Transformer requirements

[Danny herb]

I feel like I have to preface my question because my last thread got closed.

I have been in the electrical industry for about 14 years. I used to work for a GC, then an Electrical Contractor, and then in the film/TV/Event industry as an electrician. But I never joined the union, went through any schooling or taken my contractor/certification test so I am not as knowledgeable about the real technical stuff. So I apologize if my wording/writing of the terms are not perfect.

Now, I have a 300a "High-leg" delta service that I need to change into the standard 120-120-120v service. But I am having a hell of a time trying to find the right transformer. Any advice would be helpful. Thanks!

 

[ggunn]

I feel like I have to preface my question because my last thread got closed.

I have been in the electrical industry for about 14 years. I used to work for a GC, then an Electrical Contractor, and then in the film/TV/Event industry as an electrician. But I never joined the union, went through any schooling or taken my contractor/certification test so I am not as knowledgeable about the real technical stuff. So I apologize if my wording/writing of the terms are not perfect.

Now, I have a 300a "High-leg" delta service that I need to change into the standard 120-120-120v service. But I am having a hell of a time trying to find the right transformer. Any advice would be helpful. Thanks!

It seems to me that all you need is a 240V delta to 208/120V wye transformer. The high leg is not an issue because you would not connect the neutral on the primary (240V) side. You would ground the neutral on the secondary (208V) side. I believe that 125kVA would be your minimum size.

It should be fairly easy to find.

 

[templdl]

I feel like I have to preface my question because my last thread got closed.

I have been in the electrical industry for about 14 years. I used to work for a GC, then an Electrical Contractor, and then in the film/TV/Event industry as an electrician. But I never joined the union, went through any schooling or taken my contractor/certification test so I am not as knowledgeable about the real technical stuff. So I apologize if my wording/writing of the terms are not perfect.

Now, I have a 300a "High-leg" delta service that I need to change into the standard 120-120-120v service. But I am having a hell of a time trying to find the right transformer. Any advice would be helpful. Thanks!

Are you a licensed electrician familiar with a 208y/120 3phase, 4wire service? Taking a wild ass guess that seems to be what you are asking for.

 

[JFletcher]

I feel like I have to preface my question because my last thread got closed.

I have been in the electrical industry for about 14 years. I used to work for a GC, then an Electrical Contractor, and then in the film/TV/Event industry as an electrician. But I never joined the union, went through any schooling or taken my contractor/certification test so I am not as knowledgeable about the real technical stuff. So I apologize if my wording/writing of the terms are not perfect.

Now, I have a 300a "High-leg" delta service that I need to change into the standard 120-120-120v service. But I am having a hell of a time trying to find the right transformer. Any advice would be helpful. Thanks!

Do you own the transformers, or the POCO? You may want to contact them to change the 240V open delta to a 208Y/120 service.

If ggunn is correct in the 125kva assessment, then something like this is what you need:

http://www.gordonelectricsupply.com...ocess~search?gclid=CLjvz6WV4M4CFYdcfgod0moKyQ

240V delta primary, 208V wye secondary

 

[Danny herb]

Are you a licensed electrician familiar with a 208y/120 3phase, 4wire service? Taking a wild ass guess that seems to be what you are asking for.

I have always worked under my boss's licenses. I, myself, am not licensed. But now I have my own building and I'm trying to find a used transformer that isn't $5k. I am most familiar with 240/120 services. (line to line 240v, line to neutral 120v) That's what I'm trying to get to.

 

[Danny herb]

Do you own the transformers, or the POCO? You may want to contact them to change the 240V open delta to a 208Y/120 service.

If ggunn is correct in the 125kva assessment, then something like this is what you need:

http://www.gordonelectricsupply.com...ocess~search?gclid=CLjvz6WV4M4CFYdcfgod0moKyQ

240V delta primary, 208V wye secondary

I'm confused. Why would I go down to 125kva when I need 300 amps? And why does it have to be 208? Shouldn't it be 240? I'm just trying to get rid of that high leg, so that the new service can handle 3-phase power with 120v on each leg, at 300A.

 

[GoldDigger]

I have always worked under my boss's licenses. I, myself, am not licensed. But now I have my own building and I'm trying to find a used transformer that isn't $5k. I am most familiar with 240/120 services. (line to line 240v, line to neutral 120v) That's what I'm trying to get to.

By the most common identification system, the possibilities are:

1. Single phase three wire, 120-0-120, referred to as 120/240 (in that order). Also 120/240 single phase three wire.
2. Three phase high leg delta, sometimes written as 240/120 three phase four wire. The voltage from the third phase wire (high leg) to neutral is 208, so just saying 120 line to neutral is not a complete or accurate description.
3. Three phase wye, written 208Y/120 (with or without the qualifier three phase, four wire.)

 

[Smart $]

I'm confused. Why would I go down to 125kva when I need 300 amps? And why does it have to be 208? Shouldn't it be 240? I'm just trying to get rid of that high leg, so that the new service can handle 3-phase power with 120v on each leg, at 300A.

125kVA 208Y/120V 3Ø 4W transformer has a rated output of 347A.


The only 3Ø system with 120V from each line to neutral is 208Y/120V 3Ø 4W. However, as indicated, line-line is 208V.

You already have the only system that has 240V line-line and 120V line-neutral, but not high leg to neutral.

 

[Danny herb]

125kVA 208Y/120V 3Ø 4W transformer has a rated output of 347A.


The only 3Ø system with 120V from each line to neutral is 208Y/120V 3Ø 4W. However, as indicated, line-line is 208V.

You already have the only system that has 240V line-line and 120V line-neutral, but not high leg to neutral.

Right. Okay, so what I've been missing this whole time is that if I need 300 amps, I don't get a 300kva transformer? I get a 125kVA transformer with the primary being 240 delta and the secondary being 208Y/120?

 

[Smart $]

Right. Okay, so what I've been missing this whole time is that if I need 300 amps, I don't get a 300kva transformer? I get a 125kVA transformer with the primary being 240 delta and the secondary being 208Y/120?

Correct. 300A × 208V × square root (3) = 300A × 120V × 3 = 108,000VA or 108kVA

If you are changing over the whole building, why not check with the POCO (power company) about changing over the service to 208/120?

 

[Danny herb]

Correct. 300A × 208V × square root (3) = 300A × 120V × 3 = 108,000VA or 108kVA

If you are changing over the whole building, why not check with the POCO (power company) about changing over the service to 208/120?

Okay. I get it now. I'm pulling permits and whatnot, so B&S and POCO are already in my sights. I'm just trying to get the right transformer. I'm not changing the whole building over, I'm just putting in a sub-panel from the main service, that needs to be 300A three phase.
Thank you. This clears up a lot.

 

[augie47]

The original on this subject was closed by a Moderator as the OP is not currently in the trade. His question has now been covered and any additional information would tend to support a DIY situation. For that reason, after conferring with other Mods, I am closing this thread