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I recently moved into a new apartment with... "curious" wiring. There is a single 15 amp/110 volt outlet that is directly wired to a 30 amp / 240v breaker. I suspect there used to be a drier and when it was removed the landlord changed the plug without changing the breaker/voltage.

My question is: is there a good way to replace the 30A 240V breaker with, say, a 15A 110V breaker and a blank so I can use the outlet as one normally would? If not, is there another way to downconvert the voltage so I can plug 110v appliances into the outlet?

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    In the US it is illegal for a renter to do electrical work. It's also illegal for the landlord to do the electrical work, which is how you ended up with this mess! Call in the landlord and ask that it get fixed. Depending on how much you like the place and the landlord, you may have to call the city inspector to get it fixed.
    – FreeMan
    Aug 18, 2021 at 16:34
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    What is the voltage between hot and neutral? You are allowed to measure that.
    – Harper - Reinstate Ukraine
    Aug 18, 2021 at 17:06
  • What is the actual risk to this tenant in using this as is for ordinary 120 V appliances? Should he switch off the breaker and not use it until it is brought to code? Suppose he tests it with a plug-in circuit tester and it tests OK. Would that tell him it has separate ground and neutral back to the panel?
    – Jim Stewart
    Aug 18, 2021 at 17:26
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    If one had an outlet with a 4-pin 230V connector, would there be any sort of box one could plug in which would contain two 20A double-pole breakers and two double 120V outlets? If the outlet is fed by four wires, I would think such an arrangement might be more useful than having a single 120V 15A outlet.
    – supercat
    Aug 19, 2021 at 14:55

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Well, first, you can't do work in a rental property without 2 things.

  • Landlord's permission to do the work AND
  • Local government permission to do the work, which will only happen if the work is a) trivial or b) done by a licensed electrician.

That's the law.

"But this is such a minor thing. Why all the fuss?"

Oh, nothing minor about this! Dryer wiring, especially in older homes, often does not have a ground wire - it is wired hot-hot-neutral. It's not impossible to put 120V receptacles on that, but they need to be GFCI if they do. Sometimes it uses SE cable which has a bare neutral. Further, some older dryer wiring is actually wrong and can't be used for 240V, but can be used for 120V.

Dryer wiring in general is a hot mess, hard to keep Code legal, and really does not lend itself to tinkering by amateurs.

And we know the amateur brigade was here because of the mismatched breaker and receptacle. 20A breakers can feed 15A receptacles, but 30A breakers cannot.

...Maybe if the receptacle wiring is perfect.

But, if everything inside the receptacle was "tip top" -- 4-wire dryer feed (or metal conduit carrying the ground instead of a wire), one hot wire capped, neutral on neutral terminal and hot on hot terminal...

Then, I think you could limbo under the "trivial" category IF you do one super simple thing: Swap the 30A/240V breaker for a 20A/240V breaker. (15A sockets are allowed on 20A breakers if there is more than one socket on the circuit; almost any dual receptacle will do.)

That way you avoid complications with dangling wires in the panel, and getting the right blank cover plate (which is itself a real bug-hunt). The extra pole barely costs more than the blank cover plate, and is sturdier and easier to find.

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    "Sometimes it uses SE cable" - I didn't know we made cable!
    – Vikki
    Aug 18, 2021 at 23:55
  • You might change "Dryer wiring, especially in older homes, does not have a ground wire" to say "sometimes in older homes"The NEMA-14 30R outlet into which my electric dryer is plugged in my 100 year old home is properly grounded. There is an old, three-wire outlet for a dryer down in the basement, but that had been disconnected by some previous owner before I bought the house twenty years ago.
    – Solomon Slow
    Aug 19, 2021 at 17:36
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I would comment, but can't yet.

Per: "What is the voltage between hot and neutral? You are allowed to measure that. – Harper - Reinstate Monica"

I am guessing that you will find that when you do this, the charges will be 120, not 240. If so, someone probably figured they could easily solve the problem by just using 1 of the 2 hot lines. While this may work, it is not good.

My recommendation - bring this to the attention of the landlord and request that they have it corrected so that it meets current electrical requirements. If they hesitate on doing so, ask them to inquire with their insurance provider what coverage they have if a fire tied to a code violation circuit. Once I made that last suggestion, the problem in an apartment I rented was fixed the next day (after no action for a week+).

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Is it possible? Yes. But there are requirements to be met. Unfortunately, as a tenant you shouldn't make changes to the electrical system in an apartment and the landlord shouldn't either (unless one of you happens to also be an electrician).

At minimum, successful and code-compliant conversion would require the following:

  • One of the wires would have to be insulated in white or gray color and be used for the neutral
  • One of the wires would have to be insulated in green color or bare and used for the ground
  • One of the wires would have to be insulated in a "hot" color, typically black but possibly any color except white/gray/green and used for the 120 volt line connection
  • The wire gauge used for a 30A circuit is likely too heavy to be connected directly to the terminals on a 120V receptacle. It would have to be adapted down with "pig tails" to a gauge compatible with the receptacle.
  • The circuit breaker would be changed to 15A or 20A (20A if the chosen receptacle is a 20A device and the pigtails are 12 gauge; 15A otherwise because this is a single-receptacle circuit.. unless the junction box has room for two 15A receptacle devices).
  • Appropriate cover plate(s) on the junction box, an unused breaker or a cover plate so there's no open hole left in the circuit breaker panel's dead front, etc.
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    Seeing neither seems likely to be licensed electricians, by the question, think the word 'shouldn't' should be be changed to 'not allowed'(picky I know). Also sounds like this setup in the question, would fail any electrical inspection, plus having any insurance claims denied.
    – crip659
    Aug 18, 2021 at 15:34
  • If CO/ALR receptacles are rated for direct connection with #10 copper wire¹, then could a duplex one of these be placed here and wired as either a single wire or a multi-wire branch circuit? Of course, changingbto a 20 A breaker,, and if the latter with a change to a 20 A 2-pole breaker. ¹I assume CO/ALR receptacles are rated for #10 aluminum, so they should be mechanically capable of accepting #10 copper.
    – Jim Stewart
    Aug 18, 2021 at 18:12
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[ Note if this is a rental unit, in some places neither landlord nor tenant may do this kind of work and the following is just theoretical. ]

The live side of the outlet (the one with the shorter hole and the brass screw) should be connected via one wire to one of the breaker's two lugs. Another wire should connect the other side of the outlet to the neutral bus in the panel. If that's how it's done the outlet is reasonably safe to use now. You can and should replace it with a one-pole 20A breaker ASAP. You have to buy one suitable for your panel. A label in the panel will tell you what kinds you can buy. You can buy a filler panel for the other breaker space or buy another breaker for future use.

If the neutral side of your outlet is connected to the other pole of the 240V breaker (ie the work was done at the outlet but the panel was left as-is), that's disastrous and you should turn off the breaker til it's fixed.

Assumptions: 1) the wire from the panel to this outlet is #10 that was suitable for a 30A circuit. You can use that with a 20A circuit. If it's #8 or bigger you may need to do a little extra work at both ends. 2) Grounds and other connections were correct before, so I'm not addressing everything here, only the conversion from 240 to 120.

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    Electrically this is correct. However, in the US (at least) it is illegal for a renter to do electrical work. It's also illegal for the landlord to do the electrical work, which is how the OP ended up with this mess!
    – FreeMan
    Aug 18, 2021 at 16:33
  • Thanks, added to answer.
    – jay613
    Aug 18, 2021 at 16:34
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Notwithstanding the "you're not an electrician so don't touch it" angle, the answer is yes, you can absolutely convert a 240 volt dryer circuit to a 120 volt receptacle circuit. If the wiring is red-black-white-green (hot-hot-neutral-ground), just cap the red wire on both ends, go black-white-green (hot-neutral-ground) to the receptacle, run the black wire to a 15 amp breaker in the panel box, leave the white and green (neutral and ground) where they are in the panel box, and install a blank (or a spare breaker) in the empty slot.

The wire is going to be #10 AWG if it was a 30 amp circuit. 15 amps only needs a #14 AWG, but you're allowed to use thicker wire.

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    Bear in mind that a lot of people aren't electricians yet do electrical work on their own houses every day. That's kinda what this forum is for - helping people do electrical (and other work) correctly and safely. For the most part "You're not a __, so hire a pro." could be the answer to every question here, but that's not really appropriate for a "Do It Yourself" forum, is it. (Of course, I realize that not all locales permit non-licensed people to do the work themselves, so that does apply in some cases.)
    – FreeMan
    Aug 20, 2021 at 16:19

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