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AC contactor for pump application. A contactor is an electrically controlled switch used for switching an electrical power circuit. [1] A contactor is typically controlled by a circuit which has a much lower power level than the switched circuit, such as a 24-volt coil electromagnet controlling a 230-volt motor switch.
When a pair of contacts touch, they can pass an electrical current with a certain contact resistance, dependent on surface structure, surface chemistry and contact time; [2] when the pair is separated by an insulating gap, then the pair does not pass a current.
They are used as high-current switches or contactors, where contact erosion from constant cycling would be a problem for conventional relay contacts. Owing to environmental considerations about the toxicity of mercury, mercury relays are mostly obsolete, though modern encapsulated units still have applications.
Plasma contactors are devices used on spacecraft in order to prevent accumulation of electrostatic charge through the expulsion of plasma (often Xenon). An electrical contactor is an electrically controlled switch which closes a power or high voltage electrical circuit .
Continuous current ratings for common contactors range from 10 amps to several hundred amps. High-current contacts are made with alloys containing silver. The unavoidable arcing causes the contacts to oxidize; however, silver oxide is still a good conductor. [22] Contactors with overload protection devices are often used to start motors. [23]
A magnetic starter has a contactor and an overload relay, which will open the control voltage to the starter coil if it detects an overload on a motor. [1] [2] The overload relay opens a set of contacts that are wired in series with the supply to the contactor feeding the motor.
The work can be done, for example, by generators, (electrochemical cells) or thermocouples generating an electromotive force. Electric field work is formally equivalent to work by other force fields in physics, [1] and the formalism for electrical work is identical to that of mechanical work.
The development of the varistor, in form of a new type of rectifier based on a cuprous oxide (Cu 2 O) layer on copper, originated in the work by L.O. Grondahl and P.H. Geiger in 1927. [3] The copper-oxide varistor exhibited a varying resistance in dependence on the polarity and magnitude of applied voltage. [4]