Security & Fire Protection Systems/firex smoke detector model ad


we have this system in our church.One head is in the hallway to our social room.Somebody removed it and it is nowhere in site.Our problem is this head is hooked to our attic fan so when the alarm is activated it shuts off the fan.the fan is on a timer and somehow the timer ac is opened up to shut it off.Can you explain this to me and where can we purchase anew smoke detector...John

Hi John,

You are quite correct in your conclusion on how this fan is shut off - by the opening of the AC on the timer circuit. The smoke head does this by the use of a Relay Module (possibly the FireX 501 module which was compatible with these heads):

Picture Of a 501 Relay Module

Wiring Diagram for the 501 Relay Module

If not a module, then there may be a relay base fitted to the head directly, although on the AD range, this was not common and would have been an upgrade at some point.

The relay's normal state will be C-NC (Common, Normally Closed) so the relay is not under energisation all the time whilst the system is in monitoring mode. When the head detects a fire condition and activates, it uses the signal wire (yellow) to activate the relay, placing it into C-NO (Common, Normally Open) and hence, breaking the supply feed to the timer and fan.

The relay module will either be in a Hex-box behind the base plate of the detector, or in a separate box, placed somewhere within the area, with a cable running from the detector to it.

As for purchasing a new smoke detector, unfortunately the AD range of smoke heads are no longer available as it has been discontinued. If you are lucky, you may be able to find a second hand working unit on eBay or similar. Otherwise, Kidde, the manufacturer of the FireX range, have replacement models that can be used, but to be able to advise you to which model you will need, I will need to know the exact model number of the AD range detector you currently have fitted (this can be taken from any other remaining head on the system. The model number will be printed on the label on the back of the detector head and you will need to remove it from the base to access it). Otherwise, a bit of searching on the web will point you in the right direction if you want to follow up on this yourself.

Hope this helps and feel free to come back if you require further assistance.  

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Malcolm Evans


I can answer questions relating to Fire systems and Gaseous Fire Suppression systems, both mechanical (including Integrity Testing) and electrical components (Addressable and Conventional systems) and can cover UK standards and regulations. Also, I am Ansul trained and certified in R-102 Ansul Kitchen Suppression system design, installation and maintenance.


I have 2 years experience with my current employer, a UK Fire Protection Company, in installation, testing and maintenance of various system types, and design of Ansul R-102 Kitchen Suppression systems.

FIA (Fire Industry Association) and BAFE (British Approvals for Fire Equipment) accredited. Ansul certified.

Secondary Education (GCSE's) and Technical College (City & Guilds).

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