NEC: Motors — Part 11

Oct. 4, 2022

Be aware of additional hazards with higher-voltage motors

Article 430, Part XI provides the NEC requirements for motors more than 1,000V. Why this special category? Because there are additional hazards due to the higher voltages [430.221]. Part XI does not substitute for or replace the rest of Article 430. If your motor is more than 1,000V, you apply Article 430 just as if you have a lower-voltage (e.g., 480V) motor — while also applying the amendments and additions in Part XI. For example, a controller must have the marking required 430.8, but also (not instead of) be marked with the control voltage [430.222].

Because of the higher voltage, those flex connections (flexible metal conduit or liquid-tight flexible metal conduit) to the motor terminal box (e.g., weatherhead) can’t be longer than 6 ft [430.223].

Coordinated protection is required with these motors [430.225(A)]. Each motor circuit must have coordinated protection to automatically interrupt overload and fault currents to the motor, the motor-circuit conductors, and the motor control apparatus. An exception exists where the motor is critical to an operation or a greater hazard would exist if the motor is not allowed to operate to failure (an example being a fire pump motor).

The thermal overload protectors for these motors must be integral to the motor or use external current-sensing devices [430.225(B)(1)]. Operation of the overload-interrupting device shall simultaneously disconnect all of the ungrounded conductors [430.225(B)(3)].

You can use either circuit breakers or fuses for fault-current protection. Circuit breakers must be able to be serviced without hazard. Fuses must be arranged so they cannot be serviced while they are energized [430.225(C)(1)]. You cannot use protection devices that automatically reclose the circuit. Obviously, fuses inherently satisfy this requirement.

A single device can provide both overload protection and fault-current protection [430.225(C)(3)].

The ultimate trip current of motor protective devices can’t exceed 115% of the controller’s continuous rating [430.226]. Where branch-circuit disconnecting means is separate from the controller, the current rating of the disconnecting means must be at least that of the ultimate trip setting of the overcurrent relays in the circuit.

About the Author

Mark Lamendola

Mark is an expert in maintenance management, having racked up an impressive track record during his time working in the field. He also has extensive knowledge of, and practical expertise with, the National Electrical Code (NEC). Through his consulting business, he provides articles and training materials on electrical topics, specializing in making difficult subjects easy to understand and focusing on the practical aspects of electrical work.

Prior to starting his own business, Mark served as the Technical Editor on EC&M for six years, worked three years in nuclear maintenance, six years as a contract project engineer/project manager, three years as a systems engineer, and three years in plant maintenance management.

Mark earned an AAS degree from Rock Valley College, a BSEET from Columbia Pacific University, and an MBA from Lake Erie College. He’s also completed several related certifications over the years and even was formerly licensed as a Master Electrician. He is a Senior Member of the IEEE and past Chairman of the Kansas City Chapters of both the IEEE and the IEEE Computer Society. Mark also served as the program director for, a board member of, and webmaster of, the Midwest Chapter of the 7x24 Exchange. He has also held memberships with the following organizations: NETA, NFPA, International Association of Webmasters, and Institute of Certified Professional Managers.