Back in 2012 I learned why you never skip the EOL resistor on glass break sensors

Too many new installers I see just loop through the sensor wires without terminating the resistor at the last device. I picked up this habit from a old Sparky at a job on Maple Street in Portland back in 2012. It takes an extra 30 seconds but cuts false alarms by like 80 percent on those old DSC panels. Has anyone else noticed a spike in nuisance calls from systems where the resistor is sitting at the panel instead of at the sensor?

2 comments

2 Comments

johnson.lee1d ago

Jump right into checking the resistor termination on every zone before powering up the panel. I had a customer with a school district that had six glass break false alarms in one week, and it all traced back to the resistor being wired back at the panel (you know, the lazy way). Fixing that one little thing dropped their nuisance calls to zero for the next two years straight.

wrenwilson22h ago

Hang on though, @johnson.lee, that school district actually might have gotten away with the lazy termination if the resistors were at least the right value for the zone. I ran into a similar false alarm issue once where a guy used a 2.2k resistor on a zone that was supposed to be 1k, and it caused the panel to see the line as open when it was actually just borderline. The resistors at the panel can work sometimes, but only if you match the exact spec and the wire run is clean. That six false alarm week sounds like the panel was just barely seeing the glass break as valid because the impedance was off.