Magnetic contactors

A contactor is an electrical device that can switch ON and OFF an electrical load e.g. an electrical motor, upon an electrical command from another system e.g. a PLC. They are used when a motor load needs to be switched often and for long periods of time without maintenance. Contactors electrical endurance ranges from a few 100,000 to a few million open-close cycles without maintenance. Contactors are typically selected base on their rated current or power (kW or HP), by the control voltage used to operate their coil (e.g. 24Vdc, 120Vac, 240Vac), the frequency that coil can operate at (50/60Hz), the number (2, 3 or 4 poles) and layout of poles (e.g. 1NO+3NC, 2NO+2NC, 3NO+1NC). In order to achieve specific control function e.g. electrical latching, emergency stop, etc. Contactors also often come pre-equipped with auxiliary contacts.

Contactors are always a better choice than any other switching device to switch motors because they allow centralization of control with very minimal wiring. Contactors are also very tolerant to high inrush currents increasingly happening in today's high efficiency motors.

Contactors are installed upstream the motor usually in a control cabinet on or near the motor or in a motor control center (MCC).