Home Forums System Recommendations, System Design 2-Wire or 4-Wire Smoke Detectors?

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    I apologize if this is a nwebie question, but I want to get the design right before I start ordering/installing anything…

    I am planning to replace the old Moose Z2000 panel in our house with a new DSC PC1864 panel.

    The house currently has ten 120-Volt smoke detectors that are interconnected via a third wire – if one trips, they all sound.

    I'm planning to replace those with 12-Volt hard-wired smoke detectors with internal annunciators that can work with the DSC panel and I'm confused as to the differences between 2-Wire and 4-Wire smoke detectors.

    As I understand the panel documentation, 2-wire smokes will be connected in parallel between AUX+ and PGM2 with a 2.2K EOL resistor.  If triggered, there will only be a general fire alarm report and you won't be able to determine which smoke was tripped.

    4-wire smokes will all be paralleled between AUX+ and PGM2 for power, but have seperate contacts which are wired one or several to a zone.  These smokes must be latching type (I think that means once tripped, they stay tripped until reset) and need a Power Loop Supervisory Relay at the last detector in each zone. Using 4-wire smokes means that the zone that was tripped can be identified later in the logs.

    #1 – Do I understand the above correctly?

    #2 – For an installation with ten detectors and no shortage of hardwired zones, wouldn't it be preferrable to use 4-wire smokes and dsitribute those between multiple zones?

    #3 – What are the other pertinent differences between 2 and 4-wire smoke detectors?

    #4 -  Will these 12 Volt smokes still sound in unison (when one is tripped, they all sound)?




    Try to make this short and sweet!

    #1 Basically…yes
    #2 I would to make future possible troubleshooting easier.
    #3 Covered by #1
    #4 The feature you refer to is called "tandem" wiring.  I am unaware of any 12 volt devices that offer that feature.  Also, there is a limit to how many you may connect in this configuration.

    Good Luck!


    DEL Installations

    Clarifications not covered in the short answer, which are very important:

    1. Yes and no, the 2 wire units are installed in a daisy chain, from detector to detector. No more than 2 wires would be landed between the PGM and AUX

    2. Can be done, but when replacing your existing detectors you will need to provide audible smoke detectors that tandem ring. More difficult with multiple 4 wire fire zones, as well as when resetting the system you will have X amount of zones going into trouble.  I would not recommend doing such just for that reason.

    3. Separate power and circuit vs. integrated on 2 conductors. 4 wire is more "intensive" as far as wire and related hardware to install for proper supervision, reset, etc.

    4. Most smokes now that have integral sounders allow the installation of a reversing relay to provide tandem ring functionality. As far as how it's implemented, it depends on the panel and smokes.

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