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The adapter shown in the picture is described by the seller as "4-Prong 220V 14-50p Outlet Plug to 120V 5-20R/15R Female Adapter Power Cord for 20V [sic] 15/20Amp Household W/Breaker".

What I would like to do (if it is feasible and safe) is to convert a 4-prong 220V 20A circuit (USA split 2x120V) into a single 120V 20A circuit by plugging into the ground, neutral, and only one of the hots. Can one hot leg of a US 220V 20A circuit be used and the other "ignored" as shown in the second (doctored) photo?

220V (US) to two 120V outlet adapter cord

220V (US) to single 120V outlet adapter cord

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  • If this did work, won't the power output be pins rather than a socket? That does not appear to be very safe. Normally power outputs are in sockets rather than pins so they don't easily make unintended contact.
    – user4574
    Aug 16 at 13:24
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    @user4574. The pins shown in the photo would be plugged into a 220V outlet and the female outlet shown in the photo would become the output. There would be no unintended contact from exposed pins, since there would be no pins exposed.
    – mr blint
    Aug 16 at 13:27
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    All you need to do is use one of those sockets and ignore the other ... or fit a blanking plug. Aug 16 at 13:48
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    Why do you need to modify the cable? Why not just buy it and plug it in?
    – Mark
    Aug 17 at 15:32
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    I'm a little confused about what the course of action you're considering is. Are you considering using the actual cable pictured as is; or are you considering taking the pictured cable and modifying it so that it's like the doctored picture; or are you considering making your own cable similar to the one in the doctored picture; or are you considering changing the wiring in your house and installing a new receptacle? Aug 17 at 17:32

3 Answers 3

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It should work as long as the 240 VAC outlet has neutral connected and the correct wire gauge. Some only have the two hots and ground. A four wire one should have both neutral and ground.

This is basically how 120 VAC wiring works, each outlet or light fixture is connected at the breaker panel to one or the other hot, and the neutral and ground. So if you've got the hots, neutral and ground at the 240 VAC outlet you should be able to just use one hot to get 120 VAC.

I don't know if that would violate any local codes, you would have to check into that.

I believe the purpose of the four wire outlet is so that things like dryers can use the 240 VAC for the heating elements and also have 120 VAC available to run the electronics.

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  • In your first sentence, "the outlet" refers to the 120V outlet? I'd bring neutral, ground, and 1 of the hot wires from the 220V circuit to the 120V outlet, with the same gauge wire that was used in the 220V circuit.
    – mr blint
    Aug 16 at 19:43
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    I meant the 240V outlet. Basically saying that as long as neutral is available it should work.
    – GodJihyo
    Aug 16 at 20:02
  • Just FYI, the tumbler motor on many (if not most) clothes dryers are also 120v. Never heard reasonable explanation why. Aug 17 at 14:48
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    @NoSparksPlease Probably just for parts commonality with gas-heated dryers. Doesn't make sense to design and source two different tumbler motors when they can be the same.
    – Chris O
    Aug 17 at 15:04
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This was too long for a comment. In addition to GodJihyo's answer, be aware that if this "outlet" indeed splits one "hot" to one receptacle and the other "hot" to the other receptacle, some devices may not play nice between the two receptacles.

Imagine this: you plug this 240 V cable in, then plug in a no-name 120 V to 12 V battery charger into hot "A". So far so good, the battery is being charged. But it isn't charging fast enough, so you plug another no-name 12 V battery charger into "B" and also connect this to the battery. The moment the positive leads touch, both chargers (and the battery) explode. What happened?

The answer is that hots "A" and "B" are both 120 VAC, but one is 180° out-of-phase with the other. It has to be, for the sum of them to equal 240 VAC. So during every AC cycle, while A is positive, B is negative and vice-versa. In the case of these no-name battery chargers, their electronic controls were not designed with the vision that sink currents might peak when source currents valley and vice-versa. Such a condition upsets their stability, resulting in shutdown, failure, fire, etc.

Now I don't know if a no-name battery charger like this really exists, but it probably does (the cheaper, the more susceptible.) This is a design criteria which may be often overlooked, especially on cheaper electronics.

In most of my experiences of mixing A and B devices, any failure that does occur is usually more in the "severe" category rather than the "simply shuts down" category.

But I can say that some live pro audio gear (mixers, instrument amplifiers, etc.) are susceptible. Once a modern instrument amp was connected to an extension cord then patched into the mixer. The moment that (audio, 1/4" tip, supposed to be high-impedance) connection was made, it sparked and killed both devices. The outlets were wired fine - the issue was mixing hot "A" and "B" outlets due to the extension cord. After being electrocuted on the lip from a "bad" extension cord also, I'm very careful of extension cords and unfamiliar outlets. Learned to carry an outlet tester (the hard way.)

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  • If I understand correctly, you're envisioning two (2) 120V outlets, right? But I'm proposing just a single 120V outlet.
    – mr blint
    Aug 16 at 19:37
  • Right, I'm just saying to remember that the "other" outlet is special and generally should be avoided. Even if you remember, someone else may come across it someday, remove the blanking plug, and connect another device.
    – rdtsc
    Aug 16 at 20:26
  • Edit: if you were asking about building your own version of the shown cable but using only one "hot" and one outlet: yes this is safer... but only if the cable is short and the user isn't tempted to go connecting it to a second no-name battery charger (because you have no way of knowing which "hot" each device gets.)
    – rdtsc
    Aug 16 at 21:40
  • I don't understand the problem. A battery charger or most any AC powered device will have a transformer followed by a full wave bridge, or for a switching type it will be a FWB into a capacitor followed by an H-bridge and high frequency transformer. If the loads are balanced, the neutral current will cancel. A half-wave rectifier might pose a problem, but only if one is connected with reverse polarity, and I still don't see a problem other than net DC current draw from the mains. Please illustrate the problem.
    – PStechPaul
    Aug 16 at 22:12
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    Devices that expose line volatage on the output (like the hypothetical battery chargers) are wildly unsafe and should not be used, period. It is entirely legal to have the top and bottom sockets in a duplex receptacle fed from different legs, or two receptacles in one box fed from different legs. That is to say, the devices are already unacceptably dangerous in the face of totally normal home/office wiring. The cord in the question really isn't doing anything new.
    – nobody
    Aug 17 at 2:03
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The physical configuration of getting 120v from a 240v receptacle is correct, but the amperage available is a critical consideration. The critical component in the build is the little red overcurrent button.

The 14-50r is likely on a 50A breaker, which if operating within specs could let 100A of current flow for about 2 minutes without tripping. That little overcurrent device could be all that is keeping a faulty 18/2 cord plugged into that receptacle from melting and becoming a fire starter.

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  • The actual 240V circuit involved is 20A. I was thinking of a cable analogous to the one shown but with the appropriate NEMA plug for a 20A 240V circuit. Since it is only a 20A circuit, I have only one 120V outlet in the "doctored" photo.
    – mr blint
    Aug 17 at 23:40

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