A relay is an electromagnetic device, which is used for closing or opening of an electrical circuit. The relay may be classified as Shelf type and Plug-In-Type

Plug-in-type relays which are plugged in to prewired terminal boards. It works on electromagnetic principle. Each relay has a base electromagnet, armature, contact spring, contacts, transparent cover, and handle. A non-magnetic residual pin is fixed on the inner face of armature, in all relay except magnetic latch relays.

The relays covered by this specification are for use in line circuits where alternating current at industrial frequency my be present in the circuit.

This specification relates to design requirements for A.C. immune miniature atractive armature D.C. neutral line relays of the plug-in type for use in railway signaling circuits.