Separately Derived Wye Secondary Ungrounded

[nmelectrical]

I am trying to understand where/how in the code it allows the secondary side of a WYE-WYE transformer can be ungrounded. I read in 250.30(B)(1) that you need a GEC sized properly and bonded to the metal enclosures and the grounding electrode. If I understand this correctly? if a fault occurs in a single conductor to ground then the Y system would become grounded and the other 2 conductors voltages would rise. Isn?t there something that requires ground fault detection be installed?

 

[don_resqcapt19]

If the system is not required to be a grounded system by the rules in 250.20, then 250.21(B) requires ground detection.

 

[nmelectrical]

So assuming that we use 12.47/480 WYE-WYE xformer.

Spelling this out...250.20(D) directs us at a system in 250.20 (B) and requires us to use 250.30(A) to ground the system. The only way (i know it's unwise) to have an ungrounded sep. derived sys that's WYE is if it is something in the 250.21(A)...or use a DELTA secondary.

 

[raider1]

So assuming that we use 12.47/480 WYE-WYE xformer.

Spelling this out...250.20(D) directs us at a system in 250.20 (B) and requires us to use 250.30(A) to ground the system. The only way (i know it's unwise) to have an ungrounded sep. derived sys that's WYE is if it is something in the 250.21(A)...or use a DELTA secondary.

Not necessarily, if the WYE secondary is 480 volts and the neutral is not used as a circuit conductor then 250.20(B) does not require that the system be grounded.

Chris