Code Q&A: How to Determine the Highest Rated Motor in a Group

Sept. 1, 2020

Test your NEC knowledge.

Q. When the NEC refers to the highest rated motor on a circuit with multiple motors, how is the largest motor of the group determined?

See answer below.

A. When sizing motor circuit conductors, the highest rated motor is the motor with the highest rated full-load current (FLC) rating [Sec. 430.17].

Example: Which of the following motors has the highest FLC rating?

A good method to determine the highest rated motor is to draw out the motor circuit as follows (Figure):

10 hp = 30.80A [Table 430.250]
5 hp = 30.80A [Table 430.248]
3 hp = 34.00A [Table 430.248]

Answer: As you can see, the 3 hp, single-phase, 120V motor has the highest FLC rating.

These materials are provided to us by Mike Holt Enterprises in Leesburg, Fla. To view Code training materials offered by this company, visit www.mikeholt.com/code.

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.