a scope the wave isnt as smooth as grid power so that may affect the afci
 
#13 ·
I've had this happen with a couple of my customers homes and not been able to duplicate it. It always works fine while I'm there of course. I don't know whether it happens before the outage, when the switch transfers or after. Never been able to see it in person or duplicate it.
 
#14 ·
I'm using a pretty nice generac generator. What do you all suggest to test and make sure cables are good. I like the changinging out to regular breakers but I make up panels as we go when roughing. These are plug on nuetral breakers so putting in normal breakers and then changing out to afci is a lot of work. do most of you guys hot test or do you guys just rough-in and then fixed issues after trim out?
 
#15 ·
Generac generators are not exactly high end. I'd either use a true sine wave inverter generator ($$$$$) or one of these wacker neuson rental generators (they've got pretty clean output).

There is the possibility that there's just something wrong with all your circuits...
 

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