Harold and Susan Vordos wrote:

"Pete C." wrote in message
...
Harold and Susan Vordos wrote:
snip-----
Huh? You always (unless you've got a 100yr old system) have a ground for
your building system, so once you reach your building distribution you
have a minimum of four wires for a strictly delta system, A, B & C
phases and ground. A Wye system will have five, A, B & C phases, neutral
and ground. The "Wild leg" delta system would also have five wires.

That's what I've been talking about, a wild leg system. That's what I have.
The wild leg measures 208 volts to ground, or neutral.

Your "wild leg" delta system is not very popular these days since most
three phase services are provided by three phase pad mount transformers
so the potential cost savings from using two smaller and one larger
single phase transformers to service the load doesn't exist. The "wild
leg" is also a potential safety issue to people and equipment which is
why the NEC requires the orange color coding and placement in the middle
position of the panelboard.

Yep! That's what I have, the wild leg as the B phase, and it's orange.
One difference-----I have three transformers on the pole in my yard, all the
same size. They are not pad mounted.

That's how everything used to be and I believe both the wild leg and
open delta configurations were primarily used as a way to save
transformer costs.


Ground is not established by the center tap on one transformer, that is
a neutral of sorts. Ground is always established by the ground rod(s)
for your service. The ground and the neutral are always bonded together
at the service entrance panel and never at any sub panels.

Yeah, and thanks for correcting me. I fully meant neutral, but my fingers
got away from me. i hae a basic understanding of the difference between a
ground, and a neutral.

My panel (Square D) provides for a neutral, and I have it. I have a true 5
wire system, run to each individual box in the shop.

Most panels these days are fairly modular and provide bolt in options of
neutral and ground bars.



Again, wrong. It *is* a delta system. He's talking about 240 volts,
not
208. As far as I know, single phase service to the typical house is
just
one leg of a three phase delta system. Isn't that how it comes from
the
power plants, the primary service? How it's delivered to the customer
depends on the transformers that feed them.

Ok, the "wild leg" configuration is technically a delta configuration.
It is however more often referred to with various derogatory terms due
to it's disadvantages.

While older distribution was often fed in a delta configuration, that is
being phased out for safety reasons.

That's an interesting comment. When I discussed three phase service with
PUD, our provider, I was advised that our area, which is relatively remote,
was in bad need of an update, that they were going to provide the second leg
of the three phase service to lighten the load on the single leg, which is,
as I recall, something like 14,000 volts. I was told if I would pay for
the third leg, it would be installed simultaneously, saving me considerable
money, which it did. It dropped the cost from my original inquiry many
years ago from $30,000 to just over $18,000. The point being that,
while it's not necessarily a popular service, they had no problems providing
it to my specs. I was required to provide a large CT can, naturally.

Much of the grid in this country is badly in need of an update
unfortunately. Between cheap utilities not wanting to invest in plant
upgrades and wing nut eco freaks the grid has been festering and
decaying while the load just keeps getting larger.

Oddly enough the grid and service here in fairly rural North Texas is
pretty good. They seem to prefer using individual transformers for each
house or two instead of a secondary bus on the poles with a dozen homes
off of one transformer. My neighbor and I share a 50kva unit on the pole
between us.


When the distribution transformers are fed in a delta configuration, in
the event that there is a circuit loss on one of the phases feeding the
transformer due to a cable break of a fuse blow, the line remains hot
due to power feeding from the other phase through the delta wired
transformer(s) and back down the "disconnected" phase.

Which likely explains the crazy voltages I found when returning from
vacation many years ago when we resided in Utah. Our entire house was wired
with 3 phase, and one of the lines connected to a transformer worked loose,
enough to lose a proper connection. We lost a few things from crazy
voltages. Our refrigerator had been out of service for a long time,
spoiling everything inside.

Similarly bad things happen if you loose the neutral on a typical
120/240 residential service.


A Wye connected transformer does not present this risk since only one
leg of the transformer winding is ties to a hot line with the other at
neutral / ground potential.

But yields only 208 volts. A good friend moved from one shop to another,
the second serviced by a Y service. His CNC machines didn't like that one
bit. Regardless of the fact that machine tools should have motors that
can run on either voltage, I very much prefer to have the higher voltage,
regardless of the inconvenience of losing the B phase for 120V service.
I've managed to work around that very nicely in all situations.

Nope, a Wye connected transformer yields whatever you spec it to yield,
208/120 is just the most popular for light commercial use, if you need
more power you get 480/277 Wye. Of course if you get the 480/277 then
you also need a transformer to give you 208/120 as well.

As for the CNC machines, back when I worked on them I seem to recall
every one I worked on could be wired for a pretty wide range of input
voltages. They also have the small buck/boost autotransformers you can
use on the few machines that truly can't be restrapped for 208.

It would certainly be my preference to use a few autotransformers on one
or two problem machines rather than go with a wild leg system.



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.

Read above. Unless one has 208 volt motors, they tend to run hotter than
necessary if 240 volt motors are run on 208. I don't consider that an
advantage.

Most machines I've seen can accommodate a wide input voltage range, for
the few machines that can't you use the small inexpensive buck/boost
autotransformers.


I consider there to be considerable disadvantages to a system with a
"wild" leg. You have no way to even come close to balancing your single
phase loads on the three phase feed and you have the "wild" leg which
can cause safety issues and/or equipment damage if people are not paying
attention. From what I recall this configuration was primarily used to
cut transformer costs when serviced from three single phase transformers
and not for any technical advantage.

Pete C.

I can't argue with your thoughts, but I'm very comfortable with delta
service, the only three phase I've used for more than 36 years, although my
first service was an open delta. You know what they say about an old
dog. PUD wasn't nearly as concerned about my load balance as you appear to
be, given the fact that they are the ones that wired my two panels, from the
pole to the CT can and meter base (one for three phase, the other for single
phase, which serves both the shop and house, a 375 amp unit). They were
more than aware that I was using the delta service in both capacities.

The utilities aren't that concerned with balance since they can just
switch a few residential streets between phases to balance things. I
just like my power system to be balanced, since that seems to be the
only place in my life where I have any hope of achieving balance. Of
course, not running any large business, I'm still stuck with my rotary
phase converter.

Pete C.