I'm doing some work inside a wall that has some 12/2 NM cable running through where I need to put something. The cable doesn't have any additional slack for me to route it around the obstruction. I initially contemplated using a wire splice kit to add some slack, but am worried about the longevity of the device, so I want to do it right and splice it in a junction box.

However (and I'm sure this is common) I don't really want an ugly cover plate in the middle of the finished wall. Fortunately, there's an existing electrical box very close by that's used for a switched light on a different circuit.

My question is this: can I use the existing electrical box to splice cables that are on a different circuit? Or does each box have to only contain cables on the same circuit?

1 Answer 1


You can have multiple circuits in the same box so long as you do not overload the volume of the box with devices and wires.

See this answer by @Tester101 that discusses box volume.

  • Cool. The box has enough room in it according to that info. Thanks!
    – iLikeDirt
    Jun 25, 2014 at 16:04
  • I did a similar configuration in a previous house, though it was just a junction box and not a light switch. What I did, for safety and future maintenance by future homeowners is wrote in magic marker on the cover plate of the junction box that it was being fed by more than one circuit. Not fool-proof by any means, but at least hopefully helpful for someone in the future.
    – Milwrdfan
    Oct 30, 2018 at 20:03

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