480/277 grounded conductor to first disconnect.

[usmc80]

If I have a 480/277 secondary on transformer and the building does not have any 277volt loads. Am I required to bring in the grounded conductor and is it require to be the same size as the ungrounded conductors?

 

[iwire]

If I have a 480/277 secondary on transformer and the building does not have any 277volt loads. Am I required to bring in the grounded conductor and is it require to be the same size as the ungrounded conductors?

Required? Maybe.

But as a practical mater if you do not bring it in your other choice will be making it a corner grounded delta service or if it meets the requiments ungrounded with ground fault indicators.

I think I would bring it in.

The minimum size is based on the following.

230.42 Minimum Size and Rating.
(C) Grounded Conductors. The grounded conductor
shall not be smaller than the minimum size as required
by 250.24(C).

250.24 Grounding Service-Supplied Alternating-Current
Systems.

(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 routed with the ungrounded conductors to each service
disconnecting means and shall be connected to each disconnecting
means grounded conductor(s) terminal or bus. A
main bonding jumper shall connect the grounded conductor(
s) to each service disconnecting means enclosure. The
grounded conductor(s) shall be installed in accordance with
250.24(C)(1) through (C)(4).

 

[don_resqcapt19]

If this is not a service, you are not required to bring the grounded conductor to the first disconenct, but you will have to install the main bonding jumper at the transformer and run a supply side bonding jumper from the transformer to the first disconnect.
If this is a service, then as Bob said, you must run the grounded conductor from the transformer to the service disconnect.

 

[kwired]

If it is service conductors and the neutral is the point that is grounded then Bob has the section that applies in his post, but did not post all of that section. You most likely will end up sizing it to T250.66, or if paralleled service conductors in more than one raceway it is still 250.66 but is not to be smaller than 1/0 AWG.