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.
About the Author
Mike Holt
Mike Holt is the owner of Mike Holt Enterprises (www.MikeHolt.com), one of the largest electrical publishers in the United States. He earned a master's degree in the Business Administration Program (MBA) from the University of Miami. He earned his reputation as a National Electrical Code (NEC) expert by working his way up through the electrical trade. Formally a construction editor for two different trade publications, Mike started his career as an apprentice electrician and eventually became a master electrician, an electrical inspector, a contractor, and an educator. Mike has taught more than 1,000 classes on 30 different electrical-related subjects — ranging from alarm installations to exam preparation and voltage drop calculations. He continues to produce seminars, videos, books, and online training for the trade as well as contribute monthly Code content to EC&M magazine.