Contactors are used to switch high power in electrical circuits. They provide the machanical connection (power switch) between the circuit breaker and the motor. Their job is to connect and remove power to the motor when required. Because this type of mechanical unit can weld in under certain conditions it is normal for two units to be used in series in safety related circuits. These contactors are maufactured to the highest standards. They have acheived and maintained the high standards required by the american UL standards. All units carry the UL and CE marks and have full RoHs documentation.