Safety in operation and maintenance dictates that all motor-operated equipment have a means of fully disconnecting the power supply. This is a requirement of National Electrical Code (NEC) and Occupational Safety and Health Administration (OSHA) regulations. The NEC includes requirements for disconnecting means for the motor itself and for the motor controller; both sets of requirements must be satisfied.
Disconnecting means usually consist of an enclosed safety switch or circuit breaker with an external operating handle. Like motor contactors, switches and circuit breakers used in motor circuits must be capable of making and breaking motor locked-rotor current in addition to continuously carrying full-load current. Consequently, these devices carry horsepower ratings as well as continuous current ratings, and both must equal or exceed the corresponding motor ratings for a safe application.