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

[Volt-Amps]

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.

 

[electrofelon]

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.

 

[infinity]

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.

 

[Volt-Amps]

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.

So how is this different from 120/240V, 3 Phase open delta where you have 120/208/240, with 208V on the B phase?

 

[infinity]

So how is this different from 120/240V, 3 Phase open delta where you have 120/208/240, with 208V on the B phase?

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.

 

[Gary11734]

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.

I remember it as, 57%. They always made us say, Heinz 57 sauce!

 

[infinity]

I remember it as, 57%. They always made us say, Heinz 57 sauce!

Actually 57.7%, 58 works for me.

 

[Gary11734]

Actually 57.7%, 58 works for me.

Ok, I'm with ya. I learn this in the union!


Long ago.......

 

[Gary11734]

Actually 57.7%, 58 works for me.

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...

 

[infinity]

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...

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.

 

[roger]

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.

The utility company needs to send their engineer to a good apprenticeship course.

Roger

 

[Volt-Amps]

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?.

Still need help with questions I posted earlier...Please

 

[Gary11734]

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:

Thanks for the info and code section.

 

[jim dungar]

Still need help with questions I posted earlier...Please

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.

 

[roger]

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?

1. Yes, there is a neutral from the source.

1. Would a 120/240V, 3 phase, closed delta service from utility have a high leg?

1. Yes.

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?

There is a high leg in either configuration.

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?

Yes it is.
Open or closed does not change the characteristics, it only removes one set of winding's



Roger

 

[electrofelon]

Basically from the customers standpoint, there is no difference between their service being supplied open or closed Delta, and they wouldn't even know without seeing the transformer bank.

 

[Volt-Amps]

Thank you all for your help.
Jim and Roger, spacial thanks.