Re: Supply Side Bonding
Thank you for your replies. Still uncertain however, I contacted the NFPA for clarification.
Basically, the method used to determine the size of the bonding jumper is dependant on whether the bonding jumper itself will be installed as a single conductor or paralleled. My original question specified that the service conductors were parallelled but I did not address how the bonding jumper would be installed. Apparently, this makes a difference.
Thanks again. Here's the "unofficial" NFPA response.
Dave:
Section 250.102 provides the rule for Equipment Bonding Jumpers. 250.102(A) gives the material type and method. 250.102(C) provides the rule for sizing the conductor(s)on the supply side of the service.
Sizing is done based on the cumulative amount of the service entrance conductors. Up to and including 1100 kcmil copper and 1750kcmil AL, the size is based on Table 250.66. If all phase conductors when added together exceed those defined values in 250.66, then the total amount is multiplied by 12.5%.
For example: 4 sets of 500 kcmil copper conductors are used for a service. This means 2,000,000 cir mils for A, and B and C phase. 2,000,000 X 12.5% is 250,000 cir mils for a single bonding conductor connected to each conduit end and then connected to the grounded conductor terminal bar.
You are also allowed to use 4 individual conductors, based on the size of the phase conductors in each conduit raceway. In this type of application, 500 falls between 350--600 kcmil. This requires you to use one 1/0 copper conductor, and connect it to each of the four separate raceways, the other end connected to the grounded conductor terminal bar.
In summary, the answer to your question is yes for both methods. Neither method is wrong, one could simply be easier to work with in small confined enclosures. I hope this satisfies your questions and concerns.