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Joined: Feb 2009
Posts: 2
aces Offline OP
New Member
I just wired a 17kw generator and transferred approx 20 circuits for emerg back-up. The customer complained on 3 separate occasions that 3 separate circuit breakers tripped, with no unusual loads. All breakers were 15amp and one was a arc fault. I've installed many generators before, but have never had this problem. The generator was a Kohler and we were very careful about transferring all grounds and neutrals to the new ATS.

Here are the specifics:
Breaker 1: 15 amp fed the garage doors; as well as a family room and frig outlet in the garage. This circuit should have been wired independantly and is a code violation. Performed amp check and found normal readings. Also checked readings while compressor for frig was running and the amps drawn were well within the 80% acceptable range. Recommend a separate circ

Breaker 2: 15 amp kitchen lights. Nothing unusual had occurred when breaker tripped. I did find that the breaker was not fully snapped in, which I suspect caused it to trip. Performed amp check and found normal readings.

Breaker 3: 15 amp ARC fault fed the bedroom circuit, and an office. AMP checked recorded 3.5 amps and when customer turned on printer an additional 8 amps was drawn, which again is acceptable. Recommend to customer to install printer on a dedicated circuit.

OTHER troubleshooting performed: Tigheten all conductors, ungrounded, grounded and grounding. Also tightened main conductors. Other than connections I can't think of any other checks, any help/feedback would be greatly appreciated.

Joined: Jul 2004
Posts: 9,791
Likes: 14
First I am not sure a fridge in a garage is covered by 210.52(B)(1) ex2. That only refers to kitchens. I am not even sure I would recommend the modern fridge be on a dedicated circuit if it is not in the kitchen. My side by side only pulls a bit over 3a.

As for your tripping, I wonder if you have sags coming from the generator that cause slow starting of motor appliances.
Is the microwave on that "light" circuit? (which would be a violation)
What other PC equipment do you have in the bedroom? Again a sag might make switcher power supplies draw excess current.
Do you have a recorder?

Greg Fretwell
Joined: Jan 2005
Posts: 5,370
Likes: 1
Cat Servant
I am speculating that there are some neutrals shared with genny circuits. This could act like a 'floating neutral' and cause the tripping.

Joined: Mar 2005
Posts: 1,213
Were the circuits tripping while running on generator, or while on utility power, or both?

Is this a 3-pole or 4-pole ATS? If a 3-pole, did you disconnect the grounding jumper in the generator? If a 4-pole, did you double-check to make sure the grounding jumper is there? I wouldn't expect a double-bonded neutral to trip any circuit breakers, though, it's more of a safety issue. A floating neutral can certainly cause issues.

Joined: Feb 2009
Posts: 2
aces Offline OP
New Member
Dear Steve, Cat and afr:

Thanks for taking the time to respond. Here are some additional details:

All trips occurred on the utility side. ATS is a 3 pole and no i did not disconnect the bonding jumper. Although, i can't imagine this would cause tripping. All neutrals and grounds were transferred individually from the Main panel into the ATS. Although,I have to admit I don't really know what a floating neutral is. Could someone expound?

Joined: Aug 2007
Posts: 853
3 pole ATS, You should not touch the grounds.
Leave them be,That is your bond.

If by chance you Isolated them, Now you have no bond. Hence the 'floating' Neutral.

Joined: Mar 2005
Posts: 1,213
Have any trips occurred since you tightened the connections/how warm are the breakers when they pop? It could be overload, could be nuissance tripping from overheating, or it could be cable damage somewhere causing intermittant short circuits. Given that it's multiple circuits, I'd tend to think it's probably not cable damage- it might occur on 1 cable, but the chances of an intermittant fault like that on 3 seperate circuits is rather low.

leland, the bond in question would be at the generator. If he's using a 3-pole switch, the neutral should be left alone in the main panel but unbonded at the generator; often, it comes from the factory with the neutral bonded to the generator frame and has to be removed in the field if not required.

Joined: Nov 2007
Posts: 763
I believe that AFCI's tripping with some generator setups is a fairly common problem.
There was a post on another site a while back about how they will often trip at the moment transfer back to utility power takes place.
The diagnosis was that since the generator neutral is bonded at the generator frame and the utility side neutral is bonded at the service of the building, they became common at the transfer switch, creating the problem.
I think it was also noted that the same thing could occur with GFCI circuit breakers used in the panel for individual branch circuits. The tripping didn't occur with GFCI receptacles used down stream though, for obvious reasons.
As I recall, the suggested solution for this issue was to use a transfer switch that also switched and isolated the neutrals along with removing the neutral to frame bonding jumper at the generator, creating a true separately derived system.

I suppose if the garage door openers and refrigerator, etc... are protected by a single GFCI circuit breaker, changing to GFCI receptacles in the garage may at least solve that part of the problem anyway.

Joined: Jan 2006
Posts: 558
Are the breakers in question made by "Siemens" by chance?? I ask this as I had a similar incident happen to me today, and after reading the original post, I think the problem may be with the breaker(s) if they are of the same manufacturer.


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