Good morning electrical geniuses, here's a problem for you.

I have a piece of equipment that requires a 220v connection, and I do not have the ability to run a 220v line from the breaker. Is there a Y adaptor I could buy to combine 2 different phases of 110v to create a 220v power strip? all of the 110v outlets that I have access to are 20a breakers, so would this new 240v line give me 40a (assuming the hardware and wire gauge can handle it)?

The hardware is going to draw something in the neighborhood of 3200w/15a @ 220v (3200w/30a @ 110v), so if I combined 2x 110v/20a with a high gauge Y adaptor, I shouldn't have any problem as long as the wiring was correct?

I'm not an electrical engineer, I'm a mechanical one... Help, please :)

Edit 1: @ThreePhaseEel Here are photos of the electrical panel. The room with my specific panel is locked, but this is one of 3 identical rooms per floor, 4 floors. The room next to mine is occupied by someone who only has things plugged into the walls in the room, so if our bathroom receptacles are connected It won't matter. Breaker Panel for the Posted Description Breaker Panel Description Overview of Whole Panel

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    (1) And what will happen when some hapless person unplugs one of the 110 V plugs and finds that the pins are live? (2) 20 A out on one line is 20 A back on the other. There is no current in the neutral so you don't get 40 A, you still get 20 A. Do it properly. – Transistor Aug 24 '19 at 16:56
  • Thank you for a quick answer. I understand the dangers behind that, however, this is a 1 room apartment effectively and I am the only occupant. I have the ability to secure the plugs to the wall. I understand now that the Y setup would give me 20a, however, would it be possible to do 2 Y adaptors on 3 different breakers, and use those 2 separate 220v 20a circuits? I realize this would double the strain on one of the outlets, but would it be dangerous? It shoudl evenly split at 15a per circuit? – Evan Ledwith Aug 24 '19 at 17:12
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    @JRE -- and replace the two breakers with a single two-phase breaker or add a mechanical link between the two breaker handles. – Pete Becker Aug 24 '19 at 18:13
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    I have down voted this question to alert to the fact that this should not even be considered. – Michael Karas Aug 24 '19 at 18:58
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    Handle ties do not work that way @JRE, they are not capable of providing common trip. They give common maintenance shutoff only. On a 2-pole, the common trip mechanism is internal and has nothing to do with the factory handle tie. – Harper - Reinstate Monica Aug 25 '19 at 0:31

Huge problems with this. Gigantic.

If a breaker trips, you'll be backfeeding the tripped circuit.

"What could go wrong?"

So your machine is loaded between circuits A and B, and SNAP! Circuit A breaker trips. Your machine stops working, of course.

But what happens to the other loads on circuit A? They're dead right? No sir, they are not. Power from circuit B is traveling through your machine and ending up on circuit A. Now, it's pulling circuit A's voltage toward circuit B's voltage.

What does this mean for other appliances still plugged into circuit A? Oh, they're getting power alright, from circuit B through your machine. So they're going to power back up, even though one of them just tripped the circuit. But it will be weird, because those appliances (together) will be in series with your machine. So voltage will be rather wack-a-doodle, and that can cause problems for some machines.

You insist that nobody will be affected but you. Except you want to tap a circuit that's shared with your neighbor. Which means not only could they cause the breaker trip, they could be the victim of the above effect.

Current will be traveling in a big circle.

And that's a huge no-no when you are dealing with AC power. That is because AC creates inductive effects - this is the reason transformers work. You are causing high EMFs, which in turn cause vibration, which causes fatigue and arcing failures, and eddy current heating in anything metallic anywhere near the imbalanced wires. And the wires are running through all-metal conduit. That reduces the chances of fire, but wildly increases the eddy-current losses; you're essentially turning the conduit wiring system into a giant electromagnet. That could cause voltage drop at the appliance, which for a switching power supply will cause it to draw even more current. So all of your numbers could be wrong.

These eddy currents/heating/rattling-vibration problems are much worse at higher currents. And you are planning to run this circuit near limits.

Two plugs on the same cable

You're violating the "No cable should have two pointy ends" rule. The reason for that rule is it's possible for one to be plugged in while the other is in your hand. So that means you can get nailed by it, since one prongy end plugged in will make the other prongy end hot. You can trip over a cord and pull it out and have it hit you. Or it can short against equipment, causing arc damage (kind of a big deal in a rental) and potentially starting a fire. There is no (practical) way to make this thing fully de-energize until both plugs are plugged in.

Oh, snap. It's not 220V anyway.

Dude. You're in a large commercial development. You don't have "220V" (actually 240V). You have "190V" (actually 208V) 3-phase. When you figure the additional losses from turning your building into a giant electromagnet, say your practical voltage is 180V.

Now take your "3200W" load. Is that load really 100% power factor? I kinda doubt it. It's probably more like 80% power factor, which means if it's drawing 3200 watts, it's drawing 4000 VA. VA is the number we have to worry about with breakers and provisioning power.

So your 4000VA into 180 useful volts - you are now at 22.22 amps. Whoops-a-daisy. Even if we assume ideal 208V, you're at 19.2 amps. Even a power factor of 95% puts you over 20 amps!

Now, you're not allowed to run circuit at 100% (or 96% as would be the best case here). Your maximum continuous load can only be 80% of circuit capacity - or 16 amps.

Even if the circuit was perfect, even if you had no losses, even if your power factor was 100%, your ideal load at 3200VA/208V = 15.38 amps. Even at 96% power factor you're a tick over the permitted 16A.

In other words, not even close.

But go read your machine's labeling and instructions and see what it says about 208V operation.

You can get a 240V^H^H^H 208V circuit anyway

The thing about this building is, it's a commercial building. It's wired in metal conduit. That means a competent electrician can fish a couple of blue wires through the existing pipe, and hook you up with a 208V dedicated circuit that's all yours. It can be a 20A circuit if your device is able to work on that (given the above provisos), or a 25A or 30A circuit if the numbers show that it needs that.

So the right answer here is to ask management for the service you need. It's not far out of their way.

They even make a "dual voltage" 120V/208V receptacle that can go in any normal (non-GFCI) receptacle location. That will comply with certain Code requirements that require 120V receptacles at a certain spacing.


Do not do this with your idea to make or get some type of Y-adapter. It is just too crazy dangerous to do this. In addition the fact that you have to ask this question here to learn about it is a demonstration that this is not a good idea. There are many factors that have to be considered and even in a few comments under your question not all of those factors will come out in discussion. This will leave you thinking that you fully understand the issue when in fact you would not.

I know you claim that you have control over things and that you would subscribe to the safest handling of a kludged up connection system .... but STOP here. Do not do this.

Hire an electrician to do this properly. I know you said you have to wire this yourself but I suspect that you say that because you may not even have legitimate grounds to even consider changing the wiring. The community nature of your building with power panel behind a locked door seems to indicate that you do not have the free right to go changing things like this.

Sorry to have to sound so harsh about this but crazy ideas like this have to be stopped before they get out of hand and someone gets hurt, killed or serious property damage occurs.

  • Excellent analysis and safety advice! Moreover I don't feel confident that the electrical system of a single room in a community building could happily tolerate a 3200W load on a single socket for long periods of time, unless the system is new and the designers were exceptionally "generous" for the wiring (I admit I'm not used to USA electrical systems practices and regulations, though. So my "feel" could be misplaced). – Lorenzo Donati -- Codidact.com Aug 24 '19 at 23:00
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    Thank you for the advice. Harsh or not, I have no doubt you are correct. The building was built by contractors for the U.S. Government, so the wiring was PROBABLY skimped on. My room is however designed for 2 people to live in and factored in for more than normal personal electronic devices. Heeding the advice everyone on the ENTIRE internet, I will take my 240v wye adaptor idea and save it until I get an electrical engineering degree. I am able to power everything using 110v, by using more power supplies and spreading the load. – Evan Ledwith Aug 24 '19 at 23:17
  • @EvanLedwith -- don't bother with Y adapter nonsense, period. There are far better ways to do it in your permanent wiring (basically, using a properly configured MWBC) – ThreePhaseEel Aug 24 '19 at 23:29

I have done this before, and it worked perfectly. All of the other offered advice in the comments are valid, as this can be dangerous if someone besides you will be around that could be handling your cabling. As mentioned previously, you would have to source your current from two different outlets that are out of phase with each other, and the total current available will be that of the lowest value breaker on the two circuits, in addition to any other load on any one of the two circuit breakers.

Just to clarify again, I have successfully done this, but it is not recommended, and should only be attempted temporarily in carefully controlled situations...

  • You got lucky. That could go stupidly wrong. – Harper - Reinstate Monica Aug 25 '19 at 5:36
  • @Harper - Not sure how that could go "stupidly wrong". I wired all four outlets on the wall behind my workbench with the 1st and 3rd outlets being on one phase from my breaker box, and I wired the 2nd and 4th outlet to the other phase, in order to somewhat balance the load. When I needed to test a 220 volt device one time, I double checked the phases with my 2 channel oscilloscope, and then wired up an insulated combiner cable. Checked the cable with my oscope after it was done, and, bam!, 220 volts ready to power my target.... – Hitek Aug 25 '19 at 6:11
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    That's why "EE" and "licensed electrician" are different trades :) Naturally there is a subset of EEs who specialize in AC mains power; some of them work for NFPA who writes the electrical code. In fact they provide a way to do that thing you did; it's called a "multi-wire branch circuit" and it even saves $ on cable. In a MWBC you put 120V receps between either hot and neutral, and/or 240V receps between hots. They even make special duplex recep's with one each NEMA 5 + 6 on the same yoke. The mains boys have it figured out :) – Harper - Reinstate Monica Aug 25 '19 at 6:29
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    I think most of us are afraid that even if there's a corner case that merits a dodgy technique, and we advise it, other people will read it and think it's OK for them too. A huge percentage of our visitors are reading old questions for advice. For me, that turns into the idea of "permanent wiring that's temporary", i.e. Do it like it's forever, then undo it like it's forever tomorrow... – Harper - Reinstate Monica Aug 25 '19 at 7:25
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    @Harper - OK, I added a solid stipulations warning to the end of my answer. – Hitek Aug 25 '19 at 7:40

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