John
You mention in thi reply below that you have seen a corner grounde
system in a DC^ aircraft. That surprizes me. Most other aircraft use
120/208 3 phase Y configurations.
Maybe I dont understand whata corner grounde is. I thought it would be a
delta with one corner grounded.
Jerry
"john" wrote in message
...
George wrote:
john wrote:
I always assumed that it was done for convenience. I have 3 hot wires
(A, B & C(wild)), I can run all my 120 stuff off A to neutral or B to
neutral. I can run all of my 240 single phase stuff off A-B and I can
run all of my 240 3-phase stuff off A-B-C.
Anything that uses 220 only, ( 220 with two conductors and a ground) can
be run off of any two legs. Only if the thing uses 120 and 240 volts
and has a neutral wire going to it do you need to use the centertapped
phases.
If I had Wye or corner grounded delta service then I would have to
give up one of those conditions or purchase another transformer.
Nope
One thing that is common in warehouses here is 208 Wye service. That
gives 3, 120 Volt legs. Obviously, I can run a 240 3-phase motor on
that service but it will only run at 208/240)^2 = 75% power. Worse
yet, many electronic items just simply will not run.
Thats one of the nice things about using 240 volts. Overvoltage is
usually less harmful than undervoltage
Alternatively, I can get 240 Wye service and run my 240 stuff at full
power. As you mentioned, you can always run 240 single phase stuff
across any two legs. (I can also use my 208V light bulbs from the
previous example) But how do I get my 110V toaster oven to work in
that arrangement?
I've never run across a 240 volt Wye supplied from an electric company.
IF you had a neutral supplied with the Wye connection you would have
120volts for your toaster.
a delta connection would require a transformer if there were no center
tapped transformer.
Same question for a corner grounded delta arrangement?
the only place I've ever seen a corner grounde system was in a DC-6
aircraft, and that was 115 volts leg to leg.
By the way: center tapped delta service is very common here in the
Chicago area. Wye service is strictly used in office buildings and
warehouses.
Everywhere I've been it was the same. 208 Wye was used where most of
the loads were 110/220 single phase in apartment buildings and stores,
otherwise it was 240 volts
red leg delta service.
you neighbor may be on a different pole transformer. IF he is then his
phasing is different than yours.
Yea, I figured as much.
We had an electrical storm here several years ago. Half the light
bulbs in the building were getting dim while the other half were
getting unusually bright. Then some of the bright bulbs began to
blow. I figured that we must have lost the center ground and that the
voltage was being split somewhere in the middle of the center tapped
leg. No doubt based on the relative load on either side.
I ran round the building frantically shutting everything off as light
bulbs popped all around me. I then called the electric company and
explained the situation. I must hand it to them, they arrived in truly
record time!
But I noticed that my neighbors lights were also bright in one window
and dim in the next. I was just sort of pondering the fun that it
would be to ground out one side of the transformer and then ground out
the other side.
Com Ed arrived before I worked up enough nerve to put theory to
practice.
I had the same thing happen in florida caused by a lightning strike. It
was like in the sci fi movies.. the fans were going up and down in speed
and the lights were flashing, It happened a day after the storm. The
day before they changed the fuse on the pole and i told them there were
other problems. I could smell the burned transformer oil.
John
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