Wiring For HVAC Shutdown Using Low Current Fire System Relay With High Current Relay

When a fire alarm occurs it is common to shut down HVAC equipment to reduce the spread of smoke and air to feed a fire. In some cases, positive pressure fans are turned on to create a high pressure area in stairwells which keeps smoke out. In either case, these fans draw more current than a fire system relay is rated to handle. A RIB (Relay in a box) is often used, or some similar relay, to switch ON or OFF a HVAC system. A fire system relay rated for 120 VAC .5 amp is used to control a high current relay. The drawing below illustrates such an install. 

Wiring for Fire Relay to shut down HVAC

RIB brand relays are commonly used for there ease of installation. The RIB attaches to  a box through a 1/2 KO. The LED light provides indication of status for easy verification of the systems operation. 

RIB relay
There are dozens of models to accommodate various needs. 

 

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