The Three-Phase Rheostat module consists of three rheostats mounted on a common shaft directly controlled by a single knob on the module faceplate. The rheostats are electrically interconnected in a four-wire wye configuration and each leg is protected from over-current conditions by a thermal-magnetic circuit breaker.

This module is mainly used for speed control of a Three-Phase Wound-Rotor Induction Motor, Model 8505. A limit switch is actuated when the knob of the rheostat is turned fully clockwise, corresponding to maximum resistance. This switch can then be used as an interlock with the Three-Phase Full-Voltage Starter, Model 8521, to make sure that the motor starts with a rotor resistance which provides maximum starting torque.

This module can also be used for other applications where a variable power resistor is needed.