High Leg Grounded B

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dvcraven0522

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St. Louis, Missouri
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I have and and existing service fed from (3) utility mounted xfmrs. The service disconnect says 480/277V. Down steam there is a 480/277V panel and transformer. Transformer feeds a panel that is mark high led on all breaker with B phase tape over.

I don't understand the how you can have 480/277V service if the utility is bring in a grounded B service drop.

I must be missing something?

Dan
 
Can you explain a but more ? I don't understand the question.
The transformer could supply a grounded B phase panel regardless of what type primary was used.
 
You either have a High Leg or you have a grounded B phase, you cannot have both.

Unless you have only multipole breakers it is a sure bet you have a High Leg 240/120 3phase 4wire output on your transformer.
 
I’m not sure where you are thinking the grounded B phase is. You should get more clarity on what you really have.

If the 480V PRIMARY were a grounded B phase, then whatever the secondary of your 2nd transformer is becomes irrelevant, it is a separate system. The fact that one of the primary legs is grounded means nothing to the secondary of that transformer.

But if your 480V is a grounded B phase, it is NOT 480/277, it is straight 480V and that’s important because of the breakers you need on that system.

if you are thinking your 240/120V secondary of that transformer is a grounded B phase, that would be incorrect IF you have 1 pole breakers in that panel, because that would confirm that you have a 120V center tap on one winding of the transformer.

If on the other hand that secondary panel is all 2 and 3 pole breakers, then it COULD be a 240V 3 phase 3 wire system where one phase is grounded and the B phase poles being taped off is just because someone was thinking that phase could not be used because it is grounded (incorrect by the way). You would NOT have any 120V loads from that however.
 
dvcraven0522 said:
I have and and existing service fed from (3) utility mounted xfmrs. The service disconnect says 480/277V. Down steam there is a 480/277V panel and transformer. Transformer feeds a panel that is mark high led on all breaker with B phase tape over.

I don't understand the how you can have 480/277V service if the utility is bring in a grounded B service drop.

I must be missing something?

Dan
Click to expand...
You need to clarify what you have. As mentioned you can have grounded phase or you can have 480/277 but can't have both.

The separately derived system can be high leg system regardless of what the primary supply is, does need to be three phase system or electronically inverted into three phase output though to come from conventional transformation.
 
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