It is used for air or catalyzing converter warm-up system, heating system of motor, and also used for power steeling dynamoelectric pump, starter as current switch. Its characters is long life of time, the contact can bear heavy current. It is used for air or catalyzing converter warm-up system, heating system of motor, and also used for power steeling dynamoelectric pump, starter as current switch. Its characters is long life of time, the contact can bear heavy current.