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An example of a contactor with an exploded-view picture is shown Ill. 1. From this figure notice that the contactor has six basic parts. The main section of the contactor consists of mounting plate, base, stationary contacts, and arc hood. The mounting plate provides a means of mounting the contactor in an electrical panel. The base is made of plastic and provides mounting points for the stationary contacts and the remainder of the contactor's moving parts. The arc hood provides a cover for the contacts so that any electrical arc that may occur is contained.
The second section of the contactor includes the contact carrier, movable contacts, armature, and retainer spring. These parts provide the apparatus that allows the armature to move the movable set of contacts against the stationary contacts when the coil is energized. The armature is the part of the contactor that actually moves when the magnetic field in the coil is energized, and the retainer springs keep these parts in place.
The third section of the contactor is the head cover and arc quencher. These parts contain the arc that occurs when the contacts open or close so it can't cause damage to the contacts or the electrical components mounted near the contactor.
The fourth part of the contactor is the coil. The coil is manufactured in a rectangular shape with two square holes in it. These holes provide a space for the magnet yoke to protrude through so that the two feet of the yoke can make contact with the armature when the armature moves to the closed position. Notice that the yoke is made of laminated steel so that it doesn't retain the residual magnetism when the coil is de-energized.
The fifth section of the contactor includes the magnet yoke and the yoke retainer. The yoke is mounted so that it protrudes through the middle of the coil. The retainer keeps the yoke in position, and it's removable so that the yoke can be removed, which allows the coil to be removed. The yoke actually helps to keep the coil in its proper position.
The sixth part of the contactor is the coil cover. The coil cover also provides a place to mount any additional auxiliary contacts. One set of NO auxiliary contacts is usually provided to serve as hold-in or seal-in contacts for the contactor. The hold-in contacts are connected in parallel with the start push button so that when the start button is momentarily depressed and released, the hold-in contacts will close when the coil is energized to provide an alternate path around the start push button contacts. The current rating for the auxiliary contacts is usually very small because they only need to carry current that's used to energize the coil.
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