"Gary Coffman" wrote in message
...
On Tue, 27 Jul 2004 16:23:58 GMT, "William"
wrote:
"Gary Coffman" wrote in message
.. .
208 wye is common, but falling out of favor. Higher voltages are
preferred
now almost everywhere because they allow smaller wires to carry more
power (higher voltage, same current, more power). Lots of 480 3 ph wye
and 277 volt 1 ph. That means transformers are required to get 120 or
240,
but spotting dry transformers around the facility where low voltage 1
ph
is required while distributing power to them at a higher voltage saves
a
*lot* of copper (lot of money in any building bigger than a bread box).

Gary

Well that is true you can run smaller wire, but as I found out there is
a
dirty little secrete in the above plan. It's the transformers!!! I set
up
my shop that way and was going to run 480 volt to my house and step it
down
there ( smaller wire less cost, lower % voltage drop etc...) sounds
GREAT
on paper, well reality is that it's not cheaper at all! at the shop I
have
a 225 amp panel for 208 3phase that I use to feed the 5 ton air unit (
single phase) and lots of wall outlets. To run that panel NEC says min
75
kva transformer. Problem?? that transformer burns 600 watts at idle!!
just
keeping it warm! The house is even worse, planed to send 150 amps of
480
up to it, to feed a 300 amp panel. so ole NEC says I need a 112.5 kva
transformer. I have a nice 800lb copper wound K13 rated transformer,
and
it burns 1200 watts !!!! IF you could run a smaller transformer you
wouldn't have so much loss, but unlike the power co that will feed 5-6,
200amp houses with a single 50kva can, I have to follow the NEC:-(

Lets put this in perspective. Our plant's power bills average $20,000
a month. At 4 cents a kWh, we don't even notice the transformer
magnetization current losses. But we certainly noticed the $600,000
savings in wiring the plant by using 480/277 instead of 220.

Gary

YES lets keep the perspective! This is not rec.huge.factory :-) I don't
know many/any who have 20k per month power bills, and at the rate I get, it
would be 40k per month as I don't get power at 4 cents per kWh :-( Well
maybe I would if I burned that much ) The smaller transformer costs me
about $35 per month to keep it hot and the larger one will be about $75 per
month. So at about $1300 per year just to keep the transformers hot adds up
FAST. For smaller users the wire cost is not that great. The largest motor
I have is 20 hp and the savings just are not there... If I had it to do
over I would have let the power co provide a second feed for the lower
voltage and only single phase, it would save me a lot of cash and let them
heat the transformer on their dime... That way I would have the cheaper wire
where needed, and the best of both worlds

William....