wrote in message
...
On Fri, 02 Feb 2007 15:13:46 -0600, Mark Lloyd
wrote:

. It is even weirder when you have a three phase delta system
with one side center-tapped and grounded. It is one of those
unfortunately
ambigious situations where the language is sometimes not precise enough
to
clearly describe the situation. People have been disagreeing and arguing
this point forever and probably will continue forever. It is not a
disagreement about the facts, but only "What is the nameof it?".

Don Young

Right.

I'd find that 3-phase delta system confusing too.


It is just a garden variety single phase 120/240 transformer that they
add a second one to and trick motors into thinking it is 3 phase.
Generally they don't use the 3d transformer to make a true delta.
If they wanted to spend that much money you would get 3p wye.
You see it in light industrial areas where most of the load is single
phase on a big 1p transformer and a second only supplies the "red" leg
for the 3p load. (actually identified orange) As long as you never put
L/N loads on the 208v red leg it works fine.
I have seen a lot of the two transformer open delta and three transformer
wye services, but I have also seen quite a few three transformer closed
delta systems. It seems to depend on the relative loads. The open delta
seems to be used where the three phase load is fairly light and the closed
delta where there is a heavy three phase load but 120/240 single phase
service is also required. It may be a regional thing and I think the delta
connection is becoming rarer and is being replaced with a separate single
phase transformer where 120/240 is required.

Don Young