The Basic HVAC/R Relay

This figure shows a typical pilot-duty relay. A pilot-duty relay usually controls less than 2 amps of current at its contacts. Some relays, however, have more than one set of contacts. As you can see in the figure, there are four basic parts to the relay. The coil of wire becomes magnetized when a voltage or current is applied to it. The armature is connected to the contacts. (Generally, the armature and the contacts are electrically isolated from one another.) The spring keeps the relay in its normally open or normally closed position when no power is applied.

EXCERPT FROM TECHNICAL INSTITUTE MANUAL #2, available from the online store at RSES (Refrigeration Service Engineers Society), the HVAC/R Training Authority.

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