Code Q&A

July 22, 2005
Q. How would you size the bonding wire to a motor that’s protected by an inverse time circuit breaker? A. The equipment grounding (bonding) conductor must be sized in accordance with Table 250.122, based on the ampere rating of the circuit-protection ...

Q. How would you size the bonding wire to a motor that’s protected by an inverse time circuit breaker?

A. The equipment grounding (bonding) conductor must be sized in accordance with Table 250.122, based on the ampere rating of the circuit-protection device, but in no case is it required to be larger than the circuit conductors.

For example, a 5-hp, 208V, 3-phase motor with an FLC of 16.7A, and that’s wired with 12 AWG [430.22(A)], with a 40A short-circuit, ground-fault protection device [430.52(C)(1)] would have a 12 AWG equipment grounding (bonding) conductor. Since the circuit wires are 12 AWG, there is no reason to install a 10 AWG equipment grounding (bonding) conductor. Please review requirement in 250.122, which in part states "equipment grounding conductors shall not be smaller than shown in Table 250.122 but shall not be required to be larger than the circuit conductors supplying the equipment."

Got a question for Mike? E-mail him at [email protected].

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.

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