Interfacing a Duct Detector with an AC Unit?

[ClamperTony]

I have seen in my Jurisdiction where when an AC Unit shuts down it trips a trouble on the Fire Alarm Panel through the Duct Detector.

My question is how?

Is the AC Unit providing 24 volts out for engaging a relay on the Duct Detector?

Is the AC Unit providing a dry contact pair of wires so that they can go in series with the supervisory contact on the Duct Detector?

According to the Duct Detector Makers The DT is useless without a powered AC unit.

Thanks

Tony

 

[iwire]

Many units now arrive with factory installed duct smokes and yes they are powered directly from the AC units.

Now if someone comes along and ties that duct smoke into a fire alarm system correctly they monitor the alarm and supervisory contctas on the duct smoke.

So if the power to the unit is shut down the duct smoke supervisory contact will open and put the FACP in 'Trouble' or 'Supervisory' depending on the FACP or the wiring.

This is a nuisance but not a real issue as with the RTU shut down there is no need for the duct smoke to be operational.

I prefer to bring 24VDC from the panel to power the duct smokes but I don't draw the prints so I do what they show.

 

[markstg]

I have seen in my Jurisdiction where when an AC Unit shuts down it trips a trouble on the Fire Alarm Panel through the Duct Detector.

My question is how?

Is the AC Unit providing 24 volts out for engaging a relay on the Duct Detector?

Is the AC Unit providing a dry contact pair of wires so that they can go in series with the supervisory contact on the Duct Detector?

According to the Duct Detector Makers The DT is useless without a powered AC unit.

Thanks

Tony

So are you saying when the ac unit cycles under normal operation (say from the thermostat calling for heating or cooling) the duct smoke detector is sending a "trouble alarm" to the Fire Alarm Panel.

Or, when the power to the ac unit is disconnected (like via its local disconnect switch) which would remove power to the complete unit as well as its controls, that this is when the duct smoke detector sends a "trouble alarm" to the Fire Alarm Panel.

In the 1st scenario above, that is bad, and don't understand how this would be acceptable. In the 2nd scenario ok and may be acceptable, but not the best. As Iwire said, that duct smoke detector would be best to be powered from the FACP, and remove all doubt about what the FACP trouble alarm is telling you.

 

[nhfire77]

So are you saying when the ac unit cycles under normal operation (say from the thermostat calling for heating or cooling) the duct smoke detector is sending a "trouble alarm" to the Fire Alarm Panel.

No, there is (typically) a 277 to 24 step down xmfr. As long as the RTU has power the duct smoke does. The relay is normally energized and when it loses power it opens the signal to the FA circuit causing a trouble. It must be wired on the load side of the alarm relay to work properly, as it will open for other troubles as well.

Its not the optimal situation, especially if power is lost, then all the RTU's go into trouble. I haven't seen a RTU powered duct smoke, installed new, in a couple of years.

 

[jusme123]

I am surprised that companies like Honeywell, Simplex and others would allow other smoke det. on their system (they are extremely proprietary) .