240V Dryer Outlet to 120V Outlet
March 21, 2008 12:06 PM   Subscribe

Is there an adapter for a 240V dryer plug that will allow a standard 120V to operate off of it (while still allowing for the full 240Vs for the dryer)?

My wife and I are planning on buying a washer and dryer soon. We're leaning on separate units. The problem is that we only have a single 240V dryer plug. My understanding is that these are really two 120V at a different phase...meaning there may be a magical device that would allow a 120V plug off of it for a washer to run off of as well. Does such a beast exist or are we stuck with combo units?
posted by hylaride to Home & Garden (12 answers total) 1 user marked this as a favorite
Possible, yes - advisable, not really - definitely against electrical code. There's not a 120V outlet anywhere nearby that you could run an on-wall conduit from instead?
posted by jferg at 12:38 PM on March 21, 2008

Even if you could, I doubt you'd have enough amperage on the circuit to run both.

You'll have to either buy a combo unit or call in an electrician to install a 110 outlet in the laundry room.
posted by grumpy at 12:39 PM on March 21, 2008

I've got my washer and dryer on the same 15 amp breaker, and it will trip if I run them both at the same time.
posted by StickyCarpet at 1:22 PM on March 21, 2008

Just in terms of voltage, sure— you could get a stepup transformer to convert to 240V. Probably you could find an adapter intended to let people run UK devices in the US, for example.

But that wouldn't be much help because the whole reason that some appliances are wired for 240V is they need more power. Twenty amps at 240V delivers twice as much power as twenty amps at 120V (but uses the same amount of copper wire). IIRC the 240V circuits in my house are rated for 30A. So unless you have a power outlet wired for 60 amps at 120V (and I'm pretty sure you don't) you won't be able to run your dryer from it.

(For reference, typical household circuits in the US are 20A for outlets, or 15A for circuits that only have lights on them.)
posted by hattifattener at 1:32 PM on March 21, 2008

^ Right answer, wrong question.

P.S.: Count me in on the amperage concerns.

posted by eritain at 2:11 PM on March 21, 2008

I don't think such a device exists legally in the US. The code is written to prevent two things; shocks and fires.

The amperage considerations of using both units at the same time if someone tapped the 30A to add a 15A is the LEAST of your possible problems. It is possible to tap the 30A outlet the same way it's possible to shoot yourself in the head, don't do either. To tap the 30A 240V outlet and put a 15A 110V plug on the same feed is illegal because it could very easily cause a fire.

The 30A line is no doubt fed with a #10 (AWG if we're in the US) wire capable of 30 amps and backed by a two pole (double wide) 30 amp breaker.

If some retarded electrician illegally tapped the 30A 240V at the dryer plug location to add a 15A 110V, he would probably use #12 wire good for up to 20 amps and if a short happened, or the washing motor locked and and the amperage draw spiked more than 15-20 amps, the 30 amp breaker would not trip and the wire would heat up very quickly and the insulation/loose paper in the box/lint inside the washing machine (depending on the source of the short) could catch fire. Keep in mind it's possible the breaker might not trip even if it drew more than 30 amps because the breaker is two pole and the draw would be on only one of the poles (the 110V would use only one of the two poles.) It's supposed to trip regardless of which pole draws more than the rating but I've seen it not trip.

It's probably best if you get an estimate of the cost of properly running a dedicated 15A 110 line from the distribution panel to a washing machine versus the extra cost (including convenience, load capacity, space considerations) of a combo unit.

I know you aren't looking to cheap out, that you are only asking if there is a convenient device or work-around for your situation assuming they would be safe, but such a device could not be made safe (and a safe work-around, while possible, would probably cost more than just running a proper new line) but this isn't an area you want to cut corners.
posted by Kensational at 5:08 PM on March 21, 2008

Response by poster: Kensational:
You pretty much summed it up. If it was possible, I'd do it. The combo units are rated at 30 AMPS and they share the one plug. They're usually smaller, though.

Oh well...thanks for the info!
posted by hylaride at 6:53 PM on March 21, 2008

This is easily doable for a few hundred dollars you can live with using just one device at a time. You need
  1. Triple pole double throw switch box and switch,
  2. 15 amp breaker box and breaker,
  3. 15 amp outlet and box (preferably of the surface mount variety)
  4. a 4 11/16ths extension box
  5. a 4 11/16ths box
  6. a few bushings
  7. a bit of wire
I'd advise hiring an electrician, here's what he'd do with these pieces:
  1. turn off the power to the outlet.
  2. remove the dryer receptical from the box.
  3. install the extension box on the installed box.
  4. connect the TPDT switch box to the top of the extension box with a bushing.
  5. run wire from the existing box to the DPDT switch box and connect to the feed of the switch.
  6. connect the 15 amp breaker box and the 4 11/16ths box to either side of the TPDT switch box with bushings
  7. run wire from each side of the switch to the side boxes (one hot leg to the breaker, both to the 4 11/16ths box)
  8. install the dryer receptacle in the 4 11/16ths box
  9. install and run the wire to the breaker
  10. attach the 15A receptacle box to the side of the breaker box.
  11. run wire from the breaker to and install on the receptacle.
  12. install the respective cover plates.
I've done this often to allow running a A/C wall unit from electric heat. The caveat is you can one use one of the receptacles at a time.

Having said that it'll probably be easier and it will be cheaper to use a surface mount product like WireMold to tap into the 110V power most likely available at the ceiling light (there is often unswitched power run into the ceiling box).
posted by Mitheral at 9:30 AM on March 22, 2008

This is very common on stoves, of course, and there is no code problem there. The key being that a stove with an outlet has a built in fuse/breaker to protect the outlet at the appropriate current level (15A). Adding a standard plug without special fusing would be a fire hazard.

The problem I see (or, you know, don't see..) is that adding a fuse to the line is essentially adding a sub-panel. I don't know exactly what the code requirements are for that operation, but it must be possible.

Mitheral, what I don't understand about your answer.. Where do you get the neutral from on those 220V electric heater circuits (normally they only get the two lives and ground, like this problem here -- that site has many related, but not identical questions).
posted by Chuckles at 8:21 PM on March 23, 2008

Adding a sub-panel at the dryer outlet.

Reuse a 240V dryer circuit.

Mitheral is probably right about "2. 15 amp breaker box and breaker" instead of a sub panel though..
posted by Chuckles at 8:50 PM on March 23, 2008

Chuckles writes "Mitheral, what I don't understand about your answer.. Where do you get the neutral from on those 220V electric heater circuits"

Through the wall A/C units like you see in motels and hotels are usually pure 220V at 10-15 Amps. We'd buy an entire hotels worth when they replaced them, recondition them and sell them. So we didn't need to source a neutral leg for 110Vs.

And the specified 15A breaker box is technically a sub panel, it just happens to only have a single circuit. I didn't call it that so people's eyes wouldn't glaze over any more than they already were. The reason I recommended hireing an electrician is the breaker box has to be either bonded or not depending on the specifics of your house.
posted by Mitheral at 5:59 PM on March 25, 2008

posted by ZaneJ. at 8:19 PM on March 25, 2008

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