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.
MOTOR CONTROLLER PROTECTION
(NEC® 430, PART G)
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 the