transformer neutral and eg

[domelectric]

I am installing a 2500A service for a glass tempering furnace. From the switch gear I am also feeding a 480-120/208V 3 phase 75 KVA transformer which in turn supplies a 3 phase 120/208 MB panel. The plans call for four 3/0 and one number 6 eg. I look at this set up as a separately derived system and would not need to separate the eg conductor and the neutral in the 120/208 panel. So why would I need a separate eg conductor? I think just running the three phase conductors and the neutral conductor, install the bonding strap, and be done with it. I have bonded the transformer to the building steel. Any thoughts would help. Thanks.

 

[RUWired]

I look at this set up as a separately derived system and would not need to separate the eg conductor and the neutral in the 120/208 panel. So why would I need a separate eg conductor? I think just running the three phase conductors and the neutral conductor, install the bonding strap, and be done with it. I have bonded the transformer to the building steel. Any thoughts would help. Thanks.

Dome, article 250.30(A)1 requires the system bonding jumper to be installed either at the transformer or the first OCPD, not both, except exception # 2 but being in an industrial plant i doubt that would apply. It also states the bonding jumper goes where the GEC is installed.

Rick

 

[infinity]

Is this copper or aluminum? For #3/0 Cu secondary conductors the bonding jumper should be a #4 not a #6.