If all you have is two wires, its single phase. It may have come from
split, or a 3-phase setup, but all you can get with two wires is single
Now, if you have *three* wires, measure the voltage between each
combination. If one combination is exactly double the others, then you have
a 'split' or 'Edison' connection (like a typical US residential service).
(for example 120-120-240)
If the voltage of one combination is 1.73 times the others, you have the
neutral and two legs of a three-phase wye. (for example, 120-120-208).
If the voltage is exactly the same each way, you have three-phase with no
neutral. Could come from a wye, or delta feed.
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