System bonding jumper sizing NEC 250.30

[PerigonRobert]

I have a 1500 KVA (4160 Delta/ 480 Wye) transformer connected to a 3phase-3wire system (no neutral). Grounded at the X0 transformer terminal within the transformer secondary.

Secondary wiring is 6 parallel underground conuits with 3-350kcmils phase conducter per conduit.

My question is how large must the System Bonding Jumper be for each raceway (conduit)?

 

[dpc]

Each one must be fully-sized per the table, based on the total cross-sectional area of the phase conductors. If there is a ground fault in one conduit, virtually 100% of the ground current will flow in the ground wire inside that conduit, so it has to be fully-sized.

 

[PerigonRobert]

Thanks dpc --

The 12.5% calculation for 6 X 350kcmils =~ 300kcmils and to purcahse commerically available wire

I would need 350kcmils bare copper; therfore, each conduit would contain (3) 350kcmils insulated phase conductors and (1) 350kcmils bare copper cable.

Thanks again

 

[dpc]

Sounds about right. It doesn't have to be bare, BTW.