250.66

[dkidd]

There was an old thread about sizing the conductor that I don't know if ever effected anything

http://forums.mikeholt.com/showthread.php?t=76013

 

[infinity]

250.104(A)(1) and 250.104(C) both require conductor sizing per Table 250.102(C)(1) and the 12.5% rule is part of that table.

The *note to that table says that it applies only to the SBJ, SSBJ and MBJ.

 

[Smart $]

The *note to that table says that it applies only to the SBJ, SSBJ and MBJ.

It does not say the table applies only to MBJ's, SBJ's, and SSBJ's. But even if it did, the table still applies to sizing bonding jumpers referred to this table in 250.104.

 

[infinity]

It does not say the table applies only to MBJ's, SBJ's, and SSBJ's. But even if it did, the table still applies to sizing bonding jumpers referred to this table in 250.104.

Notes:1. If the ungrounded supply conductors are larger than 1100 kcmil
copper or 1750 kcmil aluminum, the grounded conductor or bonding
jumper shall have an area not less than 12 1 ∕ 2 percent of the area of the
largest ungrounded supply conductor or equivalent area for parallel
supply conductors. The grounded conductor or bonding jumper shall
not be required to be larger than the largest ungrounded conductor or
set of ungrounded conductors.
2. If the ungrounded supply conductors are larger than 1100 kcmil
copper or 1750 kcmil aluminum and if the ungrounded supply
conductors and the bonding jumper are of different materials (copper,
aluminum, or copper-clad aluminum), the minimum size of the
grounded conductor or bonding jumper shall be based on the assumed
use of ungrounded supply conductors of the same material as the
grounded conductor or bonding jumper and will have an ampacity
equivalent to that of the installed ungrounded supply conductors.
3. If multiple sets of service-entrance conductors are used as permitted
in 230.40, Exception No. 2, or if multiple sets of ungrounded supply
conductors are installed for a separately derived system, 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.
4. If there are no service-entrance conductors, the supply conductor
size shall be determined by the equivalent size of the largest service-
entrance conductor required for the load to be served.
*For the purposes of applying this table and its notes, the term bonding
jumper refers to main bonding jumpers, system bonding jumpers, and
supply-side bonding jumpers.

I'm referring to the 12.5% rule. If a bonding jumper is not one of those then I don't see how the 12.5% rule mentioned in note #1 applies.

 

[Smart $]

I'm referring to the 12.5% rule. If a bonding jumper is not one of those then I don't see how the 12.5% rule mentioned in note #1 applies.

Because a bonding jumper is not listed in the title either... and yet 250.104 sends you to Table 250.102(C)(1) regardless. So because "Bonding Jumper" is not in the title or the note, we don't have to run one? What is the rationale of 250.104 sending us to this table?


IMO the title should just say "Grounded Conductor and Bonding Jumpers" and no note would be necessary. Sometimes, less is more.

 

[infinity]

Because a bonding jumper is not listed in the title either... and yet 250.104 sends you to Table 250.102(C)(1) regardless. So because "Bonding Jumper" is not in the title or the note, we don't have to run one? What is the rationale of 250.104 sending us to this table?


IMO the title should just say "Grounded Conductor and Bonding Jumpers" and no note would be necessary. Sometimes, less is more.

I agree completely that it's confusing, all I'm saying it that the 12.5% rule is limited by the note at the bottom.