4 Wire Smoke Detector Question

Can you wire a 4 wire detector to act like a 2 wire detector? Or is this not possible…my alarm has the 2 Input terminals and the contact terminals. My panel only supports 2 wire detectors and I’m not in the mood to run an extra pair of wires through my walls.

Not without 2 extra wires I’m afraid. Your panel does support 4-wire smoke detectors however, see in the manual:


Terminal block 2 terminals 3 and 4 provide (+ and - respectively) power. You just have to program the zone as Normally-open contacts. And you do need an end-of-line relay for proper supervision of power.

There’s no way to jumper the two contacts to the main power terminals? Because in that case wouldn’t it short out and activate the zone anyways?

I’m not sure I totally follow, but if it involves shorting IDC to auxiliary power, that is definitely a bad idea that could seriously damage the panel. No way around using four wires for a 4-wire detector that I’m aware of.

But they are normally open…they close when the detector goes into alarm…

I might just try it one one of my broken panels to see if it will work…but I don’t think it should damage the panel…right? I mean, zones are meant to be shorted

Ok… I may have misunderstood what you were trying to describe earlier. Normally 4-wire smoke detectors should be wired like this:

If you were talking about doing anything like this:

…then that is definitely going to fry your panel. But perhaps you were referring to something like this:

That won’t hurt your panel, but it also won’t work properly for a different reason that I explained <URL url="Reversing polarity on a 2-wire smoke detector]
here[/url]. Basically, you cannot short the supply voltage for the smoke detectors and still have them be powered.

Now theoretically you should be able to simulate a 2-wire detector by doing something like this:

Here you have a resistor in series with the output contacts of the 4-wire detector. I’m not sure exactly what the value of the resistor should be. You would have to so some calculations based on the alarm current of a standard 2-wire smoke detector. I has to be a high enough resistance that you do not bring the voltage to zero, but low enough that the panel senses the change in current and goes into alarm.