Large XFMR Ckt conductors

[KarlS]

I provide metal interlocking buildings with switchgear etc.

Many times the Switchgear is rated for service entrance. Most it's not. Usually there is a large 500, 1000, or 1500KVA transformer sitting outside on a pad. Sometimes the connection is busduct but usually cables. I do the buildings but not the XFMR to building connection.

My question is for the experianced installers on the site. Do you bring the circuit conductors with a ground back to the switchgear or do you just run the (3) circuit conductors?

Also, is the GEC with N-Gnd bond at the transformer or at the switchgear? I am told some run the gnd back to the switchgear and others do not. If the GEC is at the XFMR I am sure your circuit conductors will have a gnd.

 

[KarlS]

Bump???

Bump???

Any feedback would be great!

 

[augie47]

If I understand your question, this may help:

If your transformer is set up for a grounded system (208Y/120; 480Y/277) then you must bring the grounded conductor to the service.

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 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)(3).

Their will normally be a neutral ground at the transformer:

250.24(A)(2) Outdoor Transformer. Where the transformer supplying the service is located outside the building, at least one additional grounding connection shall be made from the grounded service conductor to a grounding electrode, either at the transformer or elsewhere outside the building.

And a neutral-ground connection at the service

250.24(B) Main Bonding Jumper. For a grounded system, an unspliced main bonding jumper shall be used to connect the equipment grounding conductor(s) and the service-disconnect enclosure to the grounded conductor within the enclosure for each service disconnect in accordance with 250.28.


If your system is ungrounded 240, 480 delta), different rules apply