The Tandem Rheostats comprises two rheostats mounted on a common shaft directly controlled by a single knob on the module faceplate. This allows simultaneous and equal variations in resistance in both legs. Each rheostat is protected from over-current conditions by a thermal-magnetic circuit breaker.

The main use of this module is in a Ward Leonard system for speed control of a DC Motor, Model 8211, whereby the speed and direction of rotation can be changed. In this application the Tandem Rheostats are used to control the shunt field current of a dc generator, which in turn drives a dc motor. However, since the rheostats are not interconnected, they can be used in applications where one or two stand-alone rheostats are needed.