Question:
I was asked by the Fire Chief of one of the local towns to install a relay with dry contact closure onto the 120 volt smoke detector system in the town library. There is already a four channel digital communicator in place for their wireless call buttons with three channels available. The fire alarm system is of course local and consists of 120 volt detectors and several pull stations throughout the building. The detectors are BRK model 2839ACWI. They are all interconnected with three conductor romex. The pull stations are part of this system too although I can't seem to figure out how they connected them to the 120volt smokes. I explained to the Fire Chief that there is no battery backup, supervision etc and he understands and will sign off on it so I have no problem doing this. During a recent phone call to BRK, I was told that the red interconnect wire goes to 9VDC during an alarm condition. We placed a DC meter between building neutral and the red wire and hit the test button on a detector. The meter read .85volt. Next, while still monitoring the red wire, my assistant activated a pull station. I expected to find the same voltage but only noted .08VDC. I can't seem to figure out how they could have wired this building or why this is working this way. I don't normally deal with 120volt systems, most of our stuff is 24volt, so this really has me stumped. BRK has been pretty much useles in the way of technical assistance telling me "no you can't use pull stations with those smoke detectors, they will not work" meanwhile I'm telling them "I'm looking at the system right now and its been working just fine for several years now". And as far as a relay they were no help there either except to tell me that they don't have one and that the red line goes to 9volts on alarm, (which it doesn't seem to either). Can anyone please offer any assistance on this seemingly simple problem?

Answer: You are voiding the UL listing on the smokes. Don't do it. Most smoke detector manufacturers have a 120 volt model with a relay outputs. If the FC does not want you to replace the units and wire the output to whatever they instruct in writing (you do have a contract?) I would pass on the job. You probably already know all of this, so sorry if I sound like I am lecturing. I just wanted to get the word out to others reading hear that if you try to wire to a UL listed device for the an application that it is not listed for, you are voiding the UL listing and can have a very big liability issue if something goes wrong; even if you get the request in writing from the customer. Don't do it. It is not worth your livelihood.