Sizing SSBJ

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quantum

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Transformer secondary to Main Breaker.
4 x 350KCM per phase (4 parallel feeds)
2 sets per conduit (2 x A, 2 x B, 2 x C, 1 x SSBJ in each conduit)

Using 250.102(C)(2) and Table 250.102(C)(1) Note 3, would I take the parallel set in one conduit (350KCM x 2 = 700KCM (i.e. Phase A plus Phase A in conduit 1)) to size the SSBJ or would I take the total of all phases (350 x 4 = 1400KCM (All Phase A's in both conduits)) to size the SSBJ? I believe it's the prior, but the note is not very clear.
 
The SSBJ in each raceway is sized according to the conductors in each raceway. So convert your parallel conductors to a single conductor and look the size up in the table.
 
infinity said:
The SSBJ in each raceway is sized according to the conductors in each raceway. So convert your parallel conductors to a single conductor and look the size up in the table.
Click to expand...
That's what I assumed, but I like a second opinion! Now for a follow-up question:
Table 250.102(C)(1) Note 3 ......... the equivalent size of the largest ungrounded supply conductor(s) shall be determined by the largest sum of the areas of the corresponding conductors of each set.
Would a set constitute the set in a raceway (A, B, C, SSBJ) or would it be a set of all A phase, a set of all B phase, etc.? What consists of a set?
 
quantum said:
That's what I assumed, but I like a second opinion! Now for a follow-up question:
Table 250.102(C)(1) Note 3 ......... the equivalent size of the largest ungrounded supply conductor(s) shall be determined by the largest sum of the areas of the corresponding conductors of each set.
Would a set constitute the set in a raceway (A, B, C, SSBJ) or would it be a set of all A phase, a set of all B phase, etc.? What consists of a set?
Click to expand...
The SSBJ would be sized for the sum of the largest of A, B or C (in rare cases they may not all be the same). In your case that would be 2 X 350 for a sum of 700 as the basis to size the SSBJ for that raceway which would be a 2/0 CU or a 4/0 AL SSBJ.
The set is not the sum of all the conductors in the raceway.
 
infinity said:
The SSBJ in each raceway is sized according to the conductors in each raceway. So convert your parallel conductors to a single conductor and look the size up in the table.
Click to expand...

IMO (C)(2) is poorly worded and needs work:

(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).
Click to expand...

I am not really sure what their intent was here, but it sounds like they are discussing sizing a SSBJ to bond a parallel raceway, not paralleling the SSBJ itself. IMO it is not clear that an SSBJ can be paralleled.
 
electrofelon said:
IMO (C)(2) is poorly worded and needs work:



I am not really sure what their intent was here, but it sounds like they are discussing sizing a SSBJ to bond a parallel raceway, not paralleling the SSBJ itself. IMO it is not clear that an SSBJ can be paralleled.
Click to expand...
I agree. For multiple raceways. However, on larger services it is often just not practical to use a single jumper.
 
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