Brush up on what the NEC says about air conditioning

During the hottest parts of the summer, most people do not notice the sound of air conditioning units turning on and off, but if a unit fails to start, the effect is noticed immediately. Comfort becomes a premium to be restored at all costs. However, the heat of the moment should not sacrifice safety and the rules in the National Electrical Code governing air conditioning must be followed.

An understanding of the basic concept of Article 440 covering air conditioning (AC unit) and refrigeration equipment with its relationship to other articles in the NEC is a must before installing or maintaining the equipment. The scope of Article 440 provides necessary and critical information about the application and overall coverage of equipment under this category.

Article 440 applies to electric motor-driven air-conditioning and refrigerating equipment, as well as to the branch circuits and controllers necessary to provide power to this equipment. This article provides special considerations for individual branch circuits specifically supplying hermetic refrigerant motor-compressors and for any circuit where air-conditioning or refrigerating motor-compressor equipment is connected.

Many contractors and installers may not have taken the time to read the information provided in Section 440.3 and just assume that Article 440 is the sole article dealing with air-conditioning and refrigerating equipment. In fact, Article 440 is merely an extension of Article 430 covering motors, motor circuits, and motor controllers. Section 440.3(A) states that the provisions in Article 440 are in addition to or may amend the provisions in Article 430 and other articles of the NEC.

However, many may miss the fact that Article 440 only applies to hermetic refrigerant motor compressor equipment, as evidenced by the information contained in 440.3(B). Section 440.3(B) requires compliance with the rules in Articles 422 for appliances, Article 424 for fixed electric space heating, or Article 430 for motors where this equipment does not contain a hermetic refrigerant motor compressor. Refrigeration compressors driven by conventional motors, furnaces with air-conditioner evaporator coils installed, fan coil units, remote commercial refrigerators and numerous other equipment are covered by Articles 422, 424 or 430, not Article 440.

Furthermore, Section 440.3(C) very specifically requires room air-conditioners, household refrigerators, household freezers, drinking water coolers and beverage dispensers, all of which contain hermetic compressors, to be considered as appliances and thus requiring compliance with Article 422, as well as Article 440. In addition, any hermetic motor-compressors, their accessories, circuits, controllers and related equipment must comply with the requirements in the appropriate articles for hazardous (classified) locations, and motion picture or television studios, where installed in such locations.

Where capacitors are used with the air-conditioning or refrigerating equipment, compliance with Section 460.9 is necessary since the addition of capacitors to the motor circuit may affect the rating or setting of the motor overload device protecting the motor, depending upon where the capacitor is installed in the circuit. Often, a hard start kit, consisting of capacitors and other related components which are added to the circuit to improve the power factor of the motors, is installed on air-conditioning units where wear and aging of the motors have caused increased starting current. Care should be taken so the placement of these devices does not affect the rating or setting of the motor overload device and proper overload protection is maintained.

The rated load current for a hermetic refrigerant motor-compressor is the rated current resulting when the motor-compressor is operated at its rated load, rated voltage, and rated frequency. This rated load current marking on the nameplate of the unit will provide the installer or service personnel with information necessary to determine whether the unit is operating within the proper manufacturer’s rating of the unit.

The nameplate will often contain the maximum branch circuit selection current of the unit. This is the value in amperes provided by the manufacturer of the unit that is used in place of the rated load current in determining the ratings of motor branch-circuit conductors, the disconnecting means, controllers, and any branch-circuit short-circuit and ground-fault protective device. Since most of these units have factory-installed overload devices, this makes sizing of the protective devices and the branch circuit components relatively easy.

Most air-conditioning and refrigerating units consisting of compressors and multiple fan motors will be factory marked with a nameplate containing the manufacturer’s name, trademark or other identifying symbol; phase, voltage and frequency; as well as the rated load current in amperes and the maximum rating of the branch circuit short-circuit and ground-fault protective device.

Care should be taken not to exceed the ratings permitted by the nameplate, unless conditions are such to warrant a higher value, such as in a very high ambient temperature location or other adverse conditions, and then only based on specific permission given in the NEC. EC

ODE is a staff engineering associate at Underwriters Laboratories Inc., in Research Triangle Park, N.C. He can be reached at 919.549.1726 or at


About the Author

Mark C. Ode

Fire/Life Safety Columnist and Code Contributor
Mark C. Ode is a lead engineering associate for Energy & Power Technologies at Underwriters Laboratories Inc. and can be reached at 919.949.2576 and .

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