Electrical problem - 240v outlet only giving 120v

Hi there.

I finally decided to get an air conditioner for the main room of my apartment. There is a single circuit outlet next to the window with a 6-20R which accepts either 6-15P or 6-20P, so natually I assumed it is 240v/20A. So after the hassle of finding an affordable 240v air conditioner, waiting for delivery and then waiting for installation (since I’m not comfortable hanging 140 pounds out of a fifth floor window by myself), the installer plugs it in and only the fan works and that only on low. He declares it DOA and tells me to call the store to schedule a replacement install.

However, I get to thinking that perhaps I should have not assumed 240v. Out comes the multimeter, and sure enough I’m only getting 125v across the two hots. (125v from one hot to neutral, and 0 from the other hot to neutral.)

The building has incredibly old subpanels and there’s no double-pole breakers, however there are two breakers off by themselves. One of these breakers does handle the 125v I’m getting on that outlet - the other doesn’t handle anything currently; that is, turning it off doesn’t turn anything else off.

Next, I think that perhaps the wire was loose in the outlet, so I turned off both breakers and removed the outlet. There are only two wires to the outlet, black and white. This gets me thinking, as I didn’t think it possible to have only two wires provide 240v, I thought you needed at least 2 hots and a common neutral.

Anyway, I’m still trying to get in touch with the super, but I’d like some thoughts as to what the problem might be and how best to solve it. All I can come up with is… A) a problem with the breakers, or B) the previous tennents had no clue what they were doing and put a 6-20R on a 120v line.

A problem with the breakers would be ideal, because the building would have to fix it, and I’d be cool again. If this line is indeed only 120v, I don’t think rewiring is an option, so I’m stuck with an air conditioner I can’t use nor return, and (while I’d like to say it’s entirely the prinicple of the thing) is a good chunk of money I don’t want to throw away.


A 220 V. circuit doesn’t actually require three wires, two will do. However, in that case they wouldn’t be black and white. The white one would be marked with paint on the insulation. That shows anyone working on the circuit that the white one is “hot” and not a neutral.

Since only a black and a white wire come to the outlet, It appears that whoever wired the house didn’t hook up the other leg of the 220 V. source.

You could use the white one as the other leg of the 220 if you can identify which one of all those white wires it in the panel. That, however, might very well be contrary to the electrical code and the validity of your fire insurance could be in question if you wire something contrary to the electrical code.

I think you need and electrician.

It is possible to have 240V on just two wires, and it is commonly done for circuits not needing a neutral, such as electrical resistance heating. Appliances of the clothes dryer, kitchen range, and air conditioner variety do need the neutral to handle the 120V components, such as, in your case, fan motor, indicator lights (if any).

Don’t know enough about your situation to determine if rewiring is an option. Good luck.

Each hot should go to a pole on the breaker panel - this should by code be a 2 pole breaker but from a purely functional aspect, you would get the same results with two 1 pole breakers. The neutral should go to the neutral bar.

It sounds like the receptacle is wired as a 120V outlet.

As mentioned previously, you only need 2 wires for 240V. Three are commonly used to derive 120V from either hot to neutral.

You can get a clip that ties the two bats of one-pole breakers together so they both trip whenever one of them goes.

Is the plug on the ac 3 prong or 4 prong? a 3 prong 220 is two hots and a ground a 4 prong is two hots, a neutral and a ground. If it requires a neutral you are screwed because you don’t have enough wires there.

My guess what has happened is it is you have a three prong. Based on the fact the fan will run I’m guessing the white wire is tied into the neutral bar. In the panel. To test this, use an ohm meter, test the white to the ground(bare copper or green) in the outlet box. If you get a dead short I would expect it to be an easy fix in the panel, simply taking the white off the bar and putting it to the appropriate breaker.

Just reread the first post the op said he only has two wires in the outlet box. For your purposes treat the metal box as the ground.

You’re not getting 125v across the two hots - you’re getting 125v from one hot to neutral. You could turn this into a 240v outlet by moving the white wire to a breaker on the other leg. If you put black tape on both ends, it might even pass code.

The only problem with that is using the metal box and grounding conductor poses a safety risk, which is why the NEC prohibited that practice for new work several code cycles ago. Reading the OP’s comments about the age of the electrical distribution system in his building gives me concern about the metal device box and associated wiring affording a low impedance grounding path. If it doesn’t do so, then potential for injury exists.

It was likely within code when it was put in place. Short of running a new wire the op doesn’t have another option. It would be a good idea to confirm it does go to ground by ohm-ing it out against something known to be a ground.