How2Day: The Parts of a Contactor

Contactors are key to electrical production. Electric image by Fenia from Fotolia.com
A contactor is a relay that is used to control amounts of power between the individual contacts of an electrical device. Constructed of many contacts, it generally is open to allow for power to load into the coil so that it can be re-energized. Most commonly seen in electrical motors, a contactor is constructed of six basic sections, each of which has individual parts.

Constructed of the mounting plate, base, stationary contacts and arc hood, the main section provides the base from which the other sections operate. The mounting plate allows the contactor to be mounted to an electrical panel. The base, generally constructed of plastic, is the mounting point for the stationary contacts and other parts. The arc hood is largely protective, keeping the contacts covered in case of an electrical arc.

Including the contact carrier, movable contacts, armature and retainer springs, the second section allows the coils to stay energized. More important, these parts ensure the ability of the "armature to move the movable set of contacts against the stationary contacts when the coil is energized," according to the Industrial Electronics Information for Manufacturing Applications website. When the magnetic field of the coil is energized, the armature moves, while the retainer springs keeps the other parts stationary within the contactor.

Including the head cover and arc quencher, the third section is integral to ensuring no damage occurs. In containing electrical arcs that may occur, the head cover and arc quencher ensure that the contacts and nearby electrical components aren't damaged when the contacts open and close.

The coil, the fourth major part of the contactor, is rated on circuit voltage from low to high. It is rectangular with two holes that allow space for the magnet yoke, and 2 feet of the yoke must be in contact with the armature as it closes.

Generally constructed of laminated steel to prevent it from maintaining magnetism after the coil de-energizes, the magnet yoke must project from the center of the coil. The yoke retainer helps to ensure that the yoke stays in the correct position. Both parts are removable.

The final part of a contactor is the coil cover, which in addition to covering the coils allows for additional space to attach auxiliary contacts.. Non-auxiliary contacts are generally included in the contactor to hold or seal the existing contacts. Connected with the start button, these contacts close the coil once they have become re-energized.

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