Two breakers, one circuit

Recently, I was changing a light fixture on my back porch and discovered that I had to shut off two breakers to cut the power to the circuit. I take that to indicate that somewhere, somehow the two circuits have effectively been crossed together such that the circuit can draw power from either breaker.
I'd like to fix this... is there a simple way of determining where the two circuits are conjoined?
Thanks.
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drhender wrote:

I hope the two breakers are not side by side in the panel. That would mean you have 220 volts going out to that light with both on. Careful you don't burn the place down.
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On Mon, 27 Oct 2008 19:02:19 -0400, Claude Hopper

If these were intended to be 2 separate 110V circuits, that got joined accidentally, you would have a short circuit. Hope you don't have those non-trip breakers.
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drhender wrote:

It is not that uncommon to have to turn 2 or more breakers off in order to completely shut off the power inside a single switch box. This is especially true of 2 or 3+ gang switch boxes that say lead to the garage from the kitchen etc. If you are saying that it takes 2 breakers to shut off a single light then that is a crossover. The first place to look is in the switch box. If not that then I would map out your entire system by systematically turning the 2 breaker on and off. Then find all the outlets or lights or appliances that come on with both beakers. Then open each box one by one until you find the problem.
There are other possible situations that could cause this kind of behavior such as an open neutral. But you would notice other problems like brighter and/or dimmer than normal lights elsewhere.
Sometimes neutrals from 2 different circuits are connected together somewhere and when you go to disconnect things you get an arc/shock as you are disconnecting the neutrals at the fixture box even though the power is off on the circuit you are working on BTDT. In this case the circuits are not really joined but you should go and try to separate the neutrals if you can. Most likely this was done in a 2+ gang switch box fed by 2+ circuits.
An Edison type (shared neutral) circuit where a duplex outlet is fed by 2 circuits someone replaced an outlet and forgot to break the joining tabs between the upper and lower outlet. If this were the case however the circuit would have a second problem where the 2 circuits were improperly put on the same 'leg' in the panel.
Kevin
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This could also be two circuits that use a common neutral. That would happen if you ran 12/3 like in a kitchen where the top receptacle is on one circuit and the bottom on the other, but they both share the neutral. Code requires that the breakers be tied together so both must be shut down to avoid killing somebody who thinks they're working on a dead receptacle.
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Actually, Code doesn't require handle ties, unless there's a 240V device somewhere on the circuit. IMHO, it *should*, but it doesn't.
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wrote:

In the 2008 NFPA 70 article 210.4(B) now requires a simultaneous disconnect on multiwire branch circuits.
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many years to get around to it.
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It sounds not good to me. I think you better fix it now. Call an electrician is the best idea. Posted from the Free Home Improvement Forum at http://www.spicyhome.com
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After a bit of thought, I realized that there was a single switch box in the kitchen that contained lights from both circuits... one switch (a 3-way) controls the light in the foyer and the rest control kitchen lights. That seemed like a likely spot to start looking so I pulled it open. I discovered that all of the neutrals in the box were tied together, crossing the two circuits together. I pulled the incoming and outgoing neutrals for the foyer light out and tied them together separately and the problem is fixed.
Thanks to all for the advice.
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Thanks for posting the final outcome.
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On Oct 28, 9:24 am, snipped-for-privacy@invalid.com wrote:

What fire hazzard, here it was to code. I have the same thing to the garage and its not going to be fixed until underground wires to the garage fail because I would have to trench up a yard and sprinkler system. I was told its called a California Loop, what ever that is, it was common years ago here to a garage that needed more than 15a, just learn to lable breakers and live with it if its a similar 3 way set up.
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