What to do with unnecessary red wire from 12/3 wire?


Old 08-10-15, 09:35 AM
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What to do with unnecessary red wire from 12/3 wire?

I am replacing a few receptacles in the kitchen and came across a weird wiring scenario.

There are two switches by the sink: one that controls the disposal and one that controls a light above the sink. They are on a separate circuits from the panel - the disposal on its own and the light on the dishwasher circuit. Both switches are single-pole switches, but the wire bringing power to the disposal switch is 12/3 (black/red/white/ground). All other wires in the box are 12/2. The black wire from the 12/3 is going to the disposal switch, but the red wire is wire-nutted to a DIFFERENT black wire coming into the box and then those are hooked up with a jumper to the switch controlling the light above the sink.

Though this scenario seems to be working fine, it doesn't seem right to me. It seems like the red wire is unnecessary in this situation, so my thought is to just cap it off with a wire nut and leave it in the junction box. Would that be the best thing to do, or should I just leave it as is?

Sorry if the explanation is confusing! Thanks in advance for the help
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Old 08-10-15, 09:56 AM
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Sounds like a multi wire circuit. Pull the front off the breaker box and see if one breaker has a black and one a red or if you have a multimeter measure between black and red. If you get 240 volts it is a multi wire circuit.
Old 08-10-15, 09:59 AM
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The red spliced to the black is just a continuation of the one circuit out to other parts of the circuit. Two circuits enter the box on the xx-3 cable, one leaves on the xx-2 cable. Quite common and perfectly fine.
Old 08-10-15, 12:08 PM
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This is not weird, but can be confusing. Rather than run 2 separate 12/2 cables into the box to supply power to 2 circuits, a single 12/3 was ran. This gives you 2 hot wires from the panel and the neutral is shared. Things to be careful with when working on a multi-wire circuit:

Ensure both breakers are off, black and red wires. In newer homes the breakers will be tied together. In older homes, you will have to hunt for the two.

Ensure the neutrals are pigtailed at that first box and only one neutral is attached to receptacle. Do not use the receptacle top and bottom screw terminals to continue neutral downstream.
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