chapter  12
24 Pages

Relays and Contactors

WithJoseph E. Fleckenstein

Relays of various types are an integral and necessary part of the control and protection of larger electrical gear as transformers, motors, and generators. Reed relays are considered a type of electromechanical device since they contain components that are both electrical and mechanical. Time delay relays are used in control circuits to momentarily postpose a control action. Contactors are available in two-pole, three-pole, and four-pole configurations. Contactors are required in those applications where electrical power must be repeatedly applied and subsequently interrupted. Contactors are also classified as either "general purpose" or "definite purpose." Definite purpose contactors are mostly intended for the original equipment manufacturer market and are to be used in a specific, defined application. Relays and contactors are available with a variety of terminals where conductors may be landed. Some of the more common terminals are the screw type, quick-connect and the pressure type.