How to convert 250V recepticle to 110/120?

How can I convert 250V recepticle to 110?
In my bathroom is a recepticle with 2 horizontal eyes and a D-shaped mouth. One of the eyes has a vertical T component as well. The unit is marked 20A 250V. It was likely installed with the bathroom addition maybe 20+ years ago, maybe for a heater, or an A/C.
Inside, there are two hot wires (old insulation) running to brass screws on either side (mouth level) of the recepticle and a black-insulated wire running to a green screw. The feed is flexible metal conduit. When I poke my $5 tester in the eyes it lights up two lights (240V).
At the main panel there are two 40A breakers on the same bus that go to the recepticle. They might have been hooked together at one time but now, in addition to controlling the recepticle they control various household lights and recepticles and the garage. When I open either one of the breakers the voltage meter drops to only one light (120v).
What needs to be done to covert this recepticle to a standard household current?
Thanks in advance
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You need to do much more than just change this circuit; but the method for changing is very simple. Presumably a black wire goes to one breaker and a white wire goes to the other breaker. If you move the white wire to the grounding buss, you have a 120v circuit. But of course the outlet is wrong and will have to be changed to a 120v/20a outlet. Make sure you get the polarity right. (The wire going to the ground should be green insulated or uninsulated, so it is prudent to make sure it goes to the grounding buss on the other end, and maybe put some green tape on it to identify it as a ground)
Now, your other problems are that you have various 15a or 20a circuits attached to 40a breakers. That is very unsafe, for an overload will burn the house down before the breaker trips. You have to replace the 40a breakers with ones more appropriate to their actual usage and wire size. To do that you will have to identify what circuits are on each breaker, and make sure that no wires are attached to breakers that are too large to be safe. You will probably find that you don't have enough breakers to do this (which is why there are 40a their now) and will have to find a way to increase your breaker count.
This is not complicated and if you feel up to it, proceed. But if you are uncertain (as you might be if you have to ask the original question) it is best to get an electrician in to be be sure it is done correctly.
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Strange to have a 230 volt outlet in a BATHROOM like that! Possibly illegal? All sounds rather dangerous. The minimum however would probably be to convert the outlet to, white neutral and black live from a single pole 115 volt breaker of 15 or 20 amp capacity. Use a GFI (Ground Fault) outlet. (Probably mandatory for bathroom use in most jurisdictions). The minimum size of wire to the refurbished outlet should be 14AWG (15 amps) or #12AWG for 20 amps. Any spare unused wires should cut back and/or insulated 'at both ends'. Do not leave them connected to anything. All rewiring should be done in a standard manner. The GFI outlet and the metal wall box MUST BE grounded and in some jurisdictions must also be bonded to anything metal within reach (two metres?) such as a metal washbasin, metal taps etc. In view of what sounds like a less than standard state of your wiring and circuit breaker box be careful cos there might be insurance implications especially if you change things yourself! Also some other electrician or homeowner or family member might later come along later and if it's non standard there might be an accident! As a side note don't ever use two single pole circuit breakers like that NOT LINKED together on a 230 volt circuit (North America). Better use double pole breaker. Again insurance companies definitely prefer that! Check the requirements in your jurisdiction; Fire depts. and insurance companies like that!
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When I dscribed the one-buss setup to the hardware salesman he suggested I cut one of the hot wires at the recepticle and use the 3rd wire for neutral. That would be simpler, but would it work?
If I can paraphrase your recommendation: at the box, take the white from its breaker and put it to the neutral, use the 3rd wire as a ground. Is there a good way to determine at the breaker which wire is that recepticle's white wire?

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That is idiotic. If that is your level of understanding, please get an electrician to fix your mess before it burns down.
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I thought I was paraphrasing your advice: "Presumably a black wire goes to one breaker and a white wire goes to the other breaker. If you move the white wire to the grounding buss, you have a 120v circuit. But of course the outlet is wrong and will have to be changed to a 120v/20a outlet." Of course that's why I did it, to double check. maybe you could try again. Thanks
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a
changed
again.
Changing a 240 volt outlet to a 120 volt outlet is usually cut and dried. Understand, based on the statements made in your original post, that your wiring has been hacked. You should not start swapping wires around until you know what's what. That means a trip into the attic or basement to see _exactly_ what the guy did. From what you described he probably tapped the 240 off of two existing 120 circuits, then discovered that the breakers wouldn't hold so threw in the 40 amp breakers. Plus you won't know for sure what the guy did the neutrals until you get up there and have a look see. Look in your breaker panel, if you see two separate cables coming into the panel with a black from each cable going to the two 40 amp breakers and the whites of each cable going to the neutral busbar, then the guy most likely combined two existing circuits and you need to find where he did it to see what else he butchered.
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puttster wrote:

To start with, it sounds like it was improperly wired to begin with. (using a white for one leg of a 220V line??? also to meet code the breakers must be coupled so they both go off at the same time) Who knows what else the hack that put that in may be on that circuit, so just going to the breaker box and dropping the feed to 110 could cause some serious problems elsewhere with something expecting 220V and it suddenly gets only 110. That could be dangerous.
I strongly suggest that you don't mess with that line until you know for sure exactly what is going on.
--
Joseph E. Meehan

26 + 6 = 1 It's Irish Math
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Of course the white wire should have had black tape on it to indicate it is a hot, but otherwise it is pretty normal. Or do you use 12/2 with two black conductors?
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is
black
It's true that 12/2 is commonly used for 240 volt circuits, however, in light of the fact that this circuit also feeds other 120 volt outlets, 40 amp breakers were used, and a black insulated wire was used to connect the equipment ground, an inspection by an experienced, qualified electrician is warranted. Usually when one finds hack wiring like that there's more butchered wiring elsewhere.
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with.
is
You would know wouldnt ya?
They call ya sparky for a reason dont they?
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