Why do some of system sensors heat detectors have 2 shorting circuits if they both short at the same time? What is the difference between a single circuit and a dual circuit?
A dual contact heat detector can activate a fire alarm IDC and activate some other auxiliary function. One example is replacing a heat detector on a very old system that has one supervised IDC for the entire building and a point wired annunciator. Those circuits have to be kept separate. On older hardwired systems dual contact detectors were used for the elevator shaft and equipment room sprinkler solenoid valve activation. Again, those circuits have to be on different contacts.