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How should I safely identify which breaker controls which fixtures & receptacles in a Multi-Wire Branch Circuit? There is intentionally a handle tie for the MWBC in my panel which must be kept to ensure no one electrocutes themselves working on the individual circuits in the future.

Is it safe to temporarily remove the handle tie in order to turn off 1 of the breakers at a time to identify what fixtures/receptacles are on each branch (of course putting the handle tie back afterwards), or is there a safer/better way?

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    In most cases, under normal workmanship practices, the color of the hot wire will tell you.
    – Ecnerwal
    Jun 25, 2021 at 18:55

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This can be done without removing any coverplates:

Identify all the receptacles on both legs of the MWBC by turning off the paired breakers and testing receptacles with a 3-prong tester, or a non-contact voltage tester, or a lamp, or a VOM. You could mark all these receptacles which were disconnected by switching off the breakers with a sticker, post-it note or piece of tape as you go.

Then switch the breakers back on. Plug an extension cord into one receptacle of a duplex and put a sticker beside that receptacle. Measure the voltage between this hot and other hots. Put a sticker beside each receptacle which measures zero (or close to zero) relative to that marked hot.

All hots on the same leg will have zero voltage. All hots on the other leg will have 240 V.

If your extension cord, as originally positioned, is not long enough to reach a receptacle, then unplug it from the original receptacle and plug it into any other receptacle which has already been tested and has a sticker beside it.

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  • If the op has a volt meter this could be quick I just pull the hot as some times it is a dpst breaker, but I do silly things like put the breaker numbers on my receptacles and switches.
    – Ed Beal
    Jun 25, 2021 at 20:09
  • Thanks for suggestion and helpful comments! I do have a volt meter and this is definitely the easiest and safest way. It took me a bit to understand the 240V but I understand now. The hots on different legs have the same electrical potentials, respectively, as the two hots coming into the electrical panel from the grid. The difference in electrical potentials, i.e. Voltage between them, is 240V as we know. So anything that is using the same "hot" in a circuit will have 0V across the volt meter, and anything using different hots will have 240V across the volt meter.
    – Aaron
    Jul 3, 2021 at 15:54
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There are two different wiring methods in use in the US: Conduit and cable.

Conduit is a metal or plastic enclosure holding individual wires (OK, it could have cable, but then just treat it as cable for this discussion). If you use conduit, then the two hot wires of a 240V or 120V/240V (like an MWBC) can be the same color. In fact, using the same color can save a bit because you can just use three colors (black for hot, white for neutral, green for ground (and no ground with the right type of metal conduit)) for just about everything. So if you have conduit and the wires are the same color then you need to actually figure out which wire is which.

Cable always comes the same way: 2-wire = Black & White. 3-wire = Black & Red & White. For an MWBC, of course, you would use 3-wire cable. With a 3-wire cable, there is no ambiguity. Properly wired, black and red will continue through the system until you have a split, at which point you can switch to 2-wire cable.

Open up your receptacle boxes. If you see black & red & white, then unless there is some really poor wiring (i.e., black & red swap at some point), they should match all the way back to the breaker. If you see just black & white then you trace back until you find where this split off from the MWBC to figure out whether the black goes to the black wire or the red wire back to the breaker.

The only problem is if you have conduit and the two hot wires to the breaker are the same color. In that case, shut off the double-breaker and remove/cap one of the hot wires and then turn the breaker back on, and you should be able to figure out easily enough which receptacles are connected to each hot wire.

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