[bombela]

You can feed a US outlet the split phase 240V and get two 120V@20A each.

It used to be done in kitchens in the US, back when appliances were power hungry. I have done so in my workshop for the same reason.

Houses are wired in split phase 240V, with the neutral in the middle. That is, you have two opposite 120V phases, around the same neutral.

This is a clever way to double the power, while adding a single wire.

In the US the standard outlet receptacle has two outlets. Bring the same neutral to the two outlets, and assign one phase per outlet (outlets have metals tabs you can break off, you don't need any extra wiring).

At the panel, you have a dual breaker. One breaker per phase, with a physical linkage forcing them to trip and arm together at once.

As a benefit; but very unsafe; you can make up a Y that plugs into the two 120V outlets, and gives you a single 240V receptacle. This is unsafe because if you plug only one of the 120V plug, the other one has now 120V on its exposed phase prong! On the other hand, I have both 240V@20A and 2×120V@20A anywhere in the shop ;)

[amluto]

Skip the Y hack and do it in style, legally!

https://store.leviton.com/products/duplex-receptacle-outlet-...

[bombela]

I am aware of this. But then I have a single 120@20 vs a single 240@20.

With my setup I have 2×120@20 always available, and 240@20 for the occasional welding.

I could assign a different 120 phase to every other outlet but then I would need some clear identification.

The two phases are assigned to the top and bottom outlets the same way all around the shop. If I need to run two high amperage machines, I only have to remember to use one bottom and one top outlet.

[mindslight]

If you're talking about a workshop and anticipating that much ad-hoc power usage, I'd just put two dual 6-20 receptacles side by side rather than splitting one. And then since you're actually creating the premises wiring, stick an (L)14-20R next to them in parallel and get rid of your need to fuss with hacky combiner cords. At least that's what I plan to do when I have the time for such luxuries.

[bombela]

I only very rarely need 240V, if I had permanently mounted 240V machines or frequent needs, I would do exactly what you propose.

[oasisbob]

GFCI requirements will interfere with the legality of many modern-day multi-wire branch circuit plans, yeah?

[amluto]

You can get a two-pole GFCI breaker for this purpose. The prices are a bit silly.

[bombela]

two poles breakers, 2×120V@20A, $USD:

    - $20
    - GFCI, $115
    - GFCI + AFCI, $115

Yes it is expensive, but it can also save your life.

[amluto]

Many things can save your life. Most of them don’t have a UL-provided monopoly making it quite unpleasant for anyone to compete to produce the version that fits where you need it.

A 1-pole GFCI breaker, a 2-pole GFCI breaker, and an ordinary GFCI outlet all have the same clever pair of coils, the same IC, and rather similar trip mechanisms. Yet the costs are quite different, and the costs get _really_ absurd if you want a breaker that trips at a level other than ~5mA.

And yes, they’re all very much worth using. I do wish that electrical codes would at least start encouraging the use of GFCIs for 240V outlets, which might encourage manufacturers to start making them, and those would actually be able to compete with each other.