Duct detector power

[jtester]

I've read most of the posts concerning air-conditioner duct detectors. There seems to be a division among installers and designers about where the power to a duct detector comes from when a fire alarm system is present. Does the power for the detector come from the HVAC unit power, which usually causes a trouble signal when the HVAC power is turned off for maintenance, or should it come from the fire alarm panel, which requires additional work on the part of the fire alarm guy?

Can anyone direct me to a code section within NFPA72, IFC, etc., that offers specific instruction on how to power these units.

Thanks in advance for your help.

Jim T

 

[jlive11]

Re: Duct detector power

hello
I am a fire alarm tech in Canada.....any HVAC duct smoke detector installed when a fire alarm is present is powered from the fire alarm panel (every one that I have installed or serviced) 24v DC.

jlive

 

[iwire]

Re: Duct detector power

jlive does this include duct smokes that came factory installed inside large HVAC units?

These units will arrive already wired into the HVAC units control power for shut down and power supply. Typically all we do is monitor them at the FACP.

I have left them supplied from the HVAC system and I have re-supplied them from the FACP. I too am curious if there is a correct answer.

 

[ron]

Re: Duct detector power

It is not specifically stated.
You can power the duct detector from either 120V power or from the fire alarm panel. If there is a fire alarm system, then you must monitor that detector for alarm and trouble.

NFPA 90A-2002 6.4.4.2 In addition to the requirements of 6.4.3, where an approved fire alarm system is installed in a building, the smoke detectors required by the provisions of Section 6.4 shall be connected to the fire alarm system in accordance with the requirements of NFPA 72, National Fire Alarm Code.

NFPA 72-2002 6.15.5.2 If connected to the fire alarm system serving the protected premises, all detection devices used to cause the operation of HVAC systems smoke dampers, fire dampers, fan control, smoke doors, and fire doors shall be monitored for integrity in accordance with 4.4.7.

6.15.5.3 ... Smoke detectors mounted in the air ducts of HVAC systems shall initiate either an alarm signal at the protected premises or a supervisory signal at a constantly attended location or supervising station.

 

[jbwhite]

Re: Duct detector power

Originally posted by iwire:
These units will arrive already wired into the HVAC units control power for shut down and power supply.

I do alot of hvac work, and have never see one come pre wired. Most of the larger units i work on come in sections. Proper duct placement of the pick up tubes prohibits any prewireing.

We too have feed power to the smoke from either the hvac unit or facp. and yes they must be tied to the fire alarm initiaing circuit, and fire alarm notification circuit with some designs.

 

[iwire]

Re: Duct detector power

Originally posted by jbwhite:
I do alot of hvac work, and have never see one come pre wired. Most of the larger units i work on come in sections.

I can guarantee that they are out there.

These units are generally the size of a trailer truck and are roof mounted. They arrive ready to run, drop it on the roof connect the feeder, the control, gas line and turn it on.

There is often a factory installed supply and return duct smoke inside the plenum that will provide shutdown.

Check this link for more info.

 

[jbwhite]

Re: Duct detector power

i didnt say that they were not out there.... thanks for the link. i wanna check that out.

and i want to correct my last post before someone else does. when the ahu is required to be wired to the notification circuit. we normally dont do that in the duct detector. we install a seperate module for that.

 

[ron]

Re: Duct detector power

Regarding the pre-installed units ....
In a computer room, there are pre-packaged units called CRAC's or CRAH's, and they will come with pre-installed smoke detectors that act like duct detectors. Although many times they are not required by code in a recirculating unit of this type, but they are added as an optional item.
http://applications.liebert.com/partsmanuals/dhdeluxe/140752-opt-smkdet.htm

 

[jbwhite]

Re: Duct detector power

ron, your link shows a fire stat, which serves a different purpose. Usually this is a fuse link which only works once. it shuts down the unit, but is typically not fire alarm tied. it is however connected to the same saftey circuit as the smoke detectors, in your case there should be some under the floor.

 

[iwire]

Re: Duct detector power

Click Ron's link then roll your mouse over the '12'.

 

[jbwhite]

Re: Duct detector power

thanks iwire

 

[ron]

Re: Duct detector power

Prior to the 2002 NEC, the detector in the CRAC would not have had smoke detectors below the raised floor (unless specifically requested by the owner, not code required).
Currently, since many jurisdictions have adopted the 2002 NEC or later, I only specify for detectors below the raised floor when we will be using the leniencies provided by Article 645. If we don't need the leniencies, then no smokes below the raised floor. They are difficult to maintain in an operating computer room (circuitry and air flow below the floor).