120/240V, 3 Phase, 3 transformers on pole, closed delta

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Volt-Amps

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The utility engineer said we will be getting our 3 phase power from a pole with 3 transformers. The service will be 120/240V, 3 phase. I asked if it's a high leg, he said closed delta and open delta are different, there is no high leg in a closed delta system and connecting to phase B is no problem.

Maybe I am doing too much reading on the internet because of the conflicting information I am getting. Could the experts please help with the following questions:


  1. Would a 120/240V, 3 Phase closed delta service be a 3-phase, 4 wire or 3 phase, 3 wire? Would there be a neutral coming from utility?
  2. Would a 120/240V, 3 phase, closed delta service from utility have a high leg?
  3. If no high leg, does this mean on I can distribute loads anyway I want in my panel schedule without concern regarding phase B?
  4. If there is a high leg, is it similar to open delta with two transformers on the pole where phase B can't be used for 120V circuits?

I appreciate all the help.
 
He is incorrect, or something was misunderstood. Open vs closed Delta doesn't have anything to do with whether there is a high leg. Sounds like you will be getting a high leg as that is the only way to get 120v.
 
If I remember correctly the closed Delta is made up of 3 transformers instead of two for the open Delta. Since you're getting 240 volts and 120 volts as Electro stated one of the transformers will have a center tap. You should end up with a 120/208/240, 3Ø, 4W Delta.
 
infinity said:
If I remember correctly the closed Delta is made up of 3 transformers instead of two for the open Delta. Since you're getting 240 volts and 120 volts as Electro stated one of the transformers will have a center tap. You should end up with a 120/208/240, 3Ø, 4W Delta.
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So how is this different from 120/240V, 3 Phase open delta where you have 120/208/240, with 208V on the B phase?
 
Volt-Amps said:
So how is this different from 120/240V, 3 Phase open delta where you have 120/208/240, with 208V on the B phase?
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I think it has to do with capacity. If I remembering correctly from apprentice school 30 years ago the open Delta gives you 58% of the closed Delta capacity. Someone will correct me if I've gotten it wrong. :)
 
infinity said:
I think it has to do with capacity. If I remembering correctly from apprentice school 30 years ago the open Delta gives you 58% of the closed Delta capacity. Someone will correct me if I've gotten it wrong. :)
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I remember it as, 57%. They always made us say, Heinz 57 sauce!
 
Gary11734 said:
I think they taught us the 57 because I believe it's 75% less efficient than closed. So you would flip the numbers to remember both. At least that is in my head...
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I thought about it a little and it rang a bell for me because we occasionally need to calculate conductors for Wye-start Delta-run fire pumps using this code section:

430.22(C) Wye-Start, Delta-Run Motor. For a wye-start, delta-
run connected motor, the ampacity of the branch-circuit
conductors on the line side of the controller shall not be
less than 125 percent of the motor full-load current as de-
termined by 430.6(A)(1). The ampacity of the conductors
between the controller and the motor shall not be less than
72 percent of the motor full-load current rating as deter-
mined by 430.6(A)(1).
Informational Note: The individual motor circuit conduc-
tors of a wye-start, delta-run connected motor carry 58 per-
cent of the rated load current. The multiplier of 72 percent
is obtained by multiplying 58 percent by 1.25.
Click to expand...
 
Volt-Amps said:
The utility engineer said we will be getting our 3 phase power from a pole with 3 transformers. The service will be 120/240V, 3 phase. I asked if it's a high leg, he said closed delta and open delta are different, there is no high leg in a closed delta system and connecting to phase B is no problem.
Click to expand...
The utility company needs to send their engineer to a good apprenticeship course.

Roger
 
infinity said:
The utility engineer said we will be getting our 3 phase power from a pole with 3 transformers. The service will be 120/240V, 3 phase. I asked if it's a high leg, he said closed delta and open delta are different, there is no high leg in a closed delta system and connecting to phase B is no problem.


  1. Would a 120/240V, 3 Phase closed delta service be a 3-phase, 4 wire or 3 phase, 3 wire? Would there be a neutral coming from utility?
  2. Would a 120/240V, 3 phase, closed delta service from utility have a high leg?
  3. If no high leg, does this mean on I can distribute loads anyway I want in my panel schedule without concern regarding phase B?
  4. If there is a high leg, is it similar to open delta with two transformers on the pole where phase B can't be used for 120V circuits?.
Click to expand...

:D:D:D Still need help with questions I posted earlier...Please
 
Volt-Amps said:
:D:D:D Still need help with questions I posted earlier...Please
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You will have a neutral between the A and C phases.
You will have a high leg.
You cannot distribute your 1 phase loads equally across all 3 phases.
240/120V 3PH 4W is available from both open-delta and closed-delta configurations. This is a design choice by the utility.
 
Volt-Amps said:
  1. Would a 120/240V, 3 Phase closed delta service be a 3-phase, 4 wire or 3 phase, 3 wire? Would there be a neutral coming from utility?
Click to expand...
  1. Yes, there is a neutral from the source.
Volt-Amps said:
  1. Would a 120/240V, 3 phase, closed delta service from utility have a high leg?
Click to expand...
  1. Yes.
Volt-Amps said:
  1. If no high leg, does this mean on I can distribute loads anyway I want in my panel schedule without concern regarding phase B?
Click to expand...
There is a high leg in either configuration.

Volt-Amps said:
If there is a high leg, is it similar to open delta with two transformers on the pole where phase B can't be used for 120V circuits?
Click to expand...
Yes it is.
Open or closed does not change the characteristics, it only removes one set of winding's



Roger
 
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