A few years ago a contractor added two 20 amp lines from the breaker box to a knee wall on the second floor where they terminated in a junction box. They were put there for future use in a central AC system.

We did add central air eventually but those 20 amp lines weren't used (so I thought). I was going to connect to one of those lines the other day so I could add an outlet to a wall without any, and noticed that inside the junction box those 2 lines were connected and powering a 12 awg wire which I haven't traced yet.

Is it safe to have those 2 separate 20 amp lines, each on separate single pole breakers, connected to each other? Does that connection create 240v but still at 20 amps?

Here's a photo of the junction box:

enter image description here

  • Can you provide a photo of the wiring inside the box?
    – Tester101
    Commented Feb 24, 2017 at 14:27

2 Answers 2


It would never be legal to use two separate Romex cables as part of a single circuit. That is because conductors must be kept tight to each other so their magnetic fields cancel each other out. Without it, you induce eddy currents and heating into anything between, like the Romex staple. That would see 20 ampere-turns of EMF, and if that doesn't seem like anything, it only takes 8-10 ampere-turns to operate a reed switch.

If you needed plain 240V, you can use a single 12/2 and re-task the neutral to be the other hot. Mark it with tape or paint to show it's not a neutral.

Most 240V air conditioners do not need or want neutral.

In your photo, it appears the lower left Romex is disconnected. The neutral is stripped and ends in the upper right corner of the box, and the hot has a white wire-nut taped onto it (which is good practice as wire-nuts don't like to hold onto a single wire). The ground splice has the right number of wires on it. The work looks fine, though I'd have capped the neutral. Neutral is not ground.


Depending on how it's connected, and how the breakers are oriented in the panel. Yes, it could provide a 240V 20A circuit.

If this is how it's being used, then the breakers should have their handles tied together.

  • Oh jeez. I took a better look and it turns out the 2 lines are not tied together at all. One of the 20 amp lines is capped off and not connected to anything. Thanks for your input however.
    – user66761
    Commented Feb 24, 2017 at 15:34
  • 1
    If the two lines were on separate legs of the service, and they were connected to each other, that would be a 240V short-circuit. If they were on the same leg of the service, and were connected together, you'd have conductors in parallel (which is a code violation).
    – Tester101
    Commented Feb 24, 2017 at 15:37
  • By "separate legs" do you mean each line having its own neutral, as opposed to using a 3 wire with 2 hots and a shared neutral?
    – user66761
    Commented Feb 24, 2017 at 16:02

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