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Default Getting 120v Single Phase from 3 Phase

Can you get 120v single phase by picking off one line of 240v 3 phase
as long as you have a neutral to carry the current back to the box?
Thanks, Steve

  #3   Report Post  
Harold and Susan Vordos
 
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wrote in message
oups.com...
Can you get 120v single phase by picking off one line of 240v 3 phase
as long as you have a neutral to carry the current back to the box?
Thanks, Steve


Yes, but be careful if you have 3 phase delta.. The high leg to ground (B
phase if I'm not mistaken) yields 208 volts, not 120.

Harold


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Jon Elson
 
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wrote:
Can you get 120v single phase by picking off one line of 240v 3 phase
as long as you have a neutral to carry the current back to the box?
Thanks, Steve


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?

Jon

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bw
 
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wrote in message
oups.com...
Can you get 120v single phase by picking off one line of 240v 3 phase
as long as you have a neutral to carry the current back to the box?
Thanks, Steve


Yes, but depending on your load requirement, get an office building
electrician to wire it. The entire USA gets 120 volt single phase from 3
phase sources.


  #8   Report Post  
Pete C.
 
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Harold and Susan Vordos wrote:

"DoN. Nichols" wrote in message
...
In article .com,
wrote:
Can you get 120v single phase by picking off one line of 240v 3 phase
as long as you have a neutral to carry the current back to the box?


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.


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.


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
neutral.



And many are delta which *has* no neutral. All may be floating.


In this case, he's already suggested that there would be a neutral, so it
would be a 5 wire system.


Known as Wye.



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.


I believe this is often referred to as the "wild" leg.


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.


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.

Pete C.
  #9   Report Post  
Robert Swinney
 
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BW sez:

"...The entire USA gets 120 volt single phase from 3 phase sources."

Cute - but not quite right. See John's answer above.

Bob Swinney

"bw" wrote in message
...
wrote in message
oups.com...
Can you get 120v single phase by picking off one line of 240v 3 phase
as long as you have a neutral to carry the current back to the box?
Thanks, Steve


Yes, but depending on your load requirement, get an office building
electrician to wire it.



  #10   Report Post  
Harold and Susan Vordos
 
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"Pete C." wrote in message
...
Harold and Susan Vordos wrote:

"DoN. Nichols" wrote in message
...
In article .com,
wrote:
Can you get 120v single phase by picking off one line of 240v 3 phase
as long as you have a neutral to carry the current back to the box?

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.

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.


If it had a neutral it wasn't a delta service.


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.

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
neutral.



And many are delta which *has* no neutral. All may be floating.


In this case, he's already suggested that there would be a neutral, so

it
would be a 5 wire system.


Known as Wye.


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.



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.


I believe this is often referred to as the "wild" leg.


Agreed.



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.


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.


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.

Harold
..




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Rich The Newsgroup Wacko
 
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On Sat, 11 Jun 2005 01:23:02 -0500, Jon Elson wrote:
wrote:
Can you get 120v single phase by picking off one line of 240v 3 phase
as long as you have a neutral to carry the current back to the box?
Thanks, Steve


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?


No, but it might educate some of the self-proclaimed "engineers" who
claim that the two opposite poles of the 240 center-tapped are "180
degrees out of phase." They are not "out of phase" - they are simply
opposite polarity! It's a significant difference, in the realm of
phasors and imaginary power and stuff.
--
Thanks!
Rich
------
" "Don't come back until you have him", the Tick-Tock Man said quietly,
sincerely, extremely dangerously. They used dogs. They used probes. They
used cardio plate crossoffs. They used teepers. They used bribery. They
used stick tites. They used intimidation. They used torment. They used
torture. They used finks. They used cops. They used search and seizure.
They used fallaron. They used betterment incentives. They used finger
prints. They used the bertillion system. They used cunning. They used
guile. They used treachery. They used Raoul-Mitgong but he wasn't much
help. They used applied physics. They used techniques of criminology. And
what the hell, they caught him." "
-- Harlan Ellison, "Repent, Harlequin, said the Tick-Tock Man"

  #13   Report Post  
Terry Given
 
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Rich The Newsgroup Wacko wrote:
On Sat, 11 Jun 2005 01:23:02 -0500, Jon Elson wrote:

wrote:

Can you get 120v single phase by picking off one line of 240v 3 phase
as long as you have a neutral to carry the current back to the box?
Thanks, Steve


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?



No, but it might educate some of the self-proclaimed "engineers" who
claim that the two opposite poles of the 240 center-tapped are "180
degrees out of phase." They are not "out of phase" - they are simply
opposite polarity! It's a significant difference, in the realm of
phasors and imaginary power and stuff.


sorry Rich, but the two ends of a center-tapped winding *are* 180
degrees out of phase. sin(wt+pi) = -sin(wt).

Cheers
Terry
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John Larkin
 
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On Sat, 11 Jun 2005 23:02:05 GMT, Rich The Newsgroup Wacko
wrote:

No, but it might educate some of the self-proclaimed "engineers" who
claim that the two opposite poles of the 240 center-tapped are "180
degrees out of phase." They are not "out of phase" - they are simply
opposite polarity! It's a significant difference, in the realm of
phasors and imaginary power and stuff.



OK, what would a pair of sine waves look like if they *were* 180
degrees out of phase? How would they be different from a pair of sine
waves that were "simply opposite polarity"? [1]

John [2]

[1] there's a relevant trig identity somewhere, I think

[2] self-proclaimed "engineer" [3]

[3] except for the BSEE, which makes me an
other-proclaimed "engineer"



  #15   Report Post  
Fred Bloggs
 
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On Sat, 11 Jun 2005 01:23:02 -0500, Jon Elson wrote:

wrote:

Can you get 120v single phase by picking off one line of 240v 3 phase
as long as you have a neutral to carry the current back to the box?
Thanks, Steve


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?


Sounds like a lot of blithering crap from one of those 1940's vintage BS
Audel books- absolutely no sense to made of it and zero credibility. And
it's a very rare circumstance to find dedicated 230V or 208V compressors
for A/C- vast majority are dual 208/230.



  #16   Report Post  
Wild Bill
 
Posts: n/a
Default

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
from.

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
this post).

WB
..................

wrote in message
oups.com...
Can you get 120v single phase by picking off one line of 240v 3 phase
as long as you have a neutral to carry the current back to the box?
Thanks, Steve





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  #17   Report Post  
Jon Elson
 
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Fred Bloggs wrote:



On Sat, 11 Jun 2005 01:23:02 -0500, Jon Elson wrote:

wrote:

Can you get 120v single phase by picking off one line of 240v 3 phase
as long as you have a neutral to carry the current back to the box?
Thanks, Steve


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?



Sounds like a lot of blithering crap from one of those 1940's vintage BS
Audel books- absolutely no sense to made of it and zero credibility. And
it's a very rare circumstance to find dedicated 230V or 208V compressors
for A/C- vast majority are dual 208/230.


What I wrote certainly seems to agree with this web site, which I'm
pretty sure has got it all right :
http://www.patchn.com/deltasys.htm

I think this one could be considered pretty authoritative, too :
http://ecatalog.squared.com/catalog/...3%2003-10.html

As for the Air Conditioning, yes most 3-phase small AC are 208/230,
but WINDOW air conditioners generally are NOT. Running a 230 V window
unit on 208 will generally lead to short compressor life, hard starts,
and thermal protector trips.

Jon

  #18   Report Post  
Bob Eldred
 
Posts: n/a
Default


"Rich The Newsgroup Wacko" wrote in message
news
No, but it might educate some of the self-proclaimed "engineers" who
claim that the two opposite poles of the 240 center-tapped are "180
degrees out of phase." They are not "out of phase" - they are simply
opposite polarity! It's a significant difference, in the realm of
phasors and imaginary power and stuff.
--
Thanks!
Rich


"It's a significant difference, in the realm of phasors and imaginary power
and stuff.
Really, do tell? I think mostly "stuff."
Bob


  #19   Report Post  
jk
 
Posts: n/a
Default

"Wild Bill" wrote:


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?



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
time.

jk
  #20   Report Post  
Pete C.
 
Posts: n/a
Default

Harold and Susan Vordos wrote:

"Pete C." wrote in message
...
Harold and Susan Vordos wrote:

"DoN. Nichols" wrote in message
...
In article .com,
wrote:
Can you get 120v single phase by picking off one line of 240v 3 phase
as long as you have a neutral to carry the current back to the box?

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.

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.


If it had a neutral it wasn't a delta service.


Wrong!! One can have a three, four or five wire delta system.


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.


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.


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.


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
neutral.



And many are delta which *has* no neutral. All may be floating.

In this case, he's already suggested that there would be a neutral, so

it
would be a 5 wire system.


Known as Wye.


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.

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.




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.


I believe this is often referred to as the "wild" leg.


Agreed.



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.


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.


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.

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.


  #21   Report Post  
jim rozen
 
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In article , Terry Given says...

sorry Rich, but the two ends of a center-tapped winding *are* 180
degrees out of phase. sin(wt+pi) = -sin(wt).


Referenced from the centertap, of course.

This is something that drives electricians just pure
bonkers. They don't get it.

Jim


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  #22   Report Post  
jim rozen
 
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In article , John Larkin says...

OK, what would a pair of sine waves look like if they *were* 180
degrees out of phase?


Now stop. Yer gonna cause somebody's fuses to blow out...

Jim


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  #23   Report Post  
john
 
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jim rozen wrote:

In article , John Larkin says...


OK, what would a pair of sine waves look like if they *were* 180
degrees out of phase?



Now stop. Yer gonna cause somebody's fuses to blow out...

Jim




HOw about really confusing them with the 30 degree shift going from wye
to delta


John

  #24   Report Post  
George
 
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"Pete C." wrote:

Harold and Susan Vordos wrote:

"Pete C." wrote in message
...
Harold and Susan Vordos wrote:

"DoN. Nichols" wrote in message
...
In article .com,
wrote:
Can you get 120v single phase by picking off one line of 240v 3 phase
as long as you have a neutral to carry the current back to the box?

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.

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.

If it had a neutral it wasn't a delta service.


Wrong!! One can have a three, four or five wire delta system.


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.


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.


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.


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
neutral.



And many are delta which *has* no neutral. All may be floating.

In this case, he's already suggested that there would be a neutral, so

it
would be a 5 wire system.

Known as Wye.


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.

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.




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.

I believe this is often referred to as the "wild" leg.


Agreed.



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.

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.


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.

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
warehouses.

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
leg.

George.

  #25   Report Post  
George
 
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Tom Quackenbush wrote:

jim rozen wrote:
Terry Given says...

sorry Rich, but the two ends of a center-tapped winding *are* 180
degrees out of phase. sin(wt+pi) = -sin(wt).


Referenced from the centertap, of course.

This is something that drives electricians just pure
bonkers. They don't get it.


Uh-huh. I'm not an electrician, but I play one on usenet (also,
Gary seems to be MIA).

What happens when you combine two out of phase signals? What happens
when when you combine the two 120v circuits?


You get 240 single phase service.

Which is great because that's what I need for my air compressor.

George.


  #26   Report Post  
john
 
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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

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.




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.


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
leg.


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.


John

  #27   Report Post  
George
 
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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.

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?

Same question for a corner grounded delta arrangement?

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.




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.


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
leg.


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.


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.


  #28   Report Post  
jim rozen
 
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In article , George says...

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.


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.

Jim


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  #29   Report Post  
john
 
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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
  #30   Report Post  
Harold and Susan Vordos
 
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"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.

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.


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.

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.

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.


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.

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.

Harold




  #31   Report Post  
Pete C.
 
Posts: n/a
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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.
  #32   Report Post  
Jerry Martes
 
Posts: n/a
Default



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



  #33   Report Post  
William
 
Posts: n/a
Default


"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...


  #34   Report Post  
jim rozen
 
Posts: n/a
Default

In article fQire.47092$_o.36229@attbi_s71, William says...

Well there are disadvantages from the 208 voltage, a lot of motors will not
run at 208 with out overheating them.


Buck/boost transformer.

Jim


--
==================================================
please reply to:
JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com
==================================================
  #35   Report Post  
Harold and Susan Vordos
 
Posts: n/a
Default


"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




  #36   Report Post  
Harold and Susan Vordos
 
Posts: n/a
Default


"Pete C." wrote in message
...
Harold and Susan Vordos wrote:

snip----

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.


Regardless of reason, machine shops are typically provided with this
service. The higher voltage is very desirable, and in some cases mandatory.
I question your logic about saving transformer costs if individual machines
would require buck/boost transformers. Between the area required to store
them, and the increased cost of labor for installing them, seems to me it's
a terrible waste of money when it can be dealt with by installing the delta
system instead of the wye.


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.


But you've overlooked the fact that it does *not* yield 240 volts, the
optimum voltage for machine tools. I'm having more than a little trouble
understanding why you feel delta is such a bad deal when it solves all
problems aside from the wild leg issue. I can't think of one small
machine shop that is wired wye------not one. Many of my friends are still
in business in Utah, all of which have the delta service. Could be it's a
regional thing. Dunno.

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.


Or you could use 3 phase delta and ignore buying buck/boost transformers and
their inherent problems. I thought that was an excellent idea.

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.


You keep speaking of these problems, but I've had 3 phase delta systems
since 1967, and aside from the one failure, which would have occurred be it
delta or wye, I've never had any problems. From that I conclude that the
problems, while possibly serious, are highly unlikely to plague the average
person. I'm more than willing to gamble on these ethereal problems than
request wye service and know for damned sure I'm going to face other
problems, which I would. I get the idea you're geared to light commercial,
where wye service is the norm. Machine shops do not use it----for obvious
reasons. Places that have a lighting load that tends to be the largest
power demand is where you find lots of wye service, at least in my
experience.



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.


We've already kicked that around. Why buy more transformers when you can
get the proper voltage?


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.


Yeah, the one that puts out 240 volts---------do you get my drift?

Funny, I get the distinct idea you think I made a mistake by installing the
delta system. You couldn't be more wrong if you tried. It serves my
purpose perfectly, very unlike a wye system.

Harold


  #37   Report Post  
Pete C.
 
Posts: n/a
Default

Harold and Susan Vordos wrote:

"Pete C." wrote in message
...
Harold and Susan Vordos wrote:

snip----

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.


Regardless of reason, machine shops are typically provided with this
service. The higher voltage is very desirable, and in some cases mandatory.
I question your logic about saving transformer costs if individual machines
would require buck/boost transformers. Between the area required to store
them, and the increased cost of labor for installing them, seems to me it's
a terrible waste of money when it can be dealt with by installing the delta
system instead of the wye.


The transformer cost savings was for the large oil filled cans on the
pole, by using only two for open delta, or two smaller and one larger
for the unbalanced wild leg.

The buck/boost autotransformers are quite small and inexpensive. They
are dry type autotransformers, not full isolating transformers with
multiple windings so they are much smaller than you would expect for
their capacity. The KVA size required for the autotransformer is not the
full KVA of the load. The sizes you would need for an average machine
are about shoe box size and around $150 new.

http://www1.mscdirect.com/CGI/NNPDFF...PARTPG=NNLMK32

The other point is that many machines have appropriate taps and
connections on their motors and/or internal transformers and would not
require the buck/boost.



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.


But you've overlooked the fact that it does *not* yield 240 volts, the
optimum voltage for machine tools. I'm having more than a little trouble
understanding why you feel delta is such a bad deal when it solves all
problems aside from the wild leg issue. I can't think of one small
machine shop that is wired wye------not one. Many of my friends are still
in business in Utah, all of which have the delta service. Could be it's a
regional thing. Dunno.


How is 240v "optimum" for machine tools? A lot of machines larger than
bench top size can be strapped for operation on 480v input as well. When
I did CNC service, I don't recall seeing a single machine that didn't
have a 480v input option.

I would consider "optimum" voltage for a machine to be any voltage that
it can be strapped for. If it was designed with those taps then it
should operate just as well on any of them.

The "optimum" voltage that you would want to use based on external
factors would be one of the higher voltage options based on smaller
required wire gauge, reduced voltage drop, etc. From that standpoint
208v and 240v are essentially equal.

If a machine has taps for both 208v and 240v then there is no advantage
or disadvantage to either, only the convenience of what you have
available. If there are a sufficient number of machines that can take
480v to fill a decent portion of a 480v panel then that is an even
better choice.

I didn't say that delta was bad, I said that delta with a wild leg was
bad, they are two different things. Take a (pure) delta service for the
three phase and use a proper transformer to provide 208/120 Wye and I'd
be happy. No wild leg anywhere, and you've still got your 240v delta
that you like, as well as the familiar and flexible 208/120. Of course
it would still be preferable to go with the 208/120 Wye to begin with
and save the complexity.

I also didn't say that there were not plenty of shops with the wild leg
service. If it's already in place in a shop and in good condition there
is little reason to change it. I would not use it for a new
installation.


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.


Or you could use 3 phase delta and ignore buying buck/boost transformers and
their inherent problems. I thought that was an excellent idea.


What inherent problems? For the few machines that might require them in
a decent sized shop cost should not be an issue. They are quite small so
space should not be an issue. They are not difficult to wire so
installation should not be an issue.

Many years ago I worked for a mid sized printing company. The building
had 208/120 service, and there was only one machine in the entire
company that required the buck/boost transformers, a press made in
Sweden.


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.


You keep speaking of these problems, but I've had 3 phase delta systems
since 1967, and aside from the one failure, which would have occurred be it
delta or wye, I've never had any problems. From that I conclude that the
problems, while possibly serious, are highly unlikely to plague the average
person. I'm more than willing to gamble on these ethereal problems than
request wye service and know for damned sure I'm going to face other
problems, which I would. I get the idea you're geared to light commercial,
where wye service is the norm. Machine shops do not use it----for obvious
reasons. Places that have a lighting load that tends to be the largest
power demand is where you find lots of wye service, at least in my
experience.


Failures due to poor maintenance can and will occur with any power
system. Annual IR camera inspections really are cheap insurance since
they can usually spot these problems developing before they can do any
damage.

These days when you can get a handheld IR thermometer for $50 at Sears
you can do the inspections yourself and save even more money. Granted
it's a little slower than with an IR camera, but not that much slower.
Do a monthly scan, input the data to a spreadsheet and pickup problem
trends even faster.

Wye service is indeed good for buildings with a lot of lighting load,
480/277 is particularly good for that.

The main thing is that you are indicating that there is a big
disadvantage to 208v vs. 240v which I just don't see. I think your
making more of the difference between 208v and 240v than there is
justification for.

The allowable voltage range for your 240/120 3ph delta wild leg service
is from 220v-254v at the service entrance (from a chart referencing ANSI
C84.1-1989). If the service is considered acceptable over a range of 34v
I just don't see a 32V difference between services as significant.

Large motors are built to handle widely varying power and load
conditions, and power supplies for controls either have plenty of tap
adjustment range for older machines, or switching supplies for newer
machines that are happy on anywhere from 98v - 250v. Your motors might
run a few degrees warmer but still well within their specified operating
range and your controls should be perfectly happy as well.



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.


We've already kicked that around. Why buy more transformers when you can
get the proper voltage?


Again, because not many machines would actually require it, and the fact
that your "proper" 240V service is allowed to vary over a 34v range
anyway.

Basically I think the 14% or so difference is of little to no
significance for 95% of the possible machines you might run, and for
those few the fix is easy and inexpensive.



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.


Yeah, the one that puts out 240 volts---------do you get my drift?


Er, no, a couple weeks ago I had 269V! A call to TXU had that fixed in
less than one hour fortunately (good response).

And actually the 240V is some 9% high for the machine, as it's motor is
rated for 220/440.


Funny, I get the distinct idea you think I made a mistake by installing the
delta system. You couldn't be more wrong if you tried. It serves my
purpose perfectly, very unlike a wye system.


I think my main point is that I feel the Wye system would have served
your needs equally well and would have simplified the installation by
avoiding your use of separate panels for your single and three phase
loads to avoid the wild leg issue.

Pete C.
  #38   Report Post  
Don Murray
 
Posts: n/a
Default



Pete C. wrote:


The allowable voltage range for your 240/120 3ph delta wild leg service
is from 220v-254v at the service entrance (from a chart referencing ANSI
C84.1-1989). If the service is considered acceptable over a range of 34v
I just don't see a 32V difference between services as significant.

Large motors are built to handle widely varying power and load
conditions, and power supplies for controls either have plenty of tap
adjustment range for older machines, or switching supplies for newer
machines that are happy on anywhere from 98v - 250v. Your motors might
run a few degrees warmer but still well within their specified operating
range and your controls should be perfectly happy as well.


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.


We've already kicked that around. Why buy more transformers when you can
get the proper voltage?



Again, because not many machines would actually require it, and the fact
that your "proper" 240V service is allowed to vary over a 34v range
anyway.


Peter,
Do you think it would be OK to run the 240 motor on 197.6V ? Because
that's what could happen when you hook it up to a 208 service. Most all
power companies have a 5% tolerance on their service voltage. So a 240
service can go from 238 to 252. And a 208 service can go from 197.6 to
218.4. The purpose of a 208 service is to serve buildings with large
lighting loads and small 3-phase loads. There is a lot of commercial 240
3-phase and a lot of houses that have their own 3-phase wells will also
have a grounded center tap delta. I happen to have a 10HP 3-phase pump
with a straight 3-phase service, 3hot wires and no neutral to the pump.
The bank across the street from my house has a 25KVA and 2 10KVA
transformers, in a center tap grounded delta. My house 120/240 single
phase also comes off of this same bank.

Don

  #39   Report Post  
Don Murray
 
Posts: n/a
Default



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.

Don


  #40   Report Post  
Pete C.
 
Posts: n/a
Default

Don Murray wrote:

Pete C. wrote:


The allowable voltage range for your 240/120 3ph delta wild leg service
is from 220v-254v at the service entrance (from a chart referencing ANSI
C84.1-1989). If the service is considered acceptable over a range of 34v
I just don't see a 32V difference between services as significant.

Large motors are built to handle widely varying power and load
conditions, and power supplies for controls either have plenty of tap
adjustment range for older machines, or switching supplies for newer
machines that are happy on anywhere from 98v - 250v. Your motors might
run a few degrees warmer but still well within their specified operating
range and your controls should be perfectly happy as well.


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.

We've already kicked that around. Why buy more transformers when you can
get the proper voltage?



Again, because not many machines would actually require it, and the fact
that your "proper" 240V service is allowed to vary over a 34v range
anyway.


Peter,
Do you think it would be OK to run the 240 motor on 197.6V ? Because
that's what could happen when you hook it up to a 208 service. Most all
power companies have a 5% tolerance on their service voltage. So a 240
service can go from 238 to 252.


I think something is wrong with your math there or you have a typo. At a
+/- 5% tolerance the nominal 240V service would range from 228V to 252V.
According to that ANSI spec 220V to 254V is acceptable.

And a 208 service can go from 197.6 to
218.4. The purpose of a 208 service is to serve buildings with large
lighting loads and small 3-phase loads. There is a lot of commercial 240
3-phase and a lot of houses that have their own 3-phase wells will also
have a grounded center tap delta. I happen to have a 10HP 3-phase pump
with a straight 3-phase service, 3hot wires and no neutral to the pump.
The bank across the street from my house has a 25KVA and 2 10KVA
transformers, in a center tap grounded delta. My house 120/240 single
phase also comes off of this same bank.


The different sized transformers is what I referenced about cost savings
for the wild leg configuration, with the 10KVA transformers costing less
than the 25KVA transformer.

A quick look on the Grainger site doesn't even find any 240V 3ph motors
at all. They all seem to be spec'ed for 208-220/440 or 208-230/460. The
Baldor site is also devoid of any 240V rated three phase motors, they
list motors with 208-230 range and some at 220V or 230V.

The Baldor spec's indicate for a 2HP motor the FLA difference between
208V and 230V is .5A (12 vs. 11.5). If the entire current difference was
dissipated as heat, which it is not, that's a whopping 104W extra to
dissipate from the surface of a beefy 60# motor - hardly a big deal in
just about any application.

So once again I think that there are very few machines that would
actually have any adverse effects from running on a 208V service.

An existing building with wild leg delta service that was in good
condition would be fine with me. For a new installation I would not
spec. a wild leg delta service.

Pete C.
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