For example, I have a 12/3 cable in which the red and black wires are controlled via separate breakers. The 12/3 drops into a single-gang outlet, out of which runs a 12/2 to another room. Is there a word/term for this (joined circuit, sistered circuit)?

I'm looking for a polite term ;)

(EDIT: Changed /4, /3 to /3, 2 - all cables mentioned contain grounds)

  • 2
    When you say "12/4 cable" and "12/3" do you mean 12/3 with ground, and 12/2 with ground?
    – Tester101
    Commented Nov 7, 2011 at 19:51
  • @Tester101 - Yes, exactly. Commented Nov 7, 2011 at 20:12
  • It's an understandable confusion. With cordage (flexible cords), the ground is insulated green and does count as one of the numbers. So a refrigerator circuit goes from 14/2 in the wall to the socket, then 14/3 cordage to the fridge. An RV goes from 6/3 in the wall to 6/4 cordage. Commented Dec 5, 2020 at 20:06

2 Answers 2


enter image description here

From Wikipedia

Split phase shared neutral (North American Wiring)

In split phase house wiring, for example, a duplex receptacle in a kitchen is typically connected with a cable that has three conductors, in addition to ground. The three conductors are usually colored red, black, and white. The white serves as a common neutral, while the red and black each feed, separately, the top and bottom hot sides of the receptacle. Typically such receptacles are supplied from a ganged breaker, i.e. a breaker in which the handles are tied together for a common trip, so that if one kitchen appliance malfunctions and pops the breaker, the other side of the duplex receptacle will be shut off as well. This is called a multiwire circuit.


These types of circuits must use a double pole circuit breaker

enter image description here

While the NEC recognizes this configuration, there is open debate as to weather or not this is a safe practice. For more information see Understanding the Dangers of Multiwire Branch Circuits


Multiwire circuits for 3 and 4-way switches

Switch legs, also called travelers must now be in a different color to be easily identified. A few years ago the white wire could be used as a traveler but code changed that to lessen the confusion of identifying the traveler. Now instead of running a piece of 14/2W/GRD or 12/2W/GRD for 3-way you have to use 14/3W/GRD or 12/3W/GRD. Same goes for 4 Way's also.

  • This sounds like what I'm looking for, I think. A double pole breaker is not used however. This is original wiring (1967). I don't know whether this was acceptable then but hopefully the terms will make it easier to search. Thanks! Commented Nov 7, 2011 at 23:05
  • I've seen this used to go from a new breaker box, to where the fuse box used to be. Commented Nov 8, 2011 at 6:26
  • @overslacked this wiring technique goes back a long way, and was originally used to reduce the amount of wire needed (lowering installation cost).
    – Tester101
    Commented Nov 8, 2011 at 21:23
  • @lqlarry, that edit probably makes more sense as a comment.
    – BMitch
    Commented Nov 27, 2011 at 19:51

It sounds like a poor man's 220. Are the breakers next to each other vertically in the box? If so, then black is carrying 110 from one line, and red is carrying 110 from a second line.

Strictly speaking those lines should be fed into a single double throw breaker which covers two posts in the box.

  • 1
    It's not ever used as 220 - just two 110s that happen to be in the same sheath most of the way.... Commented Nov 7, 2011 at 23:00

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.