Gary Coffman wrote:


Nope, you took that one out of a different context. I'm talking about 208 delta
there. Your power company may still support it for new work, but none of the
ones I know will (though they continue to support it in old work). They want
to supply 480 wye instead. It saves them money via smaller cheaper transformers.
In a stretched out facility it saves you money too, in reduced copper costs.

Gary

Gary,

I don't think I took anything out of context, I am going to cut and paste the
paragraph from your original post so you can see why I thought you were talking about
208 wye.

"Note you probably don't want to change to 4 wire wye service.
That would give you 120 volts to neutral from any leg, but the
leg to leg 3 ph voltage would drop to 208. That would require
rewiring all your 3 ph motors for 208 instead of 240. This was
found a lot in older installations, but most power companies
don't want to provide this any more."

I've never heard of a 208 delta, other than the high leg on a 240 bank.

The determining factor in whether you will get a wye or delta secondary is the voltage
of the service. You can see the wye secondary transformer connections on my web page
have the secondary coils paralleled. What determines whether the high side is delta or
wye is the actual primary voltage of the line and the nameplate rating of the
transformer. Where I work, we have a lot of 12KV primary and a 20.8KV primary that we
use the same transformers on. The company stocks a lot of 12KV 120/240 transformers.
So if you are going to hang a bank to serve a 208V 3-phase service in the 20.8KV you
pop the lid off the transformers, parallel the secondary coils, and hang a wye-wye
bank. If you wanted a 240V 3-phase bank in the 20.8KV, it would be a wye-delta. If you
are hanging these 12KV transformers in the 12KV primary, it would be a delta
high-side. And again the secondary configuration would be determined by the secondary
voltage you want, 120-208V requires you to parallel the secondary coils and wye the
secondary side. 120-240V would be delta secondary.

The 20.8KV system is a common neutral system. That is the neutral carried in the
secondary position is shared by the primary and secondary, and is a metallic return to
the substation.

Don