Not quite. The voltage won't be right for pure three phase. I
think that with Wye connections, you will have something closer to 104V.
And many are delta which *has* no neutral. All may be floating.
But a frequent variation has one of the three sides center
tapped (the way the standard residential feed is supplied, 240V center
tapped with the center tap grounded and neutral connected to that.)
The breaker boxes for this have three buses, but only two of
every three positions can be used for 120V single-phase breakers. The
third phase is *way* too high.
However -- from *any* reasonable 240V 3 phase, you can tie two
of the three phases to the primary of a 240-120V step-down transformer,
and power your equipment from that.
I'm at a loss to understand that, DoN. Care to elaborate? I have wired
three places with delta service, two of which used either the A and C phase
and the neutral for 120V. All of it was done to code. The third place
has a single phase panel along with the 3 phase, both of which are fed from
the same taps from the transformers.
In this case, he's already suggested that there would be a neutral, so it
would be a 5 wire system.
As stated above, I got around that problem in my current shop by having two
panels, one strictly 3 phase, so none of the positions are lost.
Only in a special circumstance, which is a 4-wire, center-tap grounded
delta service. This has one 240 V L-L circuit with a center tap, just
like everybody's home service. Then, it has another transformer that
develops the 3rd phase. In this system, there are only TWO of the three
hot wires that will give 120 V to neutral. (The third will give ~207 V,
so you will definitely be able to tell which is which with a meter.)
This service is pretty rare, at least around where I've lived.
Corner-grounded delta is more common, but you can't get 120 V
directly from that. You need a 240 - 120 step-down transformer.
Corner-grounded delta is most obvious because 2-pole circuit breakers
and disconnects are used. The 3-phase wires are hot, hot and neutral,
and you can wire a 3-phase motor up to those 3 wires. (These are also
labeled hot (A), neutral (B), and hot (C) phases, and therefore
sometimes called grounded B phase.)
If you have 208 V WYE service (sometimes called star) you have three
120 V circuits, from any line to neutral. But, in this system,
you can't get 240 V, without a transformer. Like, the building
I work in, has 208 V Wye for the office section, and we have little
autotransformers to step 208 up to 240 for the window air conditioners.
If you try this on a true 240 V Wye system, which has a neutral, you
will get a rather high voltage of about 138 V. But, 240 V Wye
is pretty rare. If you try this on a real delta system, you might kill
all the lights in the building, as it may trip the ground fault
protection. But, then, a true delta system doesn't have a NEUTRAL,
although sometimes telling the difference between a neutral and a safety
ground can be difficult. Delta transformers have a balancing
transformer in them that makes it look like they are referenced to a
neutral, but if you draw any current from line to neutral that
unbalances it, the transformer should shut down. This normally wouldn't
apply to open delta and corner or center-tap grounded deltas, as they
are expected to feed unbalanced loads.
Is that more than you wanted to know?
If it had a neutral it wasn't a delta service.
The 104V mentioned was a typo, it's really 138V and change. Square root
of three thing for three phase power. 240V Wye service will give you
138V phase to neutral and 208V Wye service will give you 120V phase to
Known as Wye.
I believe this is often referred to as the "wild" leg.
There are / were a lot of strange variations on three phase power, but
most anything new is going to be 208V Wye service. Larger industrial
stuff will get 480V.
Wrong!! One can have a three, four or five wire delta system.
I have a 5 wire system, and it *is* a delta system. It is not a wye, which
does not have the wild leg. Mine does have. Ground is established by
tapping the center of one coil, which results in the longer path to ground
from the other two coils. 208 volts from phase to ground. It's not
conjecture, it's measured.
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.
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.
Nuttin' personal, but I'm always amused by the perceptions (or just commonly
used expressions) that power or voltage comes out one terminal and goes back
to the other one.
I usually have nothing better to do than to ask.. then where does it go?
In the context of power generation and distribution, does it go back to the
generation source? What do they do with all the power they receive back?
In a battery context, does the battery determine that the user has gotten
their money's worth, and stop giving the user more voltage? Why did it go
dead if there is power coming back into the other terminal?
Does it become saturated wih negativity?
Is the battery recycling program about using the unused power in dead
batteries to make new batteries?
Can folks visualize that the power is expended at the load? Transformed into
light, mechanical energy, heat, and simply dissipated at the electrical
load. Maybe it's been transferred into food to make it hot?
My food is too hot, can I return some of this wasted energy to the power
company (and get a credit?).
Maybe visualization is too complex, but generally, there is always heat
present and that can be felt or measured.
Ground is always zero, right? Depends on where you're coming from, pal. So I
guess you're saying ground is never zero? Definite maybe.
What's neutral? Switzerland, I think. Again, depends on where you're coming
Prototypes of the generator powered by free radon should be available in the
first quarter of 2007.
Be sure to check to see if you have radon. (which is the only useful info in
It is quite simple! :)
Since it is coming in to the OTHER terminal, it is coming back a
"UNPOWER". As the battery fills up with unpower, pretty soon it
balances out the power that is left. Then pffft nothing.
But un power is a little more volatile, and so it evaporates just a
little faster. This is why if you let the battery sit for a little
while, you can get just a little more oomps out of it for a short
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.
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.
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.
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.
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.
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.
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.
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.
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.
If I had Wye or corner grounded delta service then I would have to
give up one of those conditions or purchase another transformer.
By the way: center tapped delta service is very common here in the
Chicago area. Wye service is strictly used in office buildings and
As a side note: I have a suspicion that Commonwealth Edison balances
the overall service in an industrial park by locally grounding the
center of alternate coils. IOW: that wire that comes into my building
and that I call the wild leg, is not the same as my neighbor's wild
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
It is good for the electrical company when there is a mixed use of
single and light three phase users. They save a transformer when three
phase is required.
All utility companies alternate on the hookup of the primary to the
three phase high voltage lines, the ones on the extreme top of the pole
with the big insulators.
you neighbor may be on a different pole transformer. IF he is then his
phasing is different than yours.
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.
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
Same question for a corner grounded delta arrangement?
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
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
No, it runs at full power. Motors however draw more current
and run hotter. The typical approach (inexpensive) is to
simply put a buck/boost transformer at each item that really
requires 240 volts.
Thats one of the nice things about using 240 volts. Overvoltage is
usually less harmful than undervoltage
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
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.
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.
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.
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.
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.
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.
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.
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.
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.
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
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.