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Fire Alarms

Al Letellier
Al Letellier Member Posts: 781
I believe the Mechanical code requires that any AHU over a certain cfm requires these smoke alarm shut down units, ans as the HVAC installer, it's your responsibility. We used to sub out this work, or had the electrical guy do it. We always killed the power circuit as some equipment ran of EMS systems and would run even with no call (air exchange, ventilation, etc.) You could install another relay in the power leg with a 24v coil and use their relay to trip it.

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  • Andy Morgan_2
    Andy Morgan_2 Member Posts: 147

    On commercial and some larger residential jobs, the fire alarm guys want the Air Handlers to shut down so as not to draw air thru the building in case of fire. To do this, they leave me a normally closed relay, low voltage, that breaks when the alarm goes off. They tell me its my job to figure out how to do it, which I don't understand, because I am not the one who needs to shut it down! And it needs to shut down immediatly. I figure I just break the common on the Tstat, everything shuts down. My question is, aren't there some units that have a time delay to shut of after the stat is satisfied? Would'nt a better way be to use a line voltage relay to break power to the unit?

    Andy Morgan

    R. Morgan Mechanical, LLC
  • Mark Hunt
    Mark Hunt Member Posts: 4,909
    They all have a delay

    and you are correct, it would be faster to kill line voltage.

    Mark H

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