4-Wire smoke detectors with home runs

Question

Our house has 10 wired smoke detectors. They are currently 2-wire sensors - but each is on a separate home run back to the panel...each has an EOL resistor at the detector.

The old panel (a DMP I think) had some kind of auxiliary box to take each of the separate circuits and either combine them as one zone, or have them as individual zone (I don't know, it never worked properly)

We now have a new Ademco vista panel...and obviously this poses a problem with this unusual configuration.

However - although they are 2-wired, the actual wiring is a 4-wire run (with the green/white just snipped at both ends.

What's the best approach to get them all working with the Vista panel? Switch to 4-wire with home runs, or try and convert to a daisy chained 2-wire?

I've never seen them wired this way...so a but stumped.

Answer 1

If your careful how you splice you can use the 4 conductor wire as you're guessing, send 2 wire out on red/black, bring it back to the panel on green/white... Send it out to the next detector on red/black... Etc etc, rinse and repeat for 10 detectors. The end of line resistor would then go across the last green/white. That essentially converts your 4 wire home runs to a 2 wire supervised loop.

The problem you will run into is you have about 40 more splices in the circuit than are anticipated. Each splice adds resistance to the circuit, eventually most splices create higher resistance over time due to oxidation. All the extra resistance could eventually give the vista panel a fire trouble condition (not a false alarm tho).

Hint: solder all those extra splices, or use a 3M silicone filled crimp style butt splice. A soldered splice never oxidizes over time. Resistance at 12volts can add up quickly, sometimes you can kludge the end of line resistor to another value to compensate, but you lose the UL listing doing so.