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When I opened up my walls for a kitchen remodel I discovered what I'm pretty sure is a multi-wire branch circuit. It has a 12/3 (black + red + white + ground) NM cable going back to the breaker. I think the black wire is attached to breaker 6 (20-amp) and the red to breaker 8 (20-amp) which are both on the same side of the panel stacked one on top of the other. From reading about this it sounds like the white neutral wire is shared for both circuits. I also read that unless this is wired correctly to a double pole breaker so that the current in each circuit is on different phase there could be a fire hazard on the shared neutral.

What are some simple tests I can do to make sure this is wired safely and correctly? The house was built in 1986 so it has been this way all this time and I assume is wired safely and correctly but I want to make sure before closing everything back up. It sounds like the key to this is that the two circuits are on a double pole breaker and each one is wired to a separate pole.

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  • Those two breakers should be ganged together. On many models of breaker you can add ganging by running a stiff wire (#12 or #10 copper works fine) through holes in the switch handles. Then bend the ends of the wire to hold them in place. Or you can replace them with a ganged breaker.
    – wallyk
    Aug 2, 2014 at 21:52
  • When you say ganged do you mean that when one flips to the "off" position it should pull the other one with it? They are not currently that way.
    – Shane Wealti
    Aug 2, 2014 at 22:26
  • Yes indeed, I mean mechanically ganged so that if either is shut off, the wires are dead. This is a basic safety precaution for anyone working on the wires. It also protects dual 120/240 volt appliances from unexpected conditions.
    – wallyk
    Aug 2, 2014 at 23:59

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Use a multimeter to measure voltage between the two hots (black to red). You should get somewhere around 240 volts. If you get 0 volts, the breakers are on the same leg.

An empty service panel looks like this

Empty Service Panel

I've drawn rectangles where breakers would go, and labeled the legs A and B. As you can see, breakers across from each other (left/right) are on the same leg, while breakers next to each other (up/down) are on different legs.

If you measured between breaker 1 and 2, you'd get 0 Volts. This is because they're on the same leg, so they're at the same potential. If you measured between 1 and 3, you'd get ~240 Volts. These breakers are on separate legs, so they're not at the same potential.

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  • Thank you for the photo and diagram explanation. This was very helpful.
    – Shane Wealti
    Aug 8, 2014 at 12:39
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With most panels circuit#6 and8 will be separate phases in the panel a 2 pole breaker will not fit in the panel any other way but a tandem breaker will. You can verify the phasing by using a volt meter between the red and black wires on the breaker needs to read 240volts .if it reads 0 it is wrong.

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Don't use wire. Either replace the two breakers with a two pole breaker or purchase a handle designed for the purpose. The NEC uses the word "approved" when discussing ganging the two breakers. Electricians have been using wire and machine screws for years, but they are not legal.

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  • NEC 240.15 (B)(1)
    – user24125
    Aug 9, 2014 at 1:17

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