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Discussion Starter · #1 ·
Moved into a new house and tracing and documenting the panel and breakers I see something that looks wrong.

Inside the panel I see a 12-3 NMb wire with the black conductor connected to one breaker and the red conductor connected to another breaker directly below it. The wire runs somewhere to a bedroom, one breaker controls the lights the other breaker controls the receptacles. They share the same neutral conductor. This is a MWBC correct?

This is a GE panel and some of the breakers are the half size skinny breakers. So the 12-3 is attached to circuits 8A and 8B, my understanding is that with MWBC you need to be on opposite legs, and on the panel circuits 2, 6, 10 are on opposite legs of circuits 4, 8, 12 right? So 8A and 8B would be on the same leg? I need to rearrange them so they are on something like 6B 8A or 8B 10A?

There is no handle tie either.
 

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This is a MWBC correct?
Correct
my understanding is that with MWBC you need to be on opposite legs,
That is correct.
So 8A and 8B would be on the same leg?
Correct
6B 8A or 8B 10A?
That won't work. The breakers need to be beside each other so the handles can be tied together so they go off together. You would need something like 7 and 8 or 8 and 9. If you want to use half size beakers then you need a quad breaker with the two inside and the two outside tied.
It will look something like this one.

 

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You sound like you know what you are doing, but still learning a little.

Do make sure that you are actually on the same leg and incorrect now....ie 8a and 8b.

Make sure that is the original panel marking, and not some hack or accidental miss-marking by someone with a majic marker.

You can test if unsure with your multimeter between the two breakers. IF 0 volts, you are on the same leg and incorrect, if 240V you are correct for a MWBC and you are mismarked on the panel.

Good to correct immediately, even if it has been working for awhile as you may be overloading your neutral depending on your usage.

I've seen alot of panels mismarked/mislabeled. Usually, seems to me, that if someone is installing a MWBC, they are usually competant enough to hook it up correctly. (Maybe someone came along and moved breakers around.

Good luck
 

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An alternative you might want to consider is see if you can rearrange your circuits so your MWBC falls on adjacent slots and use your half breakers for 'traditional' circuits.
 

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Discussion Starter · #5 ·
You sound like you know what you are doing, but still learning a little.

Do make sure that you are actually on the same leg and incorrect now....ie 8a and 8b.

Make sure that is the original panel marking, and not some hack or accidental miss-marking by someone with a majic marker.

You can test if unsure with your multimeter between the two breakers. IF 0 volts, you are on the same leg and incorrect, if 240V you are correct for a MWBC and you are mismarked on the panel.

Good to correct immediately, even if it has been working for awhile as you may be overloading your neutral depending on your usage.

I've seen alot of panels mismarked/mislabeled. Usually, seems to me, that if someone is installing a MWBC, they are usually competant enough to hook it up correctly. (Maybe someone came along and moved breakers around.

Good luck

It's not a mislabel, as there was no label on the panel to start with at all, which is why I am now going through this tedious process to label everything.


Yes I hear you, someone who knew to wire a MWBC is not likely to be ignorant about needing to put them on separate legs. It's a head scratcher. You may be right, it could be someone coming along later and moved the breakers around.
 

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Discussion Starter · #6 ·
That won't work. The breakers need to be beside each other so the handles can be tied together so they go off together. You would need something like 7 and 8 or 8 and 9. If you want to use half size beakers then you need a quad breaker with the two inside and the two outside tied.
It will look something like this one.


joed, thank you. However I am trying to understand why it won't work. This is what I have right now.





Just to make sure, I showed them in blue and white to indicate different legs of the service, and I also showed the breakers in different thicknesses as I have a mix of regular and skinny ones.


The current MWBC breakers are in 8A and 8B, clearly on the same leg as you have confirmed.


Why can't I swap the 8A and 10A skinny breakers, to have them result in opposite legs, and add handle ties?
 

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My mistake on the breaker number system. You are correct. But a single tandem won't install across 6b-8a. You would need the quad version.
 

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Discussion Starter · #8 ·
My mistake on the breaker number system. You are correct. But a single tandem won't install across 6b-8a. You would need the quad version.

The current 8A 8B are not tandem breakers, they are individual skinny breakers. If I keep them as individuals and move 8A to 10A, can I put something like this?





The reason I hesitate to go to a quad is because I have two sets of MWBC in the wrong place. Changing them both out into quads would require quite a bit of shuffling, relabels, and probably conductors that need extending.


Which begs the question why both sets of MWBC are incorrect with no handle ties, strange. May be the legs are not set up as I have expected. I will check with a voltmeter first to make sure.
 

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If that is made for those breakers and fits ...you can. (It's just hard to find handle ties made for different breakers most times.
 

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May be the legs are not set up as I have expected.
You need to check. Some panels go ABABAB down one side some go AABBAABB.
I will check with a voltmeter first to make sure.
Good plan. You should have 240 volts between the two breakers.
 

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Which begs the question why both sets of MWBC are incorrect with no handle ties, strange.
The most likely answer would be that your house was built/wired before it was a code requirement to install the handle ties. IIRC, it was 2008 NEC.
 

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Discussion Starter · #14 ·
You need to check. Some panels go ABABAB down one side some go AABBAABB.

Good plan. You should have 240 volts between the two breakers.

After my tests, breakers 8A and 8B have 0v between them.


Breakers 8B and 10A have 245v between them.


So it looks like I will be swapping 8A with 10A either switching the breakers or switching the hot conductors. Then I will add a handle tie.
 
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