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EDIT:

Let me re-phrase the question, as I did a terrible job the first time.

I have a mill that can definitely run at 220v, with two legs of 110v, (split phase, as commenters have informed me). I've run it from both a drier plug (split phase 110v in canada), and a variac (split phase 110v.). The nameplate also says 240v.

I bought a 2kw transformer (perhaps an autotransformer?) that provides 240v, single phase.

Is it safe to connect these?

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  • \$\begingroup\$ sounds like a step-up transformer? \$\endgroup\$
    – user16324
    Aug 23, 2016 at 15:33
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    \$\begingroup\$ "what to call two legs of 110v, adding to 220v?" - Split phase :) \$\endgroup\$
    – marcelm
    Aug 23, 2016 at 15:45
  • \$\begingroup\$ marcelm got it right. It's simply called split-phase. Here's a question I wrote using that in its title: electronics.stackexchange.com/questions/252067/… \$\endgroup\$
    – jonk
    Aug 23, 2016 at 16:23
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    \$\begingroup\$ Can you use the schematic editor to clarify your question? In particular, I'm wondering about your measurements with the 2kw transformer, where you say you got 240V to ground. If the secondary has only two wires and if you measured from each leg of the secondary to ground, then you didn't really have a galvanic circuit, at all. And I'm not sure I trust what you read. So I'd like to have that measurement clarified. \$\endgroup\$
    – jonk
    Aug 23, 2016 at 16:25
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    \$\begingroup\$ If the machine requires only L1 and L2 with no neutral, and has a ground connected to the metal parts of the machine only, not any part of the circuit, then it doesn't matter how you get 220 volts for L1 and L2. If that is not the case, the solution is more complicated. Also, you need to find out if the outlet can safely supply the required current. \$\endgroup\$
    – user80875
    Aug 23, 2016 at 18:17

1 Answer 1

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If you have a two phase system with L1,L2 each measuring 110VAC to ground, then try to measure the voltage between L1 and L2. If the phases are lagging by 180 degrees you should get 220VAC, no transformer is needed, just connect the ground, L1, L2(instead of neutral). Make sure neutral wire is isolated from ground.

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