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Old 02-18-2014, 10:00 PM   #16
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One breaker trips when I turn another breaker on


That's great that you're at least very well prepared. You'd love to see the questions we get just like yours and folks don't even own a simple tester.

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Old 02-18-2014, 10:01 PM   #17
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One breaker trips when I turn another breaker on


I'm the same way, it would bug me too. I was just suggesting an easy solution.
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Old 02-18-2014, 10:03 PM   #18
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One breaker trips when I turn another breaker on


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I'm the same way, it would bug me too. I was just suggesting an easy solution.
I definitely appreciate you verifying that this "okay" to do. I couldn't find a reason why it wouldn't be okay, but it's good to hear that it went through someone else's brain too.

Thanks for all the answers so far guys; I appreciate it. I suppose tomorrow I dig around a little more and see what I can find. Any more tips, feel free to keep chiming in.
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Old 02-18-2014, 10:10 PM   #19
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One breaker trips when I turn another breaker on


Here's a theory: there used to be two separate circuits, but at some point their hots got tied together in a box somewhere. But they're on different legs, so when both breakers are on, there's a dead short across the two legs. With either breaker on and the other one off, the circuit works. (Although it may be heavily loaded because it is, in effect, two circuits' worth of stuff.)

If I were going to try to diagnose this, I'd start by looking at all of the multi-gang boxes, looking for one that appears to have a feed that goes nowhere. Disconnect that feed, then switch the breakers (turn the first one off, then the second one on) and see if the "dead" feed suddenly becomes live.
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Old 02-18-2014, 10:13 PM   #20
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One breaker trips when I turn another breaker on


Have you positively identified the type of breakers used ?
Could be that they are "Arc Fault Circuit Interuptors" ?
In which case they are doing what they are supposed to !
When you close a breaker on a loaded circuit,
their will be some small arcing,
if its older and a little bit worn, maybe a bit more arcing.
If this is the case then it's normal.
I suggest you get the model number off the breakers,
and find out for sure if they are normal breakers or AFCI's ?
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Old 02-18-2014, 10:20 PM   #21
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One breaker trips when I turn another breaker on


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Originally Posted by fa_f3_20 View Post
Here's a theory: there used to be two separate circuits, but at some point their hots got tied together in a box somewhere. But they're on different legs, so when both breakers are on, there's a dead short across the two legs. With either breaker on and the other one off, the circuit works. (Although it may be heavily loaded because it is, in effect, two circuits' worth of stuff.)

If I were going to try to diagnose this, I'd start by looking at all of the multi-gang boxes, looking for one that appears to have a feed that goes nowhere. Disconnect that feed, then switch the breakers (turn the first one off, then the second one on) and see if the "dead" feed suddenly becomes live.
Thanks, I'll be trying this out tomorrow.

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Originally Posted by dmxtothemax View Post
Have you positively identified the type of breakers used ?
Could be that they are "Arc Fault Circuit Interuptors" ?
In which case they are doing what they are supposed to !
When you close a breaker on a loaded circuit,
their will be some small arcing,
if its older and a little bit worn, maybe a bit more arcing.
If this is the case then it's normal.
I suggest you get the model number off the breakers,
and find out for sure if they are normal breakers or AFCI's ?
Just plain 'ol 15 amp breakers, neither AFCI nor GFCI.
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Old 02-18-2014, 10:46 PM   #22
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One breaker trips when I turn another breaker on


Where are these two breakers physically located in the panel? Are they one on top of the other, or several spaces apart?

Am thinking MWBC.
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Old 02-18-2014, 10:50 PM   #23
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One breaker trips when I turn another breaker on


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Originally Posted by sirsparksalot
Where are these two breakers physically located in the panel? Are they one on top of the other, or several spaces apart? Am thinking MWBC.
They are obviously on opposite phases.
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Old 02-18-2014, 10:56 PM   #24
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One breaker trips when I turn another breaker on


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They are obviously on opposite phases.
hmm, still learning, so aren't MWBC on opposite phases?
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Old 02-18-2014, 11:37 PM   #25
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One breaker trips when I turn another breaker on


It could be a multiwire branch circuit that is shorting phase to phase. If the circuit was ran with 3 wire modern non metallic (romex) one of the breakers will have a red wire connected to it and one will have a black. Might check that real quick and let us know. Could make things a bit easier to isolate the problem.
I've come across this a few times in my career but it was always the result of a home owner remodel and homeowner DIY wiring.

Also what is your location USA or Canada ?
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Old 02-19-2014, 06:16 AM   #26
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One breaker trips when I turn another breaker on


Quote:
Originally Posted by sirsparksalot View Post
Where are these two breakers physically located in the panel? Are they one on top of the other, or several spaces apart?

Am thinking MWBC.
One is directly on the of the other.

Quote:
Originally Posted by Stubbie View Post
It could be a multiwire branch circuit that is shorting phase to phase. If the circuit was ran with 3 wire modern non metallic (romex) one of the breakers will have a red wire connected to it and one will have a black. Might check that real quick and let us know. Could make things a bit easier to isolate the problem.
I've come across this a few times in my career but it was always the result of a home owner remodel and homeowner DIY wiring.

Also what is your location USA or Canada ?
USA (Philadelphia).

I'll check in the panel for a MWBC in a little bit and get back with my results.
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Old 02-19-2014, 08:49 AM   #27
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One breaker trips when I turn another breaker on


Most common cause of this is a split wired receptacle that is replaced and the tab is not cut off. We need to know if there is a red wired involved. If there is then simply start opening receptacles on the circuit and look for a red and black on the same receptacle. If there is then the tab between the screws must be cut only on the hot side(gold screws).

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Old 02-19-2014, 09:18 AM   #28
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One breaker trips when I turn another breaker on


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Originally Posted by joed View Post
Most common cause of this is a split wired receptacle that is replaced and the tab is not cut off. We need to know if there is a red wired involved. If there is then simply start opening receptacles on the circuit and look for a red and black on the same receptacle. If there is then the tab between the screws must be cut only on the hot side(gold screws).

Awesome Joe, thanks. I will double check on this. And I will keep everyone posted on what I find
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Old 02-19-2014, 10:41 AM   #29
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One breaker trips when I turn another breaker on


Quote:
Originally Posted by joed View Post
Most common cause of this is a split wired receptacle that is replaced and the tab is not cut off. We need to know if there is a red wired involved. If there is then simply start opening receptacles on the circuit and look for a red and black on the same receptacle. If there is then the tab between the screws must be cut only on the hot side(gold screws).
I just checked in the panel. No MWBCs. The only two red wires were for two 240-volt circuits. I'm assuming that it's going to be a lot harder to diagnose where the wires are crossed since there is no red wire that would be giving it away in any of the boxes.

Any other tips? If not, here's what I think I'll do, and correct me if you have a simpler idea. I will disconnect the hots from every switch and receptacle. I will test each of those hots twice: once with breaker "A" on and "B" off, and again with breaker "B" on and "A" off. Each time, I will mark with tape where I had power coming in. Hopefully, then, I will be able to identify the box where there are two separate hots coming in.

Sound good? Or do you guys have any other better/simpler ideas?

Last edited by hellohello; 02-19-2014 at 10:44 AM.
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Old 02-19-2014, 12:11 PM   #30
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One breaker trips when I turn another breaker on


Not sure if it would help, but google "circuit breaker finder" (can't post links yet...) and you might be able to identify what breaker feeds what outlet. I used one to map my entire house out and found a few things mislabeled.

OR I like the simpler removing outlet covers to see where you might have a double fed outlet.

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