I just removed an old mini-split from my son's house (hadn't worked for years). it was a 220v Fujitsu and I am putting in a 12k MrCool unit (110v). I am planning on re-using the circuit breaker, which is a 20a, and the wiring from the box to the outside disconnect, which is 10g. I'm pretty sure the wire can be re-used as it seems silly to run new 12g wire from the box, but my question is this: from the disconnect to the mini-split - can I use 12g wire? ADDED INFO: After seeing some replies, I looked at a pic I have of the disconnect box (house is several miles away). Is it possible for 12g to have an orange jacket?

  • You will, of course, be moving the white wire to the neutral bar, and removing any "used as hot" marking if that was ever properly applied in the first place?
    – Ecnerwal
    Commented Jun 3, 2022 at 21:11
  • Yes, Already did that, sorry for not mentioning. And no, there was never a marker put there, and I admit to not making one, putting it there and then removing it, lol. Commented Jun 3, 2022 at 21:13
  • Please revise your post title to ask the question, not announce that you have one.
    – isherwood
    Commented Jun 3, 2022 at 21:21
  • I apologize, I can't seem to figure out how to change the title. Commented Jun 3, 2022 at 21:25

2 Answers 2


If you have cable (thus, a white conductor) you can just re-use the cable in place, with appropriate reconnection and removal of any hot marking on the white wire when you move it from the breaker to the neutral bar.

If you have conduit you'll have to pull a white or gray for neutral.

You'll only be using 1/2 of the existing breaker.

Since the breaker is 20A, 12 AWG is fine as the minimum wire size you can use.

  • Actually, the 10g wire is 10/2 with a ground. I an experienced carpenter but like to double and triple check myself when the electrical issues get fancier than a simple wiring gig. I didn't think feeding 12g off of the 10g in the disconnect was a problem - I know that the other way around would be. Commented Jun 3, 2022 at 21:19
  • The other way would also be fine with a 20A breaker, actually. 20A means the minimum size you can use is 12G - you can use a larger size anywhere in the circuit for any reason or no reason at all, you just can't use 14 or smaller anywhere on it.
    – Ecnerwal
    Commented Jun 3, 2022 at 21:31

12 gauge is the minimum allowed on a 20 amp circuit/breaker. You cannot have 14 gauge.

So using 12 gauge is okay, even if some of the circuit has 10 gauge.

I imagine the old circuit had 10/3 cable,two hot and a neutral(white) plus ground.

With 120 volt circuit you only need one hot and one neutral(must be white or grey) wire plus ground.

The extra hot wire of the old circuit will need to be capped off(wire nut) at both ends.

  • 2
    All the 240V mini-splits I've met don't need a neutral, so I imagine you imagine wrongly.
    – Ecnerwal
    Commented Jun 3, 2022 at 21:17
  • Much less chance of making a mistake if a 10/2, just move white to neutral and you don't leave a live hot hanging around to bite you.
    – crip659
    Commented Jun 3, 2022 at 21:22
  • I assumed it was a 240v mini-split in there before, as the white and black wires were both hooked to the breaker. There is no extra wire hanging around. Commented Jun 3, 2022 at 21:26
  • @JimmiSalvatore That is the common 240 volt circuit for things that do not require neutral, to use the white wire for a second hot. Makes life easy to change to 120 volt, just move the white to the neutral bus in the panel.
    – crip659
    Commented Jun 3, 2022 at 21:32
  • Ed says that some 240V mini-splits have 120V head units e.g. ones with multiple heads, so need /3+gnd brought to them. Commented Jun 4, 2022 at 1:05

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