Functional Devices RIBU1C Pilot Relay, 10 Amp SPDT, 10-30 Vac/dc/120 Vac Coil, NEMA 1 Housing

This is a very useful device which allows one circuit to control another. The first circuit is either 120V or 24V (your choice) and if energized, current flows through a control coil. This control coil operates a set of contacts. They act as on/off switches for the second circuit. One switch is Normally Open (NO), the other Normally Closed (NC). When energized, NO switch shuts, NC opens. You can use one or both, depending on your application.My application was the addition of an in-line HVAC duct booster fan. I wanted the fan to operate only when the HVAC unit was operating. So I chose the NO switch. This relay provided the means to make it happen. My hand drawn wiring diagram is attached to show how I set it up.

Perfect for controlling a light...