rokefuller
Member
In a recent continuing education class on grounding, one activity was to size individual bonding jumpers to each of three parallel Supply side conduits each containing 500kcmil service entrance cables for a three phase 208/120 service. (phase and voltage deduced for blk, red, blu, and wht conductors on the diagram) Part two of the activity was to size "the bonding jumper to all three conduits if a single bonding jumper is installed in a daisy-chain manner (assumed)".
The answer for part two on the answer sheet reads:
2. 250.102(C) applies. Since the area of the three service entrance conductors exceeds 1100 kcmil (Table 250.66 maximum), a single bonding jumper must not be smaller than 12.5% of the area of the service-entrance conductors: 500kcmil X 3 = 1500 kcmil X .125 = 187,500 cm. Table 8 of Chapter 9 shows a 4/0 conductor (211,600 cm) to be the next larger size
My contention was that the language of 250.102 did not fit the answer given. The 12.5% rule appears to apply to one conduit containing one set of service entrance conductors larger than 1100kcmil. The language of the second half referrs to paralleled conductors. "The size of the bonding jumper for each raceway or cable shall be based on the size of the service-entrance conductors in each raceway or cable.
I can not see in the language of this section of code any support for daisy chaining a single conductor between parallel conduits as a bonding jumper on the supply side of a service. Is the intent of the code here to limit the bonding of parallel conduits on the supply side to individual jumpers for each conduit? Is there another section which I have missed which supports the answer sheet's version of sizing the bonding jumper?
The answer for part two on the answer sheet reads:
2. 250.102(C) applies. Since the area of the three service entrance conductors exceeds 1100 kcmil (Table 250.66 maximum), a single bonding jumper must not be smaller than 12.5% of the area of the service-entrance conductors: 500kcmil X 3 = 1500 kcmil X .125 = 187,500 cm. Table 8 of Chapter 9 shows a 4/0 conductor (211,600 cm) to be the next larger size
My contention was that the language of 250.102 did not fit the answer given. The 12.5% rule appears to apply to one conduit containing one set of service entrance conductors larger than 1100kcmil. The language of the second half referrs to paralleled conductors. "The size of the bonding jumper for each raceway or cable shall be based on the size of the service-entrance conductors in each raceway or cable.
I can not see in the language of this section of code any support for daisy chaining a single conductor between parallel conduits as a bonding jumper on the supply side of a service. Is the intent of the code here to limit the bonding of parallel conduits on the supply side to individual jumpers for each conduit? Is there another section which I have missed which supports the answer sheet's version of sizing the bonding jumper?
