Personal would be on the ground seems to me.

Small company ? - larger one ?

Building contractors put them in neighborhoods - have overages ?
Cosmetic ?

Martin

On 10/26/2010 8:12 AM, Pete C. wrote:

john wrote:

Karl Townsend wrote:
On Mon, 25 Oct 2010 23:28:06 -0400,
wrote:

Pete C. wrote:

Jon Elson wrote:

On 10/25/2010 02:58 PM, Karl Townsend wrote:
"The Kid" is putting in underground wiring to his outbuildings. For
now, power will come from the house to the shop.

The shop sits twenty feet from a three phase line. future plans is to
install a three phase service to the shop, cut the ordinal transformer
out, and then feed one phase back to the house from the wiring being
installed now.

OK, a one phase house service has two 110 legs on the same phase
opposite polarity to get 220 across the two hot wires, neutral is the
center tap. As I understand it you in effect get three 110 hot wires
120 degrees apart in the phasing for three phase with the center tap
for neutral.

So, can you run single phase 220 off this? Need any special provisions
installed now? He's putting in conduit - four wires - two hot, neutral
and ground.
There are essentially 4 ways to wire a 3-phase 2xx Volt service.
There is 240 V delta, and 208 V Wye service. 240 V delta is not what
you want here. 208 Wye service will work, but if you hook the house
to 2 of the 3-phase hots, you get 208 V on the appliances that expect
240. Check the air conditioners, etc. carefully for their ability to
run off 208.

Then, there are two variants of the above systems, you may not be able
to get these installed by your local electric company. One is
corner-grounded delta, that gives you 2 240 V hots, good for running machine
tool motors, the advantage is you can use normal 2-pole electrical
panels and 2-pule breakers. No 120 V in that service, so not suitable
for the house.

The last form is center-grounded delta. It gives you both a 3-phase
service, as well as one phase that is grounded at the center-tap. So,
those two hots and neutral look exactly like single-phase home service.
There is a third leg to provide the 3rd phase.

IF!! you can get your electric utility to provide this service, it
probably is the best choice, as you get real 240 V single phase
service PLUS 3-phase with only 5 wires (3 phases, neutral and ground).

Jon

That last one is also known as "wild leg" delta service since the third
phase is not at 120V relative to the ground/neutral, and that third
phase is normally color coded orange to identify it. It wouldn't be a
problem for the house, since that wild leg wouldn't be fed to the house,
but it has been known to cause confusion and blown up 120V stuff in many
installations. Another issue with this type of service is that some
three phase machines may want 120/208V Wye service with it's neutral to
phase voltage at 120V for all phases.

Generally, if you ask the utility for three phase service, you will be
getting 120/208V Wye service unless you specifically ask for something
different. Expect a lot of questions if you ask for three phase service
and a lot more if you ask for anything but the common commercial
120/208V Wye service.

As noted, most appliances these days are 208/240V rated since 120/208V
service is very common in apartment buildings. Check everything to be
sure, but you're not likely to find much that isn't ok with 208V.


The 240 volt systems were designed to save the power company from
installing an extra pole transformer for 240 volt single phase service.

With 208 single phase two pole transformers were needed, and if three
phase were required you needed to install three transformers to obtain
the star or wye configuration. By using the center-tapped transformer
neutral transformer it eliminated a second transformer. If three phase
was required it was necessary to add only one more transformer rather
than two, except when higher power rating were required and a third
transformer is used. That was the difference between open leg delta and
a full delta secondary. A lot of people are confused by seeing only two
high voltage primary wires and getting fed with three phase into their
building but that is very common.


John

Guys, thanks for the discussion on types of three phase. Bit more to
this than I thought. he's talked with the power company and will get
FAR lower install cost if he provides and maintains the transformer.
We're, of course, looking for a used one. With all the different
primary voltages out there and now all the flavors of three phase,
this looks like a tuff task.

Karl


Karl,

Search for pole transformers. If its only the installation cost that is
different I would go for the extra buck and let the power company own
the transformer. If you happen to have one blow from lightning or some
other problem it will be a lot faster if they come and replace it rather
than you searching for a replacement. Also wait till you check on some
of the prices of those pole pigs. Unless you are going to draw a lot of
power you can run open delta with one 240 center tapped grounded and one
240 single phase unit. You only need two legs of the delta to get the
three phase but you get a little less regulation and can only pull the
wattage of the two transformers. Most smaller shops on three phase only
get two pigs on the pole.

John

He's probably looking for a pad mount transformer, not a pole pig.