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Here's a question I've always wondered about; If the duct detector only kills the 24v signal (opens R) what happens if the unit is running in heat and the blower is already running? The blower will eventually time out but it will continue to fan the flames until then, right?

im still learning bout these duct detectors too they can be easy to diagnose or very troublesome i actually ran into one that was dropping my 24v to my unit i noticed when blower contactor was pulled in after a min of running would start to chatter n i would get 10v but my transformer would still have 24v supply i trying sever things to figure out what it was long story short it was the duct detector i unhooked the common and unit ran fine. usually when i get into an issue w a duct detector i hvae the alarm company come out too becuase they are the ones that hook the detector up.

Originally Posted by jamesjohan

Hi,I also never wired a duct smoke detector but A my friend suggest me for the wiring of the smoke detector,so Determine the smoke detector's input voltage. The fire alarm system's control panel, located near the air handler, lists the smoke detector's input voltage and labels the control system's wire terminals. Usually two sets of wires extend from the management panel's wire terminals. One set leads to the smoke detector's input power supply and the other leads to the smoke detector's alarm circuit. In some cases, the smoke detector receives its input power from the air handler. Check the control panel's wiring diagram to verify the input power's source.so may it prove helpful for you.thanks

if this is a commercial unit. the power will come from the fire panel and also have a battery back up. I have never seen power supplied form any other source. The battery back up should maintain a charge for at least 90 minutes in the event of power loss.

in duct smoke detectors just cut out 24volts when smoke is detected..

you don't need to learn about fire systems, what you need to know is who to call. If your getting involved with fire systems you most likely will need a permit. i wouldn't waste a lot of time on this, the city will tell you what you need, the fires guys will install it, or tell you what is needed to make code. don't get to involved, you don't want to held liable should something happen.

when all is done you will need to do a smoke test.

Most of my projects have f/a system specific smoke detectors (Simplex, etc.) that are addressable and supplied by my alarm contractor. HVAC contractor mounts the detector and sampling tube in the duct and brings in +24v to the NC for the detector to break on alarm. Generally the alarm is set to signal "trouble" at the panel and not "fire" so we don't get a full alarm with trucks and evac. for a smoking belt/motor/etc. I think NFPA exempts systems that don't share any ductwork (inc. fresh air) up to 2,000 CFM. Systems over 15,000 CFM need supply and return. Better info can be found in NFPA 90a and NFPA 72(?) I think.

Sequence of operations usually also dictates that a full shutdown of all equipment in the building will occur if there is a full alarm. This is the alarm guy's job.

Testing is the alarm contractor's job the first go round, and the owner's problem for quarterly inspections and annual testing. Of course the inspections and testing must be done by a certified contractor and well documented, and most jurisdictions want copies of all your logs on file with the fire marshal, especially deficiency reports. Fire alarms are an absolute annuity.


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Is this a new construction job where you will be adding RTU units to the theater? Or are you just adding Smokes to existing duct or equipment? i assume for a theater and the occupancy codes that govern this building that there is a large fire and smoke alarm system being installed by others????

If new construction and with RTU units, they can be ordered with factory installed return, supply, or both. Or these can be field installed after the new RTU's are installed. Many higher end RTU's with on-board computer can be set-up as what to do in case of the smoke detector trips.

In most cases on job sites you will have a controls or alarm company doing wiring? They will usually have a set of drawings and know how they want there alarm panel to tie onto the HVAC Equipment and what they want the equipment to do in case of smoke (shut off, blower on, exhaust venter on, etc). Most of the time, control and alarm companies do all the wiring to and from my smokes. I am just there to commission the system and may be present during the fire marshal's walk through, test, and inspection. I also usually am asked to break the main control wire to the system for them...like running the 24v line from the transformer through the smoke's NC contact back to the unit, so as to kill the system in case of a fire or smoke alarm...that is about as far as I usually go.
If adding smokes to just the duct work, it is pretty much the same thing. Need to set down with the controls or alarm people and see what the plan is. They should be running fire rated (RED) control wiring too and from the equipment anyways.
Also if your installing the smokes or if they are coming pre-installed in the equipment, you will probably want to remove the smoke heads and set them aside until new construction is finished. Code requires that they either be removed or protected during construction. Dry wall dust, paint particles, etc. will destroy the heads.

Originally Posted by valdelocc

we only look at em when there is a problem and we find the detector cover with dust and junk, I've attempted to clean them a few tines and its always a gamble, got called back cause of it so now when I find one tripped for no reason, I replace it.

x2

Originally Posted by Control Man

Here is some basic info http://www.systemsensor.com/pdf/A05-1004.pdf

cool site control thx!

I did some reading and will find out more. the theater will have to have a separate detection system. I will have plans later and will figure out how and if they communicate with each other or just the AHU.

Thanks again guys

well its in a theater so i would think thru an alarm, but as it goes i don't know yet. thanks for the help

Originally Posted by valdelocc

think of it as a relay with normally open/closed contacts, typically the R 24v control wire is re-routed through the normally closed terminals on the SD,when the detector trips it kill the 24v and shuts the unit down, in some cases the G terminal is use to kill the blower. most modern RTU's come equipped with inputs for the SD signal, the open/closed configuration varies.
The maintenance of duct detectors falls into a gray area, fire alarm companies leave it to HVAC contractors and the other way around, we only look at em when there is a problem and we find the detector cover with dust and junk, I've attempted to clean them a few tines and its always a gamble, got called back cause of it so now when I find one tripped for no reason, I replace it.

Just a tip. I have had great luck cleaning them out with dry nitrogen. It seems to get the job done most of the time.
(rcac101) Will they be independent or wired through a fire alarm?

Originally Posted by rcac101

Hey guys, i need to learn about commercial smoke detectors how they are wired and how they work together.
can anyone direct me. I will be at the supply house tomorrow and get more of a direction
I am starting a commercial job in a few weeks and need to know about this.

thanks

Roger

think of it as a relay with normally open/closed contacts, typically the R 24v control wire is re-routed through the normally closed terminals on the SD,when the detector trips it kill the 24v and shuts the unit down, in some cases the G terminal is use to kill the blower. most modern RTU's come equipped with inputs for the SD signal, the open/closed configuration varies.
The maintenance of duct detectors falls into a gray area, fire alarm companies leave it to HVAC contractors and the other way around, we only look at em when there is a problem and we find the detector cover with dust and junk, I've attempted to clean them a few tines and its always a gamble, got called back cause of it so now when I find one tripped for no reason, I replace it.

Here is some basic info http://www.systemsensor.com/pdf/A05-1004.pdf

.
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in duct smoke detector

Hey guys, i need to learn about commercial smoke detectors how they are wired and how they work together.
can anyone direct me. I will be at the supply house tomorrow and get more of a direction
I am starting a commercial job in a few weeks and need to know about this.

thanks

Roger