Electrical contactors are used to switch high power in power circuits. Unlike relays, these electrical devices are normally connected directly to the load or current-carrying circuit. Because they also have higher current ratings than relays, electrical contactors are used to control electric motors, lighting and heating systems, capacitor banks, and other electrical loads. Most electrical contactors consist of power contacts, auxiliary contacts, and contact springs; an electromagnet that closes the contacts; and a frame or enclosure that houses the contacts and the electromagnets. High-voltage contactors may also use an inert gas or vacuum around the contacts.
Product specifications for electrical contactors include the number of poles, maximum switching current, maximum switching voltage, and frequency. Poles are the lines or circuits that electrical contactors can make or break. The maximum switching current is usually measured in amps, but may also be given in units ranging from kiloamps to femtoamps. Depending on the whether the device is an AC electrical contactor or a DC electrical contactor, the maximum switching voltage is given either for alternating current (AC) or direct current (DC). Frequency choices for electrical contactors include 50 Hz, 60 Hz, and 400 Hz.
There are several different mounting styles for electrical contactors. Some are integrally mounted on printed circuit boards (PCBs). Others are connected to wiring via standard sockets or plugs. Electrical contactors that mount with brackets, flanges, or DIN rails are also available. DIN is an acronym for Deutsches Institut für Normung, a German national organization for standardization. Typically, DIN rails are used on computer boards. Other unlisted or specialized mounting configurations for electrical contactors are also available.
Electrical contactors differ in terms of available features. Devices with time delays provide delay-on-make, delay-on-break, single-shot, recycling, and interval timing functions. Intrinsically safe (IS) electrical contactors are incapable of releasing sufficient thermal or electrical energy to ignite hazardous atmosphere mixtures even in their most ignited concentration. Electrical contactors with visual indicators provide visual guidance for both power and signal monitoring. Hermetically-sealed devices are designed to prevent contamination and/or the ingress of water. Electrical contactors that latch into position and remain in position until actuated are also available.
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