Maintenance, Repair & Operations

NEC: Air Conditioning and Refrigerating Equipment, Part 4

Feb. 7, 2023

Learn about the requirements in Art. 440, Part 4.

Article 440, Part 4 provides the requirements for the circuit conductors used in HVAC and refrigeration equipment. For other kinds of installations, you must specify the ampacities of motor conductors per Part III of Article 310. You do that with hermetic motors also, except as modified by 440.6(A), Exception No.1 [440.31]. And what does that Exception say?

“Where so marked, the branch-circuit selection current shall be used instead of the rated-load current to determine the…ampacity of…the branch circuit conductors.”

For a single motor compressor, the branch-circuit conductor ampacity must be at least 125% of the motor-compressor rated-load current or the branch-circuit selection current — whichever is greater.

If you have a wye-start, delta-run connected motor-compressor, you can base the selection of the branch-circuit conductors between the motor and the controller on 72% (rather than 125%) in the above calculations.

For conductors supplying multiple motor-compressor loads, the conductor ampacity must be at least as much as the sum of these quantities [440.33]:

The sum of the rated-load current or branch-circuit selection current (whichever is greater).
The sum of the full-load current rating of all other motors.
25% of the highest motor-compressor or motor full load current in the group.

There’s an exception that applies if the circuitry has an interlock to prevent a second unit or group from starting and running.

Conductors that supply compressor load(s) plus non-compressor loads must have an ampacity sufficient for the sum of [440.34]:

Those additional loads.
The compressor loads as determined in 440.33.

Conductors that supply multimotor and combination-load equipment must have an amapacity at least that of the minimum circuit ampacity marked on the equipment per 440.4(B) [440.35].

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.