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Transfer switch trips one circuit whenever I get power back

Posted by bigyellow (My Page) on
Thu, Nov 8, 12 at 15:50

Last year I installed this 10 circuit transfer switch and I power it with my Ridgid 6800 Watt generator. I live in Westchester county in New York and between Hurricane Sandy and this early November snow fall (that has us once again without power), my generator is getting a nice little workout!

Now, for my problem. And as I'm typing this, it just happened! I got my power back (again!) as i'm typing this. Sure enough, one of my breakers tripped when I got my power back. This is a square D breaker with the test button on it. I was told that for code requirements, bedrooms now need them. I'm not sure why or what they do, but here we are. So here's what I notice:

1. When my transfer switch is set to "gen", my generator is on and I have no power, everything is fine.
2. When my transfer switch is set to "line" and my generator isn't on and hooked up and I *do* have powe, everything is fine.
3. When my transfer switch is set to "gen" , my generator is on and all of a sudden, the power comes back, my breaker trips
4. Once scenario #3 happens, if I put my transfer switch for that line to "line", reset my breaker and put the transfer switch for that line to "gen", my breaker trips.

So again, when I have power and my transfer switch is set to "line", everything is good. When I don't have power and my transfer switch is set to "gen", everything is good. When I don't have power and my transfer switch is set to "gen" and I get the power back, that one breaker trips. Any idea why this could be?


Follow-Up Postings:

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RE: Transfer switch trips one circuit whenever I get power back

The breaker is a GFCI breaker (ground fault) or an AFCI (arc fault) breaker?


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RE: Transfer switch trips one circuit whenever I get power back

Hi, thanks for responding. Since it's for my bedroom, I'm guessing it's an arc fault breaker? Anyway, here's a pic of it. The one that's the culprit is labeled "G", although the one right above it is just like it. I'll try and educate myself and find out what an arc fault breaker is for.


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RE: Transfer switch trips one circuit whenever I get power back

Arc faults are touchy. I've tripped them plugging in a central vac power head.

I would guess that the transfer switch kicking in and out is enough to trip it, but I don't know much about arc faults.

Are there other arc faults that are powered when the generator's running? If so, but only one's tripping, maybe it's faulty...but if it doesn't trip wh

en the regular power's on, something else may be happening.

A lot of jobsite/portable generators produce "dirty" power, full of spikes etc, which is why they're not usually good for computers and other delicate devices. That may be part of the issue.


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RE: Transfer switch trips one circuit whenever I get power back

Unfortunately, I only have one circuit that's powered by the generator that has an arc fault breaker. And of course, all of the other circuits behave just fine. What are arc fault breakers for?


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RE: Transfer switch trips one circuit whenever I get power back

They detect arcs in the wiring and shut off the power. An arc can generate sufficient heat to cause a fire without enough current flowing to trip the normal overcurrent part of the breaker. They have been phased in to the code over the past five years or so. Originally, only bedroom outlets needed to be so protected, later code requires them on all living space (other than kitchens and bathrooms which require GFCI protection).

As pointed out, some of the early ones are a bit twitchy. I know that a lot of the nuisance trips went away with later mods of the GE AFCI's. I don't know about square D on this.

Frankly, mechanical transfer switches like you have, aren't really reliable ways to switch things under load.


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RE: Transfer switch trips one circuit whenever I get power back

While it's somewhat difficult to think up a scenario that would easily cause this, there's a couple things I would check.

First I'd make sure that somebody didn't do some creative wiring and tie the two neutrals from the that breaker, and the one above it (which appears you are not transferring) and ran a multiwire branch circuit.

The other would be to see if somebody tied a neutral from another branch circuit, to this circuit, in a junction box downstream somewhere. Lift the neutral off the breaker and measure between the neutral wire and ground with an ohm meter - should be open. If not it's tied to another neutral somewhere.

Also, are you using any type of home automation for controlling lights and outlets?


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RE: Transfer switch trips one circuit whenever I get power back

The switching back to line power is not synchronized to the line power from the POCO.

Tripping an arc fault is not all that surprising.

Weird things can happen at a hot-hot crossover.

Hot from a separate supply (your generator) to hot from he POCO (when it comes back on), especially under load.

A newer AFCI might be a little less sensitive.

It is one of the reasons for some time lag between disconnecting a generator and reconnecting to the POCO.

It needs to be long enough to look like a clean 'OFF' before going back to the POCO.

In very large installations it can take a few seconds of 'OFF' time (especially with larger or more sensitive loads).


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RE: Transfer switch trips one circuit whenever I get power back

That makes sense. Do the automated transfer switches allow for that delay time? Anything in the house that's really critical ought to be on an UPS in addition, to allow for a smoother changeover.


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RE: Transfer switch trips one circuit whenever I get power back

I wonder if the switch is momentarily connecting both the generator and the line at the same time. This would definitely cause an AFCI to trip, I think.


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RE: Transfer switch trips one circuit whenever I get power back

The OP provided a link to the transfer switch he is using. He is NOT using an automatic transfer switch or a manual whole house transfer switch. He is using a 10 circuit manual transfer switch that allows for switching individual branch circuits between "line" and "generator".

As he explained: "When my transfer switch is set to "gen" , my generator is on and all of a sudden, the power comes back, my breaker trips."

From the way I understand it, he is saying that no changes have been made on the transfer switch and one particular AFCI breaker in the panel trips simply because his power has been restored.

While I can certainly see an AFCI tripping during a change from generator to line, or the protection device being overly sensitive, there appears to be something else going on here. Since the hot is switched to the generator, it would make sense to begin troubleshooting by suspecting that the problem is occurring on the neutral side.


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RE: Transfer switch trips one circuit whenever I get power back

What does POCO mean? I'm guessing it essentially means electricity from my utility company? I did a google search, but everyone talking about it just talked about it and I couldn't find an explanation.

Maybe it was simply something obvious I did wrong. When I get home, I'll take off the panel and see if I did anything crazy for that one breaker. I'll report back with what I find. Thanks, guys.


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RE: Transfer switch trips one circuit whenever I get power back

Weedmeister's comment just made me think of another possibility - current leakage between the line and generator hots in the "G" transfer switch, or it's associate wiring.


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RE: Transfer switch trips one circuit whenever I get power back

yosemitebill, I'll definitely look at how the neutral is set up for this breaker. And yes, it's a manual transfer switch I have.

ronnatalie, you say transfer switches aren't reliable. Would you recommend a interlock setup instead? Why are manual transfer switches unreliable in your book?


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RE: Transfer switch trips one circuit whenever I get power back

Make sure the generator ground-neutral bond is REMOVED.

Most generators come bonded for free standing use with a ground electrode.

When powering a residential main panel the ground-neutral bond is IN THE PANEL and should not be duplicated in the generator.

While the generator supplies two hots and a neutral, is is getting ground from the panel.

NOT the other way around (generator grounding the panel).


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RE: Transfer switch trips one circuit whenever I get power back

And POCO is POwer COmpany.


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