basis of both of these loads. The rating or setting of the overcurrent device must be sufficient to carry the lighting and/or appliance load plus the rating or setting of the motor branch-circuit protective device.
A controller is a device that starts and stops a motor by making and breaking the power current flow to the motor windings. A push-button station, a limit switch, or any other pilot-control device is not considered a controller. Each motor is required to have a suitable controller that can start and stop the motor and perform any other control functions required. A controller must be capable of interrupting the current of the motor under locked-rotor conditions (NEC ® 430-151) and must have a horsepower rating not lower than the rating of the motor, exceptions as permitted.
Branch-circuit fuses or circuit breakers are considered to be acceptable controller devices under the following conditions:
Figure 7-4. - Branch-circuit conductor sizing.
For a stationary motor rated at one-eighth horsepower or less that is normally left running and is constructed so that it cannot be damaged by overload or failure to start.
For a portable motor rated at one-third horsepower or less, the controller may be an attachment plug and receptacle.
The controller may be a general-use switch having an ampere rating at least twice the full-load current rating of a stationary motor rated at 2 horsepower or less and 300 volts or less.
A branch-circuit breaker, rated in amperes only, may be used as a controller. When this circuit breaker is also used for short-circuit and ground-fault and/or overload protection, it will conform to the appropriate provisions of the NEC ® governing the type of protection afforded. Figure 7-5 will help you to understand controller definitions.
Generally, each motor must have its own individual controller. The exception is for motors rated 600 volts or less; a single controller rated at not less than the sum of the horsepower ratings of all of theContinue Reading