Sizing the Supply-Side Bonding Jumper

The supply-side bonding jumper on the supply side of services shall be sized according to the _____.

a) overcurrent device rating
b) ungrounded supply conductor size
c) service drop size
d) load to be served

See answer and applicable Code reference

The correct answer is: b) ungrounded supply conductor size

Section 250.102 of the 2011 NEC covers the requirements for bonding conductors and jumpers. As noted in 250.102(C)(1), "The supply-side bonding jumper shall not be smaller than the sizes shown in Table 250.66 for grounding electrode conductors. Where the ungrounded supply conductors are larger than 1,100 kcmil copper or 1,750 kcmil aluminum, the supply-side bonding jumper shall have an area not less than 12.5% of the area of the largest set of ungrounded supply conductors."