equipment on hi leg phase

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Twoskinsoneman

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Location
West Virginia, USA NEC: 2020
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Facility Senior Electrician
I asked this question in another thread but that thread stopped getting hits so hear it is.

Is it common to install 208v equipment on the hi (B) phase of a hi leg 4 wire delta system?
 

jim dungar

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Wisconsin
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PE (Retired) - Power Systems
I asked this question in another thread but that thread stopped getting hits so hear it is.

Is it common to install 208v equipment on the hi (B) phase of a hi leg 4 wire delta system?
No.

Among other things:
Except for 480Y/277 panels, there are very few (if any) 1-pole circuit breakers rated 208V to ground.

Most of the normal 240/120V 3PH 4W transformer arrangements have not been sized to handle the imbalance caused by a Hi-Leg to Neutral connected load.
 

R Bob

Senior Member
Location
Chantilly, VA
I asked this question in another thread but that thread stopped getting hits so hear it is.

Is it common to install 208v equipment on the hi (B) phase of a hi leg 4 wire delta system?

If you are talking about using a single pole ckt brkr on "B" phase to feed a ckt that yields 208volts to ground, the answer is no.

I searched for your other thread and could not find it.
If you asked the same question, I'm sure the overwhelming response you received was no.
 

Twoskinsoneman

Senior Member
Location
West Virginia, USA NEC: 2020
Occupation
Facility Senior Electrician
If you are talking about using a single pole ckt brkr on "B" phase to feed a ckt that yields 208volts to ground, the answer is no.

I searched for your other thread and could not find it.
If you asked the same question, I'm sure the overwhelming response you received was no.

Thanks Jim. Hey R Bob, Is your reason for a no the same as Jim's: Transformer not made to handle it?

Actually the thread was about marking a hi leg and I thought I would throw my question in at the end of the thread...no responses...
 

benaround

Senior Member
Location
Arizona
This question has been asked before and I don't remember anyone citing a code that

said this was a violation. I would not attempt to do this personally. So, let's see if we can

find a NEC violation.
 

R Bob

Senior Member
Location
Chantilly, VA
Thanks Jim. Hey R Bob, Is your reason for a no the same as Jim's: Transformer not made to handle it?

Actually the thread was about marking a hi leg and I thought I would throw my question in at the end of the thread...no responses...

I think Jim and I were posting @the same time. I wasn't going to go into that much detail. His explaination is exactly the way I understand it, and he did a better of it than I would have. He is considered one the more reliable sources of info.

Back to your original question, I might add that the "high leg" is just a by product of the characteristics of the winding configuration and is not intended to be used as you suggested. In fact, I don't recall ever seeing this attempted.
 

tryinghard

Senior Member
Location
California
I asked this question in another thread but that thread stopped getting hits so hear it is.

Is it common to install 208v equipment on the hi (B) phase of a hi leg 4 wire delta system?

If the equipment is using 2 or 3 phases it is usually rated for 208 or 240V, then the use of the high leg is fine.
 

infinity

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Location
New Jersey
Occupation
Journeyman Electrician
If the equipment is using 2 or 3 phases it is usually rated for 208 or 240V, then the use of the high leg is fine.

You're correct and using a 2 pole or 3 pole CB wouldn't make it a high leg. It's only a high leg with relation to the neutral and ground.
 

jim dungar

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Location
Wisconsin
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PE (Retired) - Power Systems
To be honest with you that one I didn't follow really... Obviously breakers are made that can handle 208...
Most 240/120V systems feed "run of the mill" panelboards which do not have provisons for a 1-pole 208V L-G breaker.

If the proper breaker is used, there is no NEC violation for feeding 208V loads, however it is definitley not a good design.
 

augie47

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Location
Tennessee
Occupation
State Electrical Inspector (Retired)
I find it really fascinating that no one has done it as if it is taboo or something.

Its probably been done.... but most of the guys you speak with here try to follow Code, and, as has been pointed-out, the breaker ratings make this non-code compliant.
 

Twoskinsoneman

Senior Member
Location
West Virginia, USA NEC: 2020
Occupation
Facility Senior Electrician
... but most of the guys you speak with here try to follow Code, and, as has been pointed-out, the breaker ratings make this non-code compliant.

I'm not one to not follow the code either. I'm simply exploring if it IS a violation. What about using a two poll breaker and only wire one side of?
Where is the violation there Augie?
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
with a non-slash rated, two-pole breaker, I don't know that there woud be a Code violation. Of course, other than experimenting, I don't see the advantage either :D (since you could get 240 from the breaker itself)
Previous posts in regard to transformer design convinced me it wasn't a good idea, but if one wanted to try it........
 

Twoskinsoneman

Senior Member
Location
West Virginia, USA NEC: 2020
Occupation
Facility Senior Electrician
with a non-slash rated, two-pole breaker, I don't know that there woud be a Code violation. Of course, other than experimenting, I don't see the advantage either :D (since you could get 240 from the breaker itself)
Previous posts in regard to transformer design convinced me it wasn't a good idea, but if one wanted to try it........

We're certainly in agreement that there probably isn't any advantage to it :smile:
 

e57

Senior Member
While back there was a thread with a lot of discussion on the topic, and from what I remember the consenus being - is that the circut impedance is the real issue, as the path(s) from both sides of the circuit - on the transformer, and any other circuits - to the grounded neutral would be involved in OCP of the circuit. Any load on either A or C would be part of the circuit path, as well as those portions of the transformer.

I have no time to draw a picture, but a few words could be said by one.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
I remember reaing that any aqppreciable load connected from high leg to neutral sets up some really nasty currents in the split secondary, and that it has a poor (high) source impedance.
 
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