Harold and Susan Vordos wrote:

"DoN. Nichols" wrote in message
...
In article .com,
wrote:
Can you get 120v single phase by picking off one line of 240v 3 phase
as long as you have a neutral to carry the current back to the box?

Not quite. The voltage won't be right for pure three phase. I
think that with Wye connections, you will have something closer to 104V.

I'm at a loss to understand that, DoN. Care to elaborate? I have wired
three places with delta service, two of which used either the A and C phase
and the neutral for 120V. All of it was done to code. The third place
has a single phase panel along with the 3 phase, both of which are fed from
the same taps from the transformers.

If it had a neutral it wasn't a delta service.

The 104V mentioned was a typo, it's really 138V and change. Square root
of three thing for three phase power. 240V Wye service will give you
138V phase to neutral and 208V Wye service will give you 120V phase to
neutral.



And many are delta which *has* no neutral. All may be floating.

In this case, he's already suggested that there would be a neutral, so it
would be a 5 wire system.

Known as Wye.



But a frequent variation has one of the three sides center
tapped (the way the standard residential feed is supplied, 240V center
tapped with the center tap grounded and neutral connected to that.)

The breaker boxes for this have three buses, but only two of
every three positions can be used for 120V single-phase breakers. The
third phase is *way* too high.

I believe this is often referred to as the "wild" leg.


As stated above, I got around that problem in my current shop by having two
panels, one strictly 3 phase, so none of the positions are lost.

There are / were a lot of strange variations on three phase power, but
most anything new is going to be 208V Wye service. Larger industrial
stuff will get 480V.

Pete C.