Motors, Motor Circuits and Controllers, Part II: Article 430

CIF figure 1

Requirements for motors, motor components and controllers can be found in a number of articles in the National Electrical Code (NEC), but Article 430 specifically covers motors, motor branch-circuit and feeder conductors and their protection, motor overload protection, motor control circuits, motor controllers and motor control centers (MCCs) [430.1].

While some terms pertaining to motors are defined in 430.2, Article 100 defines other motor terms and states the reason for this in its scope. In general, Article 100 defines terms used in two or more articles only.

Article 100 defines these seven terms pertaining to motors: adjustable speed drive, adjustable speed drives system, control circuit, motor control center, motor-control switch, thermal protector (as applied to motors) and thermally protected (as applied to motors). Article 430 does not define these terms because they are used in at least one additional article. As Article 100 defines, an MCC is an assembly of one or more enclosed sections having a common power bus and principally containing motor control units (see Figure 1).

Figure 1: Motor Control Center

Article 430 defines four terms pertaining to motors: “controller,” “part-winding motors,” “system isolation equipment,” and “valve actuator motor (VAM) assemblies.”

It is interesting that both Article 100 and 430 define “controller.” In Article 100, controller is defined as a device or group of devices that serves to govern, in some predetermined manner, the electric power delivered to the apparatus to which it is connected. “Controller” is in the Code more than 500 times. When used in Article 430, the definition in 430.2 is applicable. For the purpose of Article 430, a controller is any switch or device that is normally used to start and stop a motor by making and breaking the motor circuit current [430.2].

Instead of just using the term “controller,” the Code also uses the term “motor controller.” The definition of “controller” in 430.2 is also applicable to “motor controller.” While the NEC uses the terms “controller” or “motor controller,” the term used in the field is usually “starter” or “motor starter.”

Requirements for motor controllers are in Article 430, Part VII; the relevant sections are 430.81 through 430.90. In accordance with 430.82(C), a motor controller for stationary motors rated 2 horsepower (hp) or less and 300 volts (V) or less, can be a general-use switch or a general-use snap switch under certain conditions. Per Article 100, a general-use switch is intended for use in general distribution and branch circuits. It is rated in amperes (A) and is capable of interrupting its rated current at its rated voltage. In the field, a general-use switch is usually called a “disconnect,” “disconnect switch” or a “safety switch.” Article 100 defines general-use snap switches as a form of general-use switches constructed so they can be installed in device boxes or on box covers or otherwise used in conjunction with wiring systems recognized by the NEC. Requirements for both types of switches are in Article 404.

When a general-use switch or a general-use snap switch is installed as a motor controller, it must have an ampere rating, as 430.82(C) specifies. For certain motors, a motor controller can be a general-use switch (disconnect) if the disconnect has an ampere rating at least twice the full-load current (FLC) rating of the motor [430.82(C)(1)].

For example, a disconnect or safety switch will be installed as a motor controller for a stationary motors rated 2 hp or less and 300V or less. This disconnect will have an ampere rating of 30A. The maximum motor FLC permitted on this disconnect is 15A (30 ÷ 2 = 15).

For certain motors on alternating current (AC) circuits, a motor controller can also be a general-use snap switch if the switch is suitable only for use on AC (not general-use AC/DC snap switches) and if the motor FLC rating is not more than 80 percent of the switch’s ampere rating [430.82(C)(2)].

For example, a general-use, AC snap switch will be installed as a motor controller for a stationary motor rated 2 hp or less and 300V or less. This general-use, AC snap switch will have an ampere rating of 20A. The maximum motor FLC permitted on this switch is 16A (20 × 80 percent = 16) (see Figure 2).

Figure 2: General-Use Switch and General-Use Snap Switch

Motor controllers can also be motor starters, combination motor starters, manual motor starters, inverse time circuit breakers and molded case switches. A motor controller shall have a rating as 430.83(A) specifies, unless otherwise permitted in 430.83(B) or (C) or as specified in (D), under the defined conditions. As 430.83(A)(1) states, controllers, other than inverse time circuit breakers and molded case switches, shall have horsepower ratings at the application voltage not lower than the motor’s horsepower.

Some motor starters have a switch such as a disconnect switch. Article 100 defines a “motor-circuit switch” as a switch rated in horsepower that is capable of interrupting the maximum operating overload current of a motor of the same horsepower rating as the switch at the rated voltage. In accordance with 404.13(D), motor-circuit switches shall be permitted to be of the knife-switch type (see Figure 3).

Figure 3: Motor Controllers

An industrial control panel is a piece of equipment used quite often with motors. As Article 100 defines, an industrial control panel is an assembly of two or more components consisting of one of the following: (1) power circuit components only, such as motor controllers, overload relays, fused disconnect switches and circuit breakers; (2) control circuit components only, such as push buttons, pilot lights, selector switches, timers, switches and control relays; (3) a combination of power and control circuit components. These components, with associated wiring and terminals, are mounted on, or contained within, an enclosure or mounted on a subpanel.

The definition continues by stating the industrial control panel does not include the controlled equipment. While industrial control panels may contain equipment (such as motor controllers) that are referenced in Article 430, the industrial control panel itself is not referenced in Article 430. Article 409 covers industrial control panels intended for general use and operating at 1,000V or less (see Figure 4).

Figure 4: Industrial Control Panel

Certain motors and controllers not only have to comply with the applicable provisions in Article 430, but they also have to comply with applicable provisions from another article. Table 430.5 is helpful in determining if it will be necessary to look for additional requirements in another article because of the type of motor, the motor equipment or the type of occupancy.

For example, an air conditioning unit will be installed outside. This unit will have a motor compressor and a condenser fan motor. To see if it is necessary to look in another article for additional provisions, examine Table 430.5. The top line in Table 430.5 shows air conditioning and refrigerating equipment shall comply with applicable provisions in Article 440. Therefore, motors in air conditioning and refrigerating equipment have to comply with the applicable provisions in Article 430 and Article 440. The provisions of Article 440 apply to electric motor-driven air conditioning and refrigerating equipment and to the branch circuits and controllers for such equipment.

Article 440 also provides for the special considerations for circuits supplying hermetic refrigerant motor-compressors and for any air-conditioning or refrigerating equipment that is supplied from a branch circuit that supplies a hermetic refrigerant motor-compressor.

Next month’s column continues the discussion of requirements for motors, motor circuits and controllers.

About the Author

Charles R. Miller

Code Contributor
Charles R. Miller, owner of Lighthouse Educational Services, teaches classes and seminars on the electrical industry. He is the author of “Illustrated Guide to the National Electrical Code” and NFPA’s “Electrical Reference.” He can be reached at 615....

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