Harold and Susan Vordos wrote:

"Pete C." wrote in message
...
Don Murray wrote:

Harold and Susan Vordos wrote:

"William" wrote in message
news:fQire.47092$_o.36229@attbi_s71...

"Pete C." wrote in message
...

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.

Huh? What "obvious reasons"? 120/208 Wye service has no disadvantages
that I know of. You can get 120v from any of the phases, allowing you
to
balance your single phase loads and single pole, two pole or three
pole
breakers breakers can occupy any panel position since all phases are
equal to each other and to the neutral.

Well there are disadvantages from the 208 voltage, a lot of motors
will

not

run at 208 with out overheating them. And my band was blade welder
didn't
really like it either, had problems welding the larger blades. The
oven
elements also don't seem to get as hot, cloths dryer, etc.....

William...




Exactly! I'm still at a loss to understand why the delta system
is
such a problem.
Seems to me the Wye system, *for a machine shop*, would be far more
disadvantageous. You'd have to be completely out of your mind to
request
it if delta was available.

Harold



You're right, Harold. I think the 3 transformer delta service is the
better of the two. One advantage is that when one transformer goes out a
trouble shooter from the power company (me) can go out and rebuss it
into an open delta and have you back up and running in 30 minutes. The
two transformer open delta is only good for 86.6% of the KVA rating of
the two transformers. So you might have to shed some load.

You should also be able to replace the transformer in about the same
time period. I watched a crew (two guys in buckets and one ground guy)
change one in about 15 minutes. Even with the first guy (you) getting on
the scene and then calling in for another truck to bring out the
transformer while you remove the bad one it should not take very long.

Pete C.

Chuckle! You, apparently, live in town. Not only could they not replace
one for me in 15 minutes, it's highly unlikely they could do so in a couple
hours. It would take no less than 45 minutes for someone to respond to
our remote address, then the time it would take to get a transformer on
location, assuming they had one in the yard.

That case was indeed in town and it was a planned replacement. However,
if you give them sufficient information when you log the trouble call I
see no reason they couldn't have the correct transformer with them when
they come out. Given the stock yards I've seen I think it's pretty
unlikely that they would not have a suitable replacement on hand. So 15
min to replace + travel time to get there.


Yeah, I know, small chance it would ever be an issue, but it's yet another
one of the things that make me sure I did the right thing. I say go with
the wild leg delta! In my experience, many of the older machines had
motors wound for 240V, not 208V. That tells me they would be inclined to
run hot. Do keep in mind I am not an electrician, so my exposure has been
quite limited. Could be I'm all wet.

Well, the motor (original) on my old old 1J Bridgeport is 220/440 rated.
Looking at the Grainger and Baldor sites I was not able to find any 240V
rated motors. I suspect you'll find the machines have 220V or 230V rated
motors.

The difference in current draw between operation at 208V and 240V is
quite small and only a portion of that difference would be dissipated as
heat. For a 2 HP Baldor motor I looked at the total difference was 104W
and even if all of that was dissipated as heat across the 60# motors
frame it would be pretty insignificant.

Most all motors are going to run hot on continuous duty and that's why
they have the different insulation classes. If the motor runs 4 or 5
degrees hotter on the lower voltage it's not very significant.

Pete C.