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Industrial Chiller Motor Maintenance

NEC: Air Conditioning and Refrigerating Equipment — Part 2

Dec. 6, 2022
Requirements for the disconnecting means of HVACR hermetic motors

Art. 440, Part 2 provides the requirements for the disconnecting means of the hermetic motors used in HVAC and refrigeration equipment. These disconnects are often accessible to unqualified persons, especially in residential applications. Where that is the case, any enclosure or hinged cover that exposes live parts when open must require a tool to open or be capable of being locked [440.11].

Select the disconnect based on the nameplate rated-load current or branch-circuit selection current (whichever is greater) and the locked rotor current per 440.12(A)(1) and (2). In essence, the ampere rating must be at least 115% of the nameplate rated-load current or branch-circuit selection current (whichever is greater) and you must determine the equivalent horsepower to comply with 430.109.

If the disconnect for a hermetic motor-compressor also supplies other loads, it has what is called a combination load. Determine the ampere rating for the disconnect per 440.12(B)(1). Note that the rating must be at least 115% of the sum of all currents at the rated-load condition determined per 440.12(B)(2).

If the equipment is cord-connected, a separable connector or plug and receptacle can serve as the disconnect [440.13].

Where can you install this disconnect? It must be within sight and readily accessible from the equipment it supplies. This requirement is waived if several conditions are met: it’s in a facility with written safety procedures [Ex 1], and if a plug and receptacle serve as the disconnecting means per 440.13 [Ex 2].

If it can still meet the working space requirements of 110.26(A), it can be installed on or within the HVAC or refrigeration equipment [440.14]. However. you cannot locate it on panels that are designed to permit access to the equipment or where the disconnect would obscure the equipment nameplates [440.14].

When you mount the disconnect, take into consideration how it will be used and how the space around it will be used. This precludes, for example, mounting it with a single No. 10 screw to vinyl siding on a house because it should not move when operated. It also needs to be situated so a technician changing the starting capacitor won’t smack his back on it. Make it readily accessible without putting it in the way. Mount it so the visual aesthetics are preserved. For example, rather than mount it at some random height, mount it at the same height as something else or mount it at some standard height such as 4 ft.

But wait, Art. 440 does not require any of these things, so why do them? Because 110.12 applies to all electrical installations and requires you to install electrical equipment in a professional and skillful manner. While the wording is, on its face, open to wide interpretation, it’s also true that any qualified person understands the intended meaning due to training and experience. It’s never good to see what you can get by with; it’s always good to “sign” your work with solid workmanship.

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.

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