The contactor is an electronically controlled switch for switching the power supply circuit. Contactors are typically controlled by circuitry having a much lower power level than the switching circuitry, such as a 24 volt coil electromagnet that controls a 230 volt motor switch.
Unlike general purpose relays, contactors are designed to be directly connected to high current load devices. Relays tend to have low capacity and are typically designed for normally closed and normally open applications. Devices that switch more than 15 amps or that have a power rating in excess of a few kilowatts are often referred to as contactors. In addition to the optional auxiliary low current contacts, the contactors are almost always equipped with normally open ("A") contacts. Unlike relays, contactors are designed to control and suppress arcing that occurs when heavy motor current is interrupted.
Contactors come in many forms and have different capacities and functions. Unlike circuit breakers, contactors are not used to interrupt short-circuit currents. Contactors range from a few amps of breaking current to thousands of amps and 24 volts to many kilovolts of contactors. The physical dimensions of the contactor range from small enough to pick up the device with one hand to a large device of approximately one meter (code).
Contactors are used to control motors, lighting, heating, capacitor banks, thermal evaporators and other electrical loads.