Transformer wiring.

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habit044

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I have a transformer that is 14.4k to 480/277. Secondary side is 1000Amps

Customer provided this transformer. However everything we are using is 3 Phase only. No neutral required for anything!(480v 3 phase motors only)
My question is three parts...

Do we have to bring out the neutral out of this transformer even though we are not using it at all?

Second if we do HAVE to install the neutral, what is the smallest size we can use? Can this be smaller than my 3-phase hot wires?

I do know if we do have to use all of these then we have to de-rate our wire since there is more than 3 current carrying conductors.

Where in the 2008NEC does it say yea or nay to do this? If it says it at all....

Also this is in small plant, in Texas.


Thanks!
 
Welcome to the forum.:)

Take a look at 250.20 and 250.21 for the requirements for system grounding.

Also check out 250.30 for the requirements for grounding of separately derived systems where grounding is required or preferred.

Chris
 
habit044 said:
Customer provided this transformer. However everything we are using is 3 Phase only. No neutral required for anything!(480v 3 phase motors only)
...
I do know if we do have to use all of these then we have to de-rate our wire since there is more than 3 current carrying conductors. ...
Click to expand...
If there is no load connected to the neutral, it is not a current carrying conductor and would not have any effect on the derating of the phase conductors.
 
Thanks for the welcome!
I looked at those sections, still not quite what im looking for...Thank though!

And as far as it not being a current carrying conductor, rather it is used or not im sure the de-rating applies if it is there. I can see myself arguing that one with an inspector. My thinking is why even bring it out if it is not used!

The company we are working with says the power company told them it is CODE to bring the neutral out even if we are not using it......The run is 300' away and this is a bid we are trying to keep the money as low as we can.
I can't find this code...
 
habit044 said:
Thanks for the welcome!
I looked at those sections, still not quite what im looking for...Thank though!

And as far as it not being a current carrying conductor, rather it is used or not im sure the de-rating applies if it is there. I can see myself arguing that one with an inspector. My thinking is why even bring it out if it is not used!

The company we are working with says the power company told them it is CODE to bring the neutral out even if we are not using it......The run is 300' away and this is a bid we are trying to keep the money as low as we can.
I can't find this code...
Click to expand...

Is it a service transformer? If so, and the service disconnecting means is on the load side of the transformer, yes you will have to bring out a neutral conductor... at least to the service disconnect.

The neutral conductor can be no smaller than the minimum GEC per 250.66.
 
Smart $ said:
Is it a service transformer? If so, and the service disconnecting means is on the load side of the transformer, yes you will have to bring out a neutral conductor... at least to the service disconnect.

The neutral conductor can be no smaller than the minimum GEC per 250.66.
Click to expand...
Of course I assumed the secondary will be a grounded system. Reference 250.24(C)... and don't forget to apply the rest of 250.24...

PS: The neutral in this case is not a current-carrying conductor so it is not counted for derating purposes, only as raceway fill.
 
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habit044 said:
...
And as far as it not being a current carrying conductor, rather it is used or not im sure the de-rating applies if it is there. I can see myself arguing that one with an inspector. My thinking is why even bring it out if it is not used!
Click to expand...
Many grounded conductors, even when used, are not current carrying conductors for the purpose of derating. Take a look at 310.15(B)(4).
 
Groung the neutral point at the secondary. Take the three phase conductors to your load along with an equipment grounding conductor. You do not have to carry the neutral to your load. If you did it would not be considered a current carrying conductor, NEC 310-159(B)(4)(a).
 
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