Contactor

A contactor, sometimes spelled contator in older or regional usage, is an electrically controlled switch designed to switch an electrical power circuit. It is used to control large amounts of current with a relatively small control signal, typically from a control circuit or automation system. Contactors are commonly employed to control motors, lighting, heating, and other heavy electrical loads. They differ from relays primarily in their higher current ratings and robust construction for frequent switching.

A contactor consists of a coil or coil assembly that, when energized, creates a magnetic field that pulls in a set of main contacts, closing the circuit. When de-energized, built-in springs return the contacts to their normally open or normally closed positions. In addition to the main power contacts, contactors often include auxiliary contacts used for control or signaling circuits. Contactors are categorized by the number of poles (e.g., 2P, 3P, 4P), and by contact configuration (normally open NO, normally closed NC, or mixed).

Electrical characteristics include coil voltage (AC or DC), and the capacity of the main contacts, expressed as current rating and voltage rating. They may feature arc suppression devices, such as RC snubbers or varistors, and can be supplied with motor overload protection as part of a motor starter assembly. Coil suppression helps protect control electronics from voltage spikes. Modes of operation include non-latching and latching types; latching contactors hold their position after the coil is de-energized, often requiring a reverse pulse to release.

Selection considerations include rated current and voltage, coil voltage, operating duty, mechanical life, enclosure type, and the specific load and control requirements. Regular maintenance focuses on contact wear, alignment, and cleaning to prevent arcing and contact sticking.