Contactors: Relay and Coil

Topics: Relay, Electric current, Contactor Pages: 3 (1021 words) Published: November 20, 2010
Contactors & Relays
Contactors and relays are devices that open and close a set or sets of electric contacts by the action of a solenoid coil. A contactor is used to control an electric load in a control system. Contactors make or break a set of contacts that controls the voltage applied to some load in cooling systems. A contactor consists of a coil that opens and closes a set of contacts due to the magnetic attraction created by the coil when it is energized. Magnetic starters are also used to start and stop large loads in cooling systems. The major difference between magnetic starters and contactors is that the magnetic starter houses its own overload. Different manufactures design contactors in different ways, but all accomplish the same purpose which is opening and closing a set of contacts. The armature of a contactor is the portion that moves. The sliding armature mounts between two slots in the frame of the contactors and moves up and down in these slots. The swinging armature is mounted on a pivot or hinge and moves up and down in a swinging motion. The armature of a contactor is connected by a mechanical linkage to a set of contacts that causes a completed circuit when the armature is pulled into the magnetic field produced by the coil. The coil characteristics depend on the type of wire and the manner in which it is wound. Coils are designed to operated on 24volts, 120 volts, 208/240 volts, and 480 volts. Contactors are rated by the ampere draw they can carry. There are two types of loads that contactors can control: and inductive load which has a higher ampere draw on startup than while running; and a resistive load which has a constant ampere draw such as a resistance heater. Contacts are made of silver and cadmium (is a chemical element with the symbol Cd and atomic number 48. The soft, bluish-white metal is chemically similar to the two other metals in group 12, zinc and mercury), which resists sticking. The contacts are...
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