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Adapters exist for providing 120V from a 240V receptacle, such as for powering a gas range or dryer from the original electric range or dryer outlet:

240V to 120V adapter

Does anyone make a similar adapter that goes in the other direction?
Specifically it would plug into an existing 120V split kitchen receptacle and provide a 240V outlet for a European kitchen appliance. (It would be for resistance appliances only, so the 50Hz vs. 60Hz is not an issue.)

It would be easy to construct one, but the result would be potentially dangerous.
(Two separate 120V plugs means that when one is plugged in the other has a live exposed prong.)

What would be needed is a dual plug, such as this wall-tap has, but with only a single 240V outlet:

2-to-6 outlet 120V wall adapter

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    The upper and lower receptacles would need to be on opposing phases, so no. You'd have to draw from two different circuits and know their phase.
    – isherwood
    Mar 20 at 14:37
  • @isherwood, it is a split kitchen receptacle, with the upper and lower outlets 180° out of phase and attached to a double circuit breaker. Mar 20 at 14:39
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    Right, but how does the average user know that? It's a very low-success scenario.
    – isherwood
    Mar 20 at 14:41
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    The problem is combining the two hots into one which makes a big spark/short/possible fire. There is a hack to combine two 120v to make a 240v with two hots(a four prong plug). Europe uses a single hot.
    – crip659
    Mar 20 at 14:43
  • Does your UK appliance plug include a ground? UK 240 volt power has a neutral at zero volts, and a hot at 240 volts. In the US, our 240 has +120 and -120 volts, not quite the same. If you have a ground, that difference shouldn't matter, since the chassis would be grounded. Either way though, you want to check that your appliance isn't counting on the one side being close to 0 volts. Verify that your appliance chassis is close to zero volts, both when turned on and when turned off.
    – BaddDadd
    Mar 20 at 21:33

4 Answers 4

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What would be needed is a dual plug, such as this wall-tap has, but with only a single 240V outlet

Such a dual plug wall tap would be unreliable, because it can only work correctly on a MWBC.

If both sides of the receptacle are on the same (regular) circuit, your wall-tap would have 0V. If both sides are on different circuits, it is harder to impossible to guarantee that the wires take the same route from panel to receptacle and that the breakers are handle-tied.

As you state that you already have 240V at the location, a better option is to look for a 120V/240V receptacle combination. Then you can just plug in your European appliance into the 240V receptacle (with an appropriate plug converter) and it even leaves you a 120V receptacle as spare. See also the answers to Can I install a 240V outlet in my new US home for my UK kitchen appliances?.

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  • This answer diy.stackexchange.com/a/287326/140350 has both add-on and replaceable 120 & 240 North America receptacles. Mar 20 at 15:09
  • This dual receptacle would be perfect. Thanks. (And for those concerned, it's far enough away from the sink that a GFCI isn't needed.) Mar 20 at 15:35
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    Note that if the sides of the outlet are GFCI protected (common in kitchens), this won’t work. Taking 240 volts from a pair of GFCI protected 120 volt legs will immediately trip the GFCIs.
    – DoxyLover
    Mar 20 at 17:03
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    For a shared phase, you'd get 0V differential voltage while having two hot wires, right ? Fun times.
    – nick
    Mar 21 at 13:42
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Yes

There are several products that do this with a box and two input cords. They incorporate a monitoring circuit and relays to ensure the two inputs have incoming voltage with correct phasing before connecting the output. This prevents a shock from prongs of a disconnected input cable, the hazard identified by the OP.

One product, the Quick 220 is claimed to be ETL listed to UL 1012.

I was at a site which required these boxes instead of step-up transformers due to a history of shoddy transformers catching on fire.

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  • That's a bit more than an "adapter". It's a logic-controlled device.
    – isherwood
    Mar 21 at 15:56
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No inexpensive way to do this safely or reliably. (See user71659's answer for an approved device, but the cost and "no GFCI/AFCI" constraints are important.)

The reason 240V -> 120V works is the principle of the Multi-Wire Branch Circuit. This is a 240V circuit that uses one neutral together with two 120V hot wires that are on different "legs". That means there is 240V between the two hots, so you can power either 240V or 2 x 120V or both from the same circuit.

There are a number of safeguards involved, particularly to make sure that (a) if you turn off one 120V hot wire in the breaker panel that you turn off the other at the same time and (b) that the two 120V hot wires are on different legs and not on the same leg.

While using a crazy adapter is not the normal way to create a 120V receptacle on a 240V circuit, it is not inherently wrong. There is a current overload protection issue - e.g., using a 30A 240V receptacle to power a 15A or 20A 120V receptacle requires providing 15A or 20A overcurrent protection for the 120V receptacle, but that can be done. The cheap adapter cables are not UL or ETL listed because they don't provide this protection. However, this GE adapter from Home Depot:

GE adapter 240 to 2 x 120

does provide protection - a circuit breaker on each 120V socket.

However, going the other direction you have to make 100% certain that the two "source" receptacles are on opposite legs. That is easier said than done. MWBCs are relatively common in kitchens, but even then they could be configured for top/bottom in each duplex receptacle (in which case this type of adapter would work well) or for alternating duplex receptacles (i.e., the MWBC splits in the first receptacle box), which has the advantage of allowing for GFCI/receptacles to provide GFCI protection.

You are really much better off running a new 240V 20A circuit and installing a standard NEMA 6-20 receptacle. Then you can put a 6-20 plug on the end of the appliance cord and you're all set. But remember, this will need GFCI protection, which means a GFCI/breaker as GFCI/receptacles are only generally available for 120V circuits.

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  • The GFCI/AFCI limitation is a good point with those becoming far more prevalent over the last decade.
    – user71659
    Mar 21 at 5:32
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Yes.

If you are looking to power an ordinary single-phase 240V device, such as one that is used in a country where 240V is the standard line voltage (Europe, etc.), there is a very simple and completely normal solution. It's called a travel adapter (that is an Amazon link, I don't endorse them either way, but I take this as de facto proof that this is fairly common). Make sure the total wattage matches (the device must do more than 240 x # of amps drawn by the device).

If you want a 3-phase US 240V outlet, not without problems. In general, no. It is possible to do this but it is going to be complicated and much, much more expensive than running a separate 240V from the panel to your load.

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    The initial reason I would want this is to be able to use an electric kettle that will boil in half the time that is possible with a 15A 120V circuit. So a travel adaptor would not be of any use since it is limited by the available wattage. ¶ Also, while transmission lines are 3-phase, North American domestic power is not. It is 240V single phase, with the equivalent of a center tap connected to neutral (providing 120V with respect to each of the live lines). Mar 21 at 16:02

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