Recently started digging around further in my new basement. Found the air conditioner is wired as follows:::
10/3 wire coming from panel that is connected to a double 15A breaker (red to 1, black to the other, white is simply not connected, ground to ground block). – in a j-box 15’ down the ceiling the 10/3 connects to a 12/2 (black-black red-white ground-ground). From the j-box the 12/2 runs outside to the air conditioner another 20’ down the wall.
Don’t know when this was installed. Based on the wire dating it can’t be pre-2005. I didn’t wire this but want to fix it if this is not correct. House hasn’t burned down yet, obviously, but this just seems odd.
My thought is pull the 10/3 out of the equation and change it all to 12/2. What does the breaker need to be? Thank you!
Electrical – 10/3 down to 12/2 for Air Conditioner
electrical
Related Solutions
I think you've got the LINE and LOAD swapped. I think the red wire from the switch, should go to the single black wire that was on the old switch. I'd guess that the bundle of black wires is made up of the feeder, a feed to another branch, and the pigtail to the switch.
Figured out the wiring!
Huge thanks to @A.I.Breveleri and @Shalvenay for guiding me through this - I couldn't have done it without their help.
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Best Answer
You're always allowed to upsize wire
I don't know how your house came to have legacy air conditioning wiring that large, yes I do. Air conditioners have gotten more efficient and past owners may have retrofitted insulation.
But regardless, if the requirement is for 14 AWG wire, you are always allowed to use the larger #12 or still larger #10.
There is also nothing wrong with an unused white wire "coming along for the ride".
However, when a white wire is used as a hot in a 240V cable, you are required to mark the white wire with tape. I strongly prefer wrapping the tape around the wire; flags can easily be torn off, especially as they age.
As far as breakers, if your panel is Eaton, Cutler-Hammer, BRyant, Challenger, or Westinghouse, Eaton breakers are almost certainly correct. If it's anything else, it's probably a hazardous mismatch, but anything is possible with Eaton; we'd need the panel brand and model, and the lettering on the breaker to be sure.