Transformer grounding

[Gregory Chipps]

If I have a 480/277v transformer feeding a service entrance rated 480v,
1200a, 3wire MCC (no 277v) and I ground the transformer neutral at the
transformer (not bring it into the MCC and ground to the ground bus
since there is no neutral bus) do I require ground fault protection.

THANKS

 

[don_resqcapt19]

If the transformer is grounded, then you must bring the grounded conductor to the service equipment. 250.24(C). Gound fault protection is required.
Don

 

[jim dungar]

250.24(C) deals with voltage to ground on solidly grounded systems. It does not care if a grounded conductor is actually present. This is one reason, high resistance grounds are becoming more common.

 

[don_resqcapt19]

Jim,

250.24(C) deals with voltage to ground on solidly grounded systems. It does not care if a grounded conductor is actually present.

I don't understand. If XO is grounded at the transformer, then the grounded conductor must be run to the service equipment.

250.24(C) Grounded Conductor Brought to Service Equipment Where an ac system operating at less than 1000 volts is grounded at any point, the grounded conductor(s) shall be run to each service disconnecting means and shall be bonded to each disconnecting means enclosure.

Don

 

[jim dungar]

Don,

Another example of trusting my memory for code articles.
I wanted to refer to 240.13 for GF protection

250.24(C) requires the grounded conductor to be brought to the service disconnecting means. But it does not require the grounded conductor be be continued past the service point. If the wye transformer is an SDS 250.30 (A)(1) allows but does not require the grounded conductor to leave the SDS.

IMHO, 240.13 applies to all "main disconnects" even on the output of an SDS.