bond jumper for transformers

[erock1]

I have a 112.5 kva transformer 480 to 120/208. My question is I have paralleled 4/0's to my 400 amp low volt panel, how would you size the the bond jumper for parallel feeds (xo to frame). The code book says to size it to the latest ungrounded conductor but nothing about parallel runs. Do I just size it to one of the ungrounded conductor or do I have to go to tables and find the total area of two # 2's from table 250.66 for each run.

 

[augie47]

For the system bonding jumper you would size per 250.66 for the sum of the kcmils of the paralleled conductors (2 4/0 @ 211600 ea =423,200 for a 1/0 jumper)
If your parallel feeds are in separate conduits you can size the equipment bonding jumpers by the size of the conductor in each conduit {see 250.102(C)}

 

[infinity]

I have a 112.5 kva transformer 480 to 120/208. My question is I have paralleled 4/0's to my 400 amp low volt panel, how would you size the the bond jumper for parallel feeds (xo to frame). The code book says to size it to the latest ungrounded conductor but nothing about parallel runs. Do I just size it to one of the ungrounded conductor or do I have to go to tables and find the total area of two # 2's from table 250.66 for each run.

The notes to table 250.66 mention what to do when you have parallel conductors.

Notes:
1. Where multiple sets of service-entrance conductors are used as
permitted in 230.40, Exception No. 2, the equivalent size of the larg-
est service-entrance conductor shall be determined by the largest sum
of the areas of the corresponding conductors of each set.
2. Where there are no service-entrance conductors, the grounding
electrode conductor size shall be determined by the equivalent size of
the largest service-entrance conductor required for the load to be
served.
a This table also applies to the derived conductors of separately de-
rived ac systems.

As Augie stated you would use the total conductor area of the parallel sets and find the value in T250.66 to size the system bonding jumper.

 

[erock1]

For the system bonding jumper you would size per 250.66 for the sum of the kcmils of the paralleled conductors (2 4/0 @ 211600 ea =423,200 for a 1/0 jumper)
If your parallel feeds are in separate conduits you can size the equipment bonding jumpers by the size of the conductor in each conduit {see 250.102(C)}

That's awesome, thank you!

 

[erock1]

The notes to table 250.66 mention what to do when you have parallel conductors.




As Augie stated you would use the total conductor area of the parallel sets and find the value in T250.66 to size the system bonding jumper.

Thanks, I didn't even bother to look at the notes under t250.66. Then I was trying to use table 8 to find the area which is the the wrong table, table 5 is what I wanted. Thanks for clearing everything up for me, I appreciate it.