contactors

A contactor is an electrically controlled switch used to make or break a high-current power circuit. It is energized by a control circuit and designed for frequent operation, typically handling motors, pumps, heaters, and other heavy loads. Contactors differ from small relays mainly in their higher current ratings and duty.

Construction and operation: A contactor comprises a magnetic coil and one or more poles with main contacts, plus optional auxiliary contacts. Energizing the coil attracts the contacts to close the main circuit; de-energizing releases them to open. Pole counts vary (1–4) and configurations include normally open, normally closed, or mixed. Coils are rated for AC or DC, and many types include arc suppression. In motor systems, contactors are often paired with overload relays to form a motor starter.

Applications and standards: Contactors control motors, pumps, conveyors, HVAC, and other loads in industrial and commercial settings. They are specified by standards such as IEC 60947-4-1 for AC/DC contactors and IEC 60947-5-1 for accessories; in North America, UL 508 applies. Coil voltages range from low (12–24 V) to line voltage (120–480 V AC); main contact ratings span from a few amperes to thousands.

Maintenance and selection: Selection considers load current, voltage, starting current, and duty cycle. Contacts wear from arcing and require periodic inspection and replacement. Coils can fail and spare units or coils are common. When used with overload devices, contactors form standard motor starters.