I'm reconfiguring my kitchen and moving some stuff around, which necessitates moving some outlets and switches. This is my first attempt at any kind of electrical work, so finding weird things makes me nervous.

It appears that my house (built in 1905 and remodeled several times before I bought it in 2004) used to have an electric oven. It now has a gas oven and a 110V 20 amp circuit that is supposed to power the electrical part of the oven (a clock and the ignition for the burners and oven) and a microwave/hood combo.

When I took off the oven faceplate, I found a 240V box behind it with big white and black multi-stranded wires (and a ground). It appears that someone used one strand of each of the big wires and attached that to the outlet's terminal screws. Then they used wire nuts and pigtails to run normal 12/2 (w/ ground) wire up to the microwave/hood.

How should I deal with the 240V cable that runs from the breaker box to the outlet? Do I need to pull it out and replace it? Is there a way to wire nut a 240V stranded wire to a 120V wire, and is that an okay thing to do? I realize that as long as the breaker is only 120V, the wire is just bigger than it needs to be, but I worry that someone might see the 240V wire at the breaker and try connecting a 240V circuit without checking for smaller gauge wire downstream. Best I can tell, the 240V cable runs in one piece from the breaker box all the way to the outlet.


picture of box box from another angle box with wire nuts and tape removed

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    Sorry, forgot about the weird rules of this site. This is a comment, not an answer: First off, you need to stop referring to things like "220v cable", "110v wire", and "220v box". There are NO such things. Can you post a pic of this box? It sounds suspect but I am not getting a complete idea from your description. – Speedy Petey Jul 29 '14 at 0:24
  • Sorry. As I said, this is my first attempt at electrical work on my house. I didn't expect to find wiring adequate for a 220V outlet! :-) And I just realized I should have taken off the wire nuts so you could see the wire under the insulation. I'll go do that, now. – Todd O'Bryan Jul 29 '14 at 1:07
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    The size of the wire has nothing to do with the voltage, it has everything to do with the current. – Brad Gilbert Jul 29 '14 at 15:01
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    Also the size of the box has nothing to do with the voltage, it has to do with wire fill. You could use a box big enough to use as a breaker box with only one 110V outlet if you wanted. – Brad Gilbert Jul 29 '14 at 15:58
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    The voltage rating of these cables has to do with the thickness of the insulation on the outside of the cable, not the thickness of the wire itself. Pretty much all of the cables used in the USA are rated to 600 V, so they can be used for both 120 and 240 V distribution. – Pigrew Jul 29 '14 at 16:36

It looks like the cable was indeed originally run for a 220V stove.

When the stove was replaced with a gas stove, rather than run a new cable they just used the existing cable. This is fine as long as both ends are properly terminated.

I don't like the way they terminated the outlet though. I think they should have used a 12 AWG pigtail. ( assuming it was a NEMA 5-15 or NEMA 5-20 outlet ) Other than that I might have done the same thing depending on the difficulty of running a new cable.

( NEMA 5-15 is the designation of a US 110V 15A outlet )

If it is easy enough, I would run a 12 AWG cable from the breaker box to another box near the first with a NEMA 5-15 or 5-20 outlet.
Then either put an appropriate outlet on the existing cable with a 40A double pole breaker (assuming it is 8 AWG wire); or just put a blank cover on it.
If you do just use a blank cover, you should either ground out all of the conductors or remove the cable from the breaker box.
This way it can be left wired for both gas and electric stoves.

If it is difficult to run a new wire, I would just do what they did; except use a pigtail to connect the outlet. Don't cut back part of the wire, use an appropriately sized wire nut.

  • Yes, and if it's easy enough to run a #12 cable, I'd also run a 6/3 Cu cable so you can fit a modern, safe 4-wire oven connection and accommodate a 50-60A range/oven. Wire is cheap, access is expensive. – Harper - Reinstate Monica Aug 30 '18 at 0:47

Having a 40 amp circuit (nominally 8 gauge copper wire or 6 gauge aluminum) extended with 12 gauge copper is worrisome. There are worse electrical faux pas possible in an old house, but the most expedient thing to do in this case is probably to replace the 40 amp ganged breaker with a 20 amp ganged breaker. That will provide proper wire protection from overheating and short circuits.

In theory that is simple, but in practice you'll probably have to use a short piece of 12 gauge into the new breakers and then wire nuts to join those to the heavier cable—unless you can find a breakers with large holes. That is okay inside the panel. That will also help signal future electricians that the wire is not 6 or 8 gauge all the way.

  • I think the ganged breaker has been replaced with a 20 amp non-ganged breaker. (Actually, there's a 20 amp breaker with a 20 amp on either side marked NC, but who knows if one of those is still attached to the multi-stranded white wire.) – Todd O'Bryan Jul 29 '14 at 1:22
  • I guess I should have an electrician deal with connecting to the breaker box. (I have one coming out to deal with another issue, so that's not a problem.) Should I also switch down to 12 gauge at the outlet end, using the same kind of wire nuts as in the box? (Actually, I guess that would make it easy to switch back to a 220V electric oven later...) – Todd O'Bryan Jul 29 '14 at 1:28
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    It appears to be a two wire cable (plus ground). If the OP wants a 120V circuit, they won't want to use a double pole breaker. They'll want to replace the 40 or 50 ampere double pole breaker, with a 20 ampere single pole breaker. Then they'll connect the black wire to the breaker, and the white wire to the grounded "neutral" bus bar. This is of course if the breaker is listed to accept the size conductor being used. I think most 20 amp breakers accept up to #8, but you'd have to check the label. – Tester101 Jul 29 '14 at 10:47
  • @Tester101, thanks for the clarification. I guess that's what they must have done already, since it's on a 20 amp breaker and one strand of each wire was attached to the appropriate screw in an outlet fixture. How can I tell for sure what gauge wire it is? White and black are stranded, but ground is solid. Does that help at all? – Todd O'Bryan Jul 29 '14 at 11:16
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    @TOB you could use a [micrometer]( en.m.wikipedia.org/wiki/Micrometer) to measure them, or look for printing on the insulation which should list the size. – Tester101 Jul 29 '14 at 12:34

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