Abstract: Apparatus for preventing damage to resistor grids in the propulsion controller circuit of a direct current motor, particularly of the type used in driving railway vehicles, in which a line breaker relay is de-energized whenever the propulsion controller fails to progress from the switch position to the full series position within 15-25 seconds. The line breaker relay remains de-energized for the duration of the power cycle of the propulsion controller and becomes operational automatically after the master control handle is returned to the off position.

Abstract: Apparatus for preventing overvoltage and overcurrent damage to direct current motors, and wheel lockout in electrically powered vehicles having dynamic and mechanical brake assemblies includes dynamic braking voltage and current sensing circuits, a first network responsive to detected dynamic braking voltages exceeding a predetermined value, a second network responsive to dynamic braking currents exceeding a predetermined level, and a third network responsive to dynamic braking current exceeding a different predetermined level at the same time that excessive mechanical braking occurs and for providing an output when such conditions coexist for more than a predetermined time period, and an interrupting circuit responsive to outputs from the first, second, and third networks for interrupting dynamic braking and substituting therefor mechanical braking.