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Jack Fisher
 
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Default 3 phase 240VAC to 120 VAC single phase?

Ok, I've got the opposite problem that most of the people here have
with regards to AC power. I've got a 400 amp 3 phase service in the
back half of the building I moved into a few months ago. I'm going to
be leasing out this portion of the building and the electric company
bills me separately for this panel.

What I want to be able to do is have this panel supply the power for
this portion of the building so I can have an accurate record of the
electrical use for the tenant. I have another 200 amp 3 phase service
and 200 amp single phase service for the other portion of the building
that I'm using for the shop (RCM related) and living space.

My question is how can I tap single phase 110VAC off this panel for
regular power for this portion of the building? I've checked the
panel in question with a VOM and I get 240 VAC to ground off of each
of the two hot leads coming in and the neutral and ground are both
connect to the same bus inside the panel. Checking the between both
hot leads I also get 240VAC. What am I going to have to do or install
to meet my needs?

Thanks in advanced for the help. I know some of you guys know what I
need to do.

Jack Fisher
  #2   Report Post  
Bob Swinney
 
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Default 3 phase 240VAC to 120 VAC single phase?

Jack,
Maybe, it's me and I've only had coffee #2 this morning ... but your
question reads as if you want to somehow meter 3-phase service and
single-phase service for both areas from your location. It would seem the
logical solution would be to have the leased area billing put in your
tenant's name. Otherwise, combining single-phase and 3-phase service in the
same panel would involve the use of transformer(s). This type of question
would be much better put to your electric utility.
Bob Swinney


"Jack Fisher" wrote in message
om...
Ok, I've got the opposite problem that most of the people here have
with regards to AC power. I've got a 400 amp 3 phase service in the
back half of the building I moved into a few months ago. I'm going to
be leasing out this portion of the building and the electric company
bills me separately for this panel.

What I want to be able to do is have this panel supply the power for
this portion of the building so I can have an accurate record of the
electrical use for the tenant. I have another 200 amp 3 phase service
and 200 amp single phase service for the other portion of the building
that I'm using for the shop (RCM related) and living space.

My question is how can I tap single phase 110VAC off this panel for
regular power for this portion of the building? I've checked the
panel in question with a VOM and I get 240 VAC to ground off of each
of the two hot leads coming in and the neutral and ground are both
connect to the same bus inside the panel. Checking the between both
hot leads I also get 240VAC. What am I going to have to do or install
to meet my needs?

Thanks in advanced for the help. I know some of you guys know what I
need to do.

Jack Fisher



  #3   Report Post  
Gary Coffman
 
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Default 3 phase 240VAC to 120 VAC single phase?

On 10 Jul 2003 05:43:31 -0700, (Jack Fisher) wrote:
My question is how can I tap single phase 110VAC off this panel for
regular power for this portion of the building? I've checked the
panel in question with a VOM and I get 240 VAC to ground off of each
of the two hot leads coming in and the neutral and ground are both
connect to the same bus inside the panel. Checking the between both
hot leads I also get 240VAC. What am I going to have to do or install
to meet my needs?


What you have is corner grounded delta. What you're calling "neutral"
isn't actually neutral. It is one of the 3 hot legs, which happens to be tied
to ground. (Doesn't matter to the 3 ph, voltages to ground for a 3 ph delta
are abritrary anyway, zero is as good a value as any.) This is a common
way to wire industrial power. You can get 3 ph 240, or single phase 240
from this system. But you can't get 120 without another transformer.

The only way you're going to get 120 out of this is with a stepdown
isolation transformer with its primary across one pair of legs, and its
secondary feeding a separate 120 volt panel. Pick one of the secondary
leads, call it neutral, and ground it in the 120 volt panel. Call the other
lead hot, and feed it to your 120 volt breakers.

You probably should check with your power company to see if they'll
change your service over to 4 wire delta with one phase centertapped.
That way you can get 120 between neutral (actual neutral now) and
either one of two of the three hot legs. The third leg, called the high
or wild leg in this configuration, will read more than 240 to ground.
Again this doesn't matter to the 3 ph, but you don't want to use it
with the 1 ph wiring. This type of service is commonly used for
small office buildings where the loads are primarily 1 ph, but with
some 3 ph required for air conditioning, elevators, etc.

They'll probably want to charge you to make this change since
it'll require setting a new transformer and changing your entrance
drop (you'll also have to change your entrance panel). But you're
going to have to buy a transformer anyway, and a separate 120
volt panel, so at least you'll see which would be cheaper. (I'm
betting the latter in most cases.)

Another option would be to order a separate 240 single phase
drop. That would be the ordinary residential type setup using
3 wires, hot, neutral, and hot. You could then install a panel for
this and wire it like a house, giving single phase 240 between
the hots, or single phase 120 from either hot to neutral. The
big advantage of this over the other setup is you minimize the
surges you'll get on the 120 volt circuits due to large 3 ph loads
being switched on or off.

Note you probably don't want to change to 4 wire wye service.
That would give you 120 volts to neutral from any leg, but the
leg to leg 3 ph voltage would drop to 208. That would require
rewiring all your 3 ph motors for 208 instead of 240. This was
found a lot in older installations, but most power companies
don't want to provide this any more.

In new work, the power company is going to want to supply you
with 480 wye. That gives you 480 3 ph, and 277 1 ph (for lighting)
from any leg to neutral. Now you need to supply stepdown
transformers to get 240 3 ph, or 240 1 ph, or 120 1 ph. The
advantage of this in a large building is that you can use 480
wiring to each subpanel, and site stepdown transformers at
each subpanel to give you the 240 or 120 volts your applications
actually need. This can save a bundle on distribution wiring in a
large building, easily offsetting the cost of the extra transformers.
But it is a pain in the ass for a smaller building.

Obviously, whichever way you choose (and whichever way your
power company will let you choose), you're going to need the
services of an industrial electrician to wire it all up. He, and the
building inspector, are going to be the final authorities on what
you can do in your jurisdiction.

Gary

  #4   Report Post  
Don Murray
 
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Default 3 phase 240VAC to 120 VAC single phase?



Gary Coffman wrote:
The third leg, called the high

or wild leg in this configuration, will read more than 240 to ground.


Not so. The high leg or wild leg, also called the power leg, will be 208 volts to
ground.
I have some pictures of transformer connections on a web page. Scroll to the
bottom of the page to see them.

http://murrayranch.com/Electricity.htm

. This was
found a lot in older installations, but most power companies
don't want to provide this any more.
Gary


Not so, again. This is still widely in use. At the power company I work for we
install a lot of these, many in strip malls, supermarkets and small office
buildings. Anyplace that has a large 120 load, and need some 3-phase for
refrigeration and air conditioning.

Don

  #5   Report Post  
Peter H.
 
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Default 3 phase 240VAC to 120 VAC single phase?



Not so.


Semantics.

The "third leg", often called the "high leg" or "red leg" really should be
called the "orange leg" as all new work is required to indicate this leg with
orange wire (small gauges) or orange tape (large gauges).

No single-phase loads are permitted on such a leg.



  #6   Report Post  
Gary Coffman
 
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Default 3 phase 240VAC to 120 VAC single phase?

On Fri, 11 Jul 2003 01:50:43 GMT, Don Murray wrote:
Gary Coffman wrote:
The third leg, called the high

or wild leg in this configuration, will read more than 240 to ground.


Not so. The high leg or wild leg, also called the power leg, will be 208 volts to
ground.
I have some pictures of transformer connections on a web page. Scroll to the
bottom of the page to see them.

http://murrayranch.com/Electricity.htm


You're right, sqrt(240^2 - 120^2) = 207.846 volts.

. This was
found a lot in older installations, but most power companies
don't want to provide this any more.
Gary


Not so, again. This is still widely in use. At the power company I work for we
install a lot of these, many in strip malls, supermarkets and small office
buildings. Anyplace that has a large 120 load, and need some 3-phase for
refrigeration and air conditioning.


Nope, you took that one out of a different context. I'm talking about 208 delta
there. Your power company may still support it for new work, but none of the
ones I know will (though they continue to support it in old work). They want
to supply 480 wye instead. It saves them money via smaller cheaper transformers.
In a stretched out facility it saves you money too, in reduced copper costs.

Gary


  #7   Report Post  
Peter H.
 
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Default 3 phase 240VAC to 120 VAC single phase?



I'm talking about 208 delta there. Your power company may still support it for
new work, but none of the ones I know will (though they continue to support it
in old work). They want to supply 480 wye instead.


120/208Y is still the bulk of the new Wye installations, far outpacing
277/480Y.

Installations usually follow this sequence (as a function of intended usage and
total premises volume):

1) 120/240 center-tap grounded Delta (mixed use, small to medium volume),

2) 120/208 Wye (mostly power, small to medium volume), and

3) 277/480 Wye (industrial, large volume).

In (3), a customer-owned "dry type" transformer or transformers is (are)
required to provide 120 single-phase, 120/240 single phase or 120/208 Wye
and/or 240 Delta three-phase.

  #8   Report Post  
Don Murray
 
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Default 3 phase 240VAC to 120 VAC single phase?



Gary Coffman wrote:


Nope, you took that one out of a different context. I'm talking about 208 delta
there. Your power company may still support it for new work, but none of the
ones I know will (though they continue to support it in old work). They want
to supply 480 wye instead. It saves them money via smaller cheaper transformers.
In a stretched out facility it saves you money too, in reduced copper costs.

Gary


Gary,

I don't think I took anything out of context, I am going to cut and paste the
paragraph from your original post so you can see why I thought you were talking about
208 wye.

"Note you probably don't want to change to 4 wire wye service.
That would give you 120 volts to neutral from any leg, but the
leg to leg 3 ph voltage would drop to 208. That would require
rewiring all your 3 ph motors for 208 instead of 240. This was
found a lot in older installations, but most power companies
don't want to provide this any more."

I've never heard of a 208 delta, other than the high leg on a 240 bank.

The determining factor in whether you will get a wye or delta secondary is the voltage
of the service. You can see the wye secondary transformer connections on my web page
have the secondary coils paralleled. What determines whether the high side is delta or
wye is the actual primary voltage of the line and the nameplate rating of the
transformer. Where I work, we have a lot of 12KV primary and a 20.8KV primary that we
use the same transformers on. The company stocks a lot of 12KV 120/240 transformers.
So if you are going to hang a bank to serve a 208V 3-phase service in the 20.8KV you
pop the lid off the transformers, parallel the secondary coils, and hang a wye-wye
bank. If you wanted a 240V 3-phase bank in the 20.8KV, it would be a wye-delta. If you
are hanging these 12KV transformers in the 12KV primary, it would be a delta
high-side. And again the secondary configuration would be determined by the secondary
voltage you want, 120-208V requires you to parallel the secondary coils and wye the
secondary side. 120-240V would be delta secondary.

The 20.8KV system is a common neutral system. That is the neutral carried in the
secondary position is shared by the primary and secondary, and is a metallic return to
the substation.

Don

  #10   Report Post  
Peter H.
 
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Default 3 phase 240VAC to 120 VAC single phase?



But then the building is supplied with two 13.8 kV feeders. I think we do our
own on-site transformations from there on down.


Most likely.

While at my former employer we NEVER allowed one of our customers to connect to
our transmission systems (115 kV ac through 500 kW ac, and 800/1,000 kV dc), we
DID allow our large industrial customers/municipal partners to connect to our
subtransmission systems (34.5 kV, most, and 69 kV, a few).

Note that MOST (but not all) system voltages are multiples of 115 ...

13.8 kV = 120 X

34.5 kV = 300 X

69 kV = 600 X

115 kV = 1,000 X

138 kV = 1,200 X

230 kV = 2,000 X

287.5 kV = 2,500 X (Hoover to L.A., Circuits 1 and 2, e.g., in L.A.'s system)

345 kV = 3,000 X (not used in L.A.'s system, but used within the "Western
System", APS, e.g.)

But ...

500 kV / 115 = 4347.8261 (Hoover to L.A., Circuit 3, e.g. and the "Western
System" ac Intertie, e.g.), and

765 kV / 115 = 6652.1739 ("Eastern System" ac Intertie, e.g.).

Oh, well.




  #11   Report Post  
Gary Coffman
 
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Default 3 phase 240VAC to 120 VAC single phase?

On Sun, 13 Jul 2003 18:42:32 GMT, Don Murray wrote:
Gary Coffman wrote:


Nope, you took that one out of a different context. I'm talking about 208 delta
there. Your power company may still support it for new work, but none of the
ones I know will (though they continue to support it in old work). They want
to supply 480 wye instead. It saves them money via smaller cheaper transformers.
In a stretched out facility it saves you money too, in reduced copper costs.

Gary


Gary,

I don't think I took anything out of context, I am going to cut and paste the
paragraph from your original post so you can see why I thought you were talking about
208 wye.

"Note you probably don't want to change to 4 wire wye service.
That would give you 120 volts to neutral from any leg, but the
leg to leg 3 ph voltage would drop to 208. That would require
rewiring all your 3 ph motors for 208 instead of 240. This was
found a lot in older installations, but most power companies
don't want to provide this any more."

I've never heard of a 208 delta, other than the high leg on a 240 bank.


I misspoke (miswrote), I meant 208 wye.

Gary

  #13   Report Post  
Don Murray
 
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Default 3 phase 240VAC to 120 VAC single phase?



"Bruce L. Bergman" wrote:

On Mon, 14 Jul 2003 02:08:02 GMT, someone who calls themselves Don
Murray wrote:

I'm surprised noone's asked about the lights you have to scroll past on my web page
to get to the transformer connections. These lights are old series street lights from
what is called an arc circuit. These were fed from a special transformer called an
RO. (regulated output) These usually put out a constant 6.6 amps or a few put out 3.3
amps. The voltage varies by the number of lights. This is done with a movable core on
a counterbalance. A characteristic of an RO transformer is when you open the circuit,
the voltage goes to the maximum, which is slightly above the primary. That's where
the term arc circuit comes from. When a light burns out the RO will go up to 5000V
and burn through the little wafer you see below the mogul base of the lamp. We still
have these in the old part of town in the 4160V area.


http://www.murrayranch.com/Electricity.htm

Don


Just had a chance to go look - oh, /that's/ what they are... (Ever
heard of photo captions?) What was the logic behind a series circuit,
anything besides saving on wire with just one wire in a big ring?


I don't normally put photo captions on that page, as the pictures don't usually stay up
very long. I just post them for a specific discussion, or to show a friend.
I can't speak to the logic of it, they were designed before my time. I've only been in the
business 31 years, some of that stuff is nearly a hundred years old.


I suppose the wafer burns through and reconnects the circuit, and
the base for the pull-lout socket has bypass contacts so you can
replace the lamp and wafer. Hot-Work Gloves Required...


That's all correct. Some other working rules on an arc circuit are you never work it hot,
but you always work it like it's hot, as it can be wrapped in the 4KV and still be
working. You never ground it, and you never open it. You put a shunt across a light when
you are working on it.




You want odd, I know of a trolley system where they've still got a
fully operable GE 2400VAC to 600VDC converter station running and in
service, complete with 6-phase transformer and a rotary converter, and
dump relays in case it has to scram on an overload and open the output
contactor without frying the converter windings.


That sounds interesting, I'd like to see pictures of it.



Stand there and watch the drum controller go through the automatic
start-up and shut-down sequences, and the damned thing looks like a
100% Rube Goldberg design - but it still works ~100 years later...

-- Bruce --


Don

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Bruce L. Bergman
 
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Default 3 phase 240VAC to 120 VAC single phase?

On Wed, 16 Jul 2003 01:31:59 GMT, someone who calls themselves Don
Murray wrote:
"Bruce L. Bergman" wrote:
On Mon, 14 Jul 2003 02:08:02 GMT, someone who calls themselves Don
Murray wrote:


I'm surprised noone's asked about the lights you have to scroll past on my web page
to get to the transformer connections. These lights are old series street lights from
what is called an arc circuit. These were fed from a special transformer called an
RO. (regulated output) These usually put out a constant 6.6 amps or a few put out 3.3
amps. The voltage varies by the number of lights. This is done with a movable core on
a counterbalance. A characteristic of an RO transformer is when you open the circuit,
the voltage goes to the maximum, which is slightly above the primary. That's where
the term arc circuit comes from. When a light burns out the RO will go up to 5000V
and burn through the little wafer you see below the mogul base of the lamp. We still
have these in the old part of town in the 4160V area.
http://www.murrayranch.com/Electricity.htm


Just had a chance to go look - oh, /that's/ what they are... (Ever
heard of photo captions?) What was the logic behind a series circuit,
anything besides saving on wire with just one wire in a big ring?


I don't normally put photo captions on that page, as the pictures don't usually stay up
very long. I just post them for a specific discussion, or to show a friend.
I can't speak to the logic of it, they were designed before my time. I've only been in the
business 31 years, some of that stuff is nearly a hundred years old.

I suppose the wafer burns through and reconnects the circuit, and
the base for the pull-out socket has bypass contacts so you can
replace the lamp and wafer. Hot-Work Gloves Required...


That's all correct. Some other working rules on an arc circuit are you never work it hot,
but you always work it like it's hot, as it can be wrapped in the 4KV and still be
working. You never ground it, and you never open it. You put a shunt across a light when
you are working on it.


Looks like they use the same type system for the series-circuit HPS
streetlights in the Valley, with the big pole-mount RO transformers...
I've seen the whole string cycle before, probably from one lamp that's
at end-of-life and blows out, and knocks the whole string down...

All in all, I'll go for regular 120/240/277V feed Cobra-heads, thank
you. Easy to troubleshoot and repair, or swap out. And you don't
dump the whole circuit because of one bad lamp.

You want odd, I know of a trolley system where they've still got a
fully operable GE 2400VAC to 600VDC converter station running and in
service, complete with 6-phase transformer and a rotary converter, and
dump relays in case it has to scram on an overload and open the output
contactor without frying the converter windings.


That sounds interesting, I'd like to see pictures of it.


Orange Empire Railway Museum, Perris CA. www.oerm.org I'll have to
see if I have pictures - someone should film it doing a
startup/shutdown cycle for historical purposes. Open contactors and
arc chutes, brush lifter motors...

The best part is the little worm-and-ball 'rotor wiggler' that moves
the rotor in the sleeve bearings to keep the brushes from taking a set
on the commutator, as it coasts down you can hear the ball coming off
one end and going 'plink' as it goes back to the other end of the worm
for another cycle...

And it should be good for another 100 years, as the GE Shops
completely rewound and rebuilt the rotary converter with modern
insulation a few years ago - there's a good story behind that one, it
was supposed to go in for a dip-and-bake and minor stator coil work
(with a fixed bid), and they kept digging...

It was the technician's last hurrah before he retired. :-P

-- Bruce --
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