The optoisolated series of relays may be used when the controller does not have sufficient coil drive power available to energize a relay of the desired contact rating. The power to energize the relay can be brought to the relay on a separate pair of wires along with the control output of the controller, or can be a local power source near the relay. 

The voltage output of the controller is used to turn on an optoisolator that connects the power source to the coil of the relay. The optoisolator isolates the Class 2 output of the controller from potential feedback and voltage transients. Using this approach, an LED output, or low current analog output, of a controller can be used to control up to a double pole 20 Amp relay with a 3 horsepower rating. Optoisolated relays are available in T and Panel style. 

Enclosed Relay Hi/Low Separation 20 Amp SPDT, 208-277 Vac Power Input + 5-25 Vac/dc Control Input