120v any different on 3phase than 1phase?

Hi, No.

You are so right. :-)

I get the feeling you are doing this on a commercial installation.

That is a scary question coming from a commercial electrician.

They have 3phase to power some very large pumps. I wouldn't touch any of that. This is just a simple 120v water heater; as long as it is the same as

Check the leg with a volt meter before making the connection. To balance the vectors in 3-phase, one leg has a higher voltage. If you already have a 120 volt panel, the installer will have taken care of this for you.

Not if it's the 120/208V Y three phase that is found in nearly all light commercial buildings. Delta configurations which may have the high leg are typically found in industrial buildings.

I get the feeling this is a DIYer or a non-electrician handyman, most likely in an apartment building, though I'm told there are rare cases of single family houses near commercial areas which are supplied with

120V water heaters use more amps than the more common 240V ones, so I'd recommend the OP double-check the ampacity of his cables and breaker.

Chip C Toronto

High legs are sometimes found in 240V Delta connected transformers.

The only time I ever worked in a building where there was a high leg, there was one panel for 3 phase only and a separate panel for single phase. The single phase panel only had the two phases that gave 120V to neutral so there was no way to end up with 190 to neutral.

Larry The kind of power arrangement you are talking about is rare and absolutely forbidden inside a dwelling unit in most places. The only time he would have one leg with a higher voltage to ground would be on a delta connected transformer secondary supply. Since the OP specifically said it was Wye connected I don't see were you get the idea that there is a high or "stinger" leg involved.

The OP did not say it was a wye configuration. He also did not say it was a residential installation. He did say they were running some large pumps. If they are after a rotating magnetic field, a delta configuration is likely. In any case, it won't hurt a thing for him to stick a voltmeter on the lug to see what voltage he really has.

He said it was "The panel is 120v/208v" which automatically tells us that it is a wye configuration, since there is no such thing as a

My house in Dallas, Texas has Wye 3 phase power.

-- Doug