Transformer Ground wires for two panelboards within 10' tapped from transformer

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jjs

Member
Location
Puryear, TN, USA
I have a 150kva 480v single phase primary with 240/120v single phase secondary xfmr. It is intended to feed (2) 400A 240/120v MCB panelboards with #600kcmil to each. The neutral is bonded in the transformer and a 3/0 is used. If a ground wire is installed in the conduit from the transformer to each panelboard, is it sized per T250.66? Or is it sized per T250.122?
so is the feeder supposed to be 3#600kcmil, 1#3/0G ?
or is the feeder supposed to be 3#600kcmil, 1#3G ?
Or is it something else all together?
Thanks
 

packersparky

Senior Member
Location
Wisconsin
Occupation
Inspector
I have a 150kva 480v single phase primary with 240/120v single phase secondary xfmr. It is intended to feed (2) 400A 240/120v MCB panelboards with #600kcmil to each. The neutral is bonded in the transformer and a 3/0 is used. If a ground wire is installed in the conduit from the transformer to each panelboard, is it sized per T250.66? Or is it sized per T250.122?
so is the feeder supposed to be 3#600kcmil, 1#3/0G ?
or is the feeder supposed to be 3#600kcmil, 1#3G ?
Or is it something else all together?
Thanks


The "ground" wire from the transformer to the panels is a supply side bonding jumper and is sized per Table 250.102(C).
 

jjs

Member
Location
Puryear, TN, USA
Thanks.
So Do you use the combined feeders to determine the supply side bonding jumper, and run that large jumper to each? So in this case that would be 1200kcmil worth of feeder.
Or do you use the 600kcmil for each feeder, and then provide that size supply side bonding jumper to each?
I don't have parallel conductors, i have one set feeding one panelboard and another set feeding another panelboard.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
You would size the SSBJ based on the size of the ungrounded conductors in each raceway. So for 600 kcmil you would need a #1/0 in each raceway as the SSBJ.

250.102(C) Size — Supply-Side Bonding Jumper.
(1) Size for Supply Conductors in a Single Raceway or Cable. The supply-side bonding jumper shall not be smaller than specified in Table 250.102(C)(1).
 
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