Bonding Jumper supply side

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Transportation Guy

Senior Member
Location
Williamsburg,VA
Good afternoon fellow professionals. We have an 800 amp service . Leaving the CT are 3 (parallel) sets of (4) 400MCM aluminum conductors in metal raceway. We need to bond these raceways. Based on 250.102 ( C) (1) our inspector says we can use a 1/0 copper. I dont agree. The chart says " Size of ungrounded conductor OR equivalent area for parallel conductors." Based on this, I dont use the largest ungrounded conductor to size this, I use the area of the ungrounded conductors since we are in parallel. By doing this, I exceed the chart (over 1750 kcmil because I have 9 ungrounded 400's which equal 3600 kcmil) The notes below the chart tell me I cannot be less than 12.5% of the equivalent area of ungrounded conductors but do not have to be larger than the largest ungrounded conductor. I calculate I need a 400kcmil as a bonding jumper for these raceways entering my service disconnect.

GO!!
 

Jim1959

Senior Member
Location
Longmont, CO
I believe you only have to add up the conductors in one raceway or cable, not all the ungrounded conductors.

(2) Size for Parallel Conductor Installations in Two or More
Raceways or Cables. Where the ungrounded supply conductors
are paralleled in two or more raceways or cables, and an individual
supply-side bonding jumper is used for bonding these raceways
or cables, the size of the supply-side bonding jumper for each
raceway or cable shall be selected from Table 250.102(C)(1)
based on the size of the ungrounded supply conductors in each
raceway or cable. A single supply-side bonding jumper installed
for bonding two or more raceways or cables shall be sized in
accordance with 250.102(C)(1).

I agree with the inspector as well.
 

Jim1959

Senior Member
Location
Longmont, CO
By definition, all the ungrounded conductors are not paralleled, only the ungrounded conductors of one phase or leg of the system. So, you would multiply 3 times 400 MCM, and have an equivalent of 1200 MCM aluminum, which looks like it would require a 2/0 copper.
 

Smart $

Esteemed Member
Location
Ohio
(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).

(2) Size for Parallel Conductor Installations in Two or
More Raceways. Where the ungrounded supply conductors
are paralleled in two or more raceways or cables, and
an individual supply-side bonding jumper is used for bonding
these raceways or cables, the size of the supply-side
bonding jumper for each raceway or cable shall be selected
from Table 250.102(C)(1) based on the size of the ungrounded
supply conductors in each raceway or cable. A
single supply-side bonding jumper installed for bonding
two or more raceways or cables shall be sized in accordance
with 250.102(C)(1).
You have to size per (C)(1) or (C)(2). The latter permits you to run a smaller individual BJ to each raceway. If you run one BJ to all raceways, you must size per the former.

3 sets of 400kcmil Al in 3 conduits

#2 Cu or 1/0 Al to each raceway
—or—​
2/0 Cu or 4/0 Al to all three raceways​
 
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