View Single Post
  #10   Report Post  
Harold and Susan Vordos
 
Posts: n/a
Default


"Pete C." wrote in message
...
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.


Wrong!! One can have a three, four or five wire delta system.

I have a 5 wire system, and it *is* a delta system. It is not a wye, which
does not have the wild leg. Mine does have. Ground is established by
tapping the center of one coil, which results in the longer path to ground
from the other two coils. 208 volts from phase to ground. It's not
conjecture, it's measured.

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.


Again, wrong. It *is* a delta system. He's talking about 240 volts, not
208. As far as I know, single phase service to the typical house is just
one leg of a three phase delta system. Isn't that how it comes from the
power plants, the primary service? How it's delivered to the customer
depends on the transformers that feed them.



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.


Agreed.



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.


My 3 phase delta 240/120 volt service was installed just 4 years ago, at my
request. I did not want a wye service (for obvious reasons), and am
transforming to 480V for one machine.

Harold
..