Sizing a Supply-Side Bonding Jumper

What is the minimum size supply-side bonding jumper for a service raceway containing 4/0 THHN aluminum conductors?

a) 6 AWG aluminum
b) 4 AWG aluminum
c) 4 AWG copper
d) 3 AWG copper

See answer and applicable Code reference

The correct answer is: c) 4 AWG copper

Article 250 covers the general requirements  for grounding and bonding electrical installations. Part V of this Article focuses on bonding requirements. More specifically, supply-side bonding jumper sizing requirements can be found in Sec. 250.102(C).

As noted in 250.102(C)(1), "The supply-side bonding jumper shall not be smaller than specified in Table 250.102(C)(1)." A quick check of this Table reveals you must use a 4 AWG copper bonding jumper in this situation.


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