480 to 240 volt transformer

[augie47]

I can see it being a point of discussion, but as written, when the "neutral" is not used, I don't see that section requiring midpoint grounding, as Golddigger states.
That said, in this situation, I would choose to ground the midpoint as the simplest way to meet Code.

 

[kwired]

Where are you finding 'if used' in the sections I quoted?

"if used" is not the actual wording, but isn't "if used" a way of summarizing what is bold text below?
250.20 Alternating-Current Systems to Be Grounded.

(B) Alternating-Current Systems of 50 Volts to 1000 Volts.
Alternating-current systems of 50 volts to less than 1000 volts
that supply premises wiring and premises wiring systems shall
be grounded under any of the following conditions:


(1) Where the system can be grounded so that the maximum
voltage to ground on the ungrounded conductors
does not exceed 150 volts


(2) Where the system is 3-phase, 4-wire, wye connected in
which the neutral conductor is used as a circuit conductor


(3) Where the system is 3-phase, 4-wire, delta connected in
which the midpoint of one phase winding is used as a
circuit conductor

 

[david luchini]

"if used" is not the actual wording, but isn't "if used" a way of summarizing what is bold text below?
250.20 Alternating-Current Systems to Be Grounded.

You didn't bold any of the text in part (1)...There is no "if used" requirement in that part, and it clearly applies to the system in question.

(B) Alternating-Current Systems of 50 Volts to 1000 Volts.
Alternating-current systems of 50 volts to less than 1000 volts
that supply premises wiring and premises wiring systems shall
be grounded under any of the following conditions:


(1) Where the system can be grounded so that the maximum
voltage to ground on the ungrounded conductors
does not exceed 150 volts


(2) Where the system is 3-phase, 4-wire, wye connected in
which the neutral conductor is used as a circuit conductor


(3) Where the system is 3-phase, 4-wire, delta connected in
which the midpoint of one phase winding is used as a
circuit conductor

 

[electrofelon]

You didn't bold any of the text in part (1)...There is no "if used" requirement in that part, and it clearly applies to the system in question.

How does part 1 apply to a 120/240 high leg delta?

 

[kwired]

You didn't bold any of the text in part (1)...There is no "if used" requirement in that part, and it clearly applies to the system in question.

I see what you are saying.

Guess as is written you have to ground that "neutral" tap, but bump voltage to 240/480 and you wouldn't have to. The 240/480 delta is not so common, but they are out there, usually utility supplied open delta services for limited load applications out in the middle of nowhere. High leg is 416 volts to neutral.

 

[GoldDigger]

Where are you finding 'if used' in the sections I quoted?

My post was a typo, should have read "is *used*".
As in " when ... is used ....".
In both (B)(2) and (B)(3).

 

[iwire]

My post was a typo, should have read "is *used*".
As in " when ... is used ....".
In both (B)(2) and (B)(3).

But my point was based on (1).

 

[GoldDigger]

But my point was based on (1).

Which I did not even consider since 208V is greater than 150V.
If you are arguing that the high leg will not be connected to anything, then (1) might conceivably apply.

 

[ActionDave]

(1) Where the system can be grounded so that the maximum
voltage to ground on the ungrounded conductors
does not exceed 150 volts

There is going to be more than 150V to ground on the high leg whether it is used or not. I don't think (1) applies.

 

[peter d]

Update: I did ground the center tap. It was the simplest, least confusing option.

 

[iwire]

Which I did not even consider since 208V is greater than 150V.
If you are arguing that the high leg will not be connected to anything, then (1) might conceivably apply.

There is going to be more than 150V to ground on the high leg whether it is used or not. I don't think (1) applies.

See this is the part I do not know.


Talk to ya later.