Starting cct. for single-phase async. motors - has protective PTC resistors whose highest temp. triggers supply cct. breaker

摘要

The starting circuit protects a single-phase asynchronous motor main and starting windings during starting from overload if the rotor fails to rotate. A PTC resistor is connected in series with the starting winding across the supply and its increase in resistance protects the winding during the motor starting phase. When the resistor reaches its highest permissible temperature, it operates a thermally triggered circuit breaker which cuts out the supply to both the main and the starting windings. The PTC resistor consists of a flat disc between two electrodes. The circuit breaker lies in thermal contact with one of these electrodes. The whole circuit is conveniently contained in a single housing.