Switching Relays combine clearly labeled PC board layouts with advanced features that allow for total system customization. Whether using basic priority switching or the advanced features of the -EXP controls, the job is made easy. External indicator lights provide instant diagnostic feedback, making a snap of service calls or new installation start-ups. All switching relays are UL and CSA listed, use standard "ice cube" replaceable relays and are compatible with conventional and programmable thermostats.