Table 250.102(C)(1)

[Flapjack]

I have 10 parallel sets of 600 kcmil from a transformer to a switchboard. Looking at note 1 of Table 250.102(C)(1), I would have to take 12.5% of the equivalent area of the parallel set, so I would need a 750 kcmil system bonding jumper. I am getting caught up on the language in note 1 of 250.102(C)(1). Can someone provide an example of when to apply "the grounded conductor or bonding jumper shall not be required to be larger than the largest ungrounded conductor or set of ungrounded conductors"? I don't see how that would ever apply if you are taking 12.5% of an area.

Also the supply side bonding jumper from the transformer to the switchboard only needs to be 1/0 because it is based on each parallel set in each conduit. However, the SSBJ from the switchboard ground bus to the switchboard case would also need to be 750 kcmil for the equivalent parallel sets?

Finally, it is my understanding that since this is a separately derived system, a neutral is not needed and does not need to be brought to the switchboard. In other words, it is compliant to terminate the GEC, SBJ, and SSBJs to the X0 bushing, correct?

 

[infinity]

I have 10 parallel sets of 600 kcmil from a transformer to a switchboard. Looking at note 1 of Table 250.102(C)(1), I would have to take 12.5% of the equivalent area of the parallel set, so I would need a 750 kcmil system bonding jumper. Yes.

I am getting caught up on the language in note 1 of 250.102(C)(1). Can someone provide an example of when to apply "the grounded conductor or bonding jumper shall not be required to be larger than the largest ungrounded conductor or set of ungrounded conductors"? I don't see how that would ever apply if you are taking 12.5% of an area. Good question.

Also the supply side bonding jumper from the transformer to the switchboard only needs to be 1/0 because it is based on each parallel set in each conduit. Yes.

However, the SSBJ from the switchboard ground bus to the switchboard case would also need to be 750 kcmil for the equivalent parallel sets? Where does it say that? Typically the EGC bus is just bolted to the frame of the switchboard by the SWBD manufacturer.

Finally, it is my understanding that since this is a separately derived system, a neutral is not needed and does not need to be brought to the switchboard. In other words, it is compliant to terminate the GEC, SBJ, and SSBJs to the X0 bushing, correct?

I answered within the quote.

 

[Flapjack]

However, the SSBJ from the switchboard ground bus to the switchboard case would also need to be 750 kcmil for the equivalent parallel sets? Where does it say that? Typically the EGC bus is just bolted to the frame of the switchboard by the SWBD manufacturer.

I was basing that off of looking at Exhibit 250.14 which shows a supply-side bonding jumper from the ground bus in the first disconnecting means to the enclosure.

 

[Flapjack]

Can anybody help with the only unanswered question from original post?

Finally, it is my understanding that since this is a separately derived system, a neutral is not needed and does not need to be brought to the switchboard. In other words, it is compliant to terminate the GEC, SBJ, and SSBJs to the X0 bushing, correct?

One additional question I had, was for the system bonding jumper. The feeders have been increased in size to 12 sets of 750 kcmil. 12.5% of the total is 1125. Can the SBJ be split into two 600 kcmil, or must it be one 1250 kcmil?

 

[augie47]

Can anybody help with the only unanswered question from original post?

IMHO, since you are establishing your grounding at the source (transformer) and you have SSBJs to your gear, no grounded conductor is needed.

One additional question I had, was for the system bonding jumper. The feeders have been increased in size to 12 sets of 750 kcmil. 12.5% of the total is 1125. Can the SBJ be split into two 600 kcmil, or must it be one 1250 kcmil?

Good question. I have allowed it but I don't see it addressed directly by the Code.

I'm sure you noted that with the increase in the size of the phase conductors your 1/0 SSBJs are now undersized.

 

[Flapjack]

Yes, I failed to mention that I increased the SSBJs to 2/0.

Thanks for your input!