Relay panels are typically mounted next to the electrical circuit breaker panels. The circuit breaker panel feeds into the relay panel, with the relays within the panel acting as a switching device for the circuit. Many relay panels can be fed by both 120V and 277V circuit breaker panels, and relay groups can be fed by different voltages within the same panel. Each relay can be individually programmed through the system controller or the relay panel.
The relay panels provide line voltage control of the lighting loads. Relay panels allow for a single circuit to feed into several relays, and allow multiple circuit breaker panels to feed into a single relay panel. While relay panels can be programmed or controlled by a system controller, they can also operate without the system controller. The relay panels typically have status indicators for the relay outputs, dry contact inputs for program override purposes, and inputs for monitoring devices, such as photocells and occupancy sensors.
In a multi-story facility, there may be a relay panel on each floor controlling all the lights on the floor. Each room on the floor has a local switch and there is also a master switch for the whole floor. The master switch for the floor may be programmed to turn lights on at 7AM and off at 6PM; between 6PM and 7 AM, the system may repeatedly perform an Off sweep to turn lights out where the programming has been overridden.