Fire Alarm System Fundamentals and Terminology
A fire alarm system is a chain: initiation, signal processing at the control unit, notification, and (usually) off-premises transmission. Candidates must be fluent in the vocabulary that questions turn on. Initiating device covers automatic detectors and manual pull stations. Notification appliance covers horns, strobes, speakers, and combination units. Initiating Device Circuit (IDC) is the circuit to detectors and pull stations; Notification Appliance Circuit (NAC) is the circuit to horns and strobes. Confusing IDC and NAC is the most common trap.
Know system types: conventional (zones, no point identification), addressable (each device has an address), and analog addressable (control unit polls analog values and applies alarm thresholds). Know protected premises, supervising station (central, proprietary, remote, or auxiliary), and public emergency alarm reporting system.
Understand alarm, supervisory, and trouble signals as three distinct conditions. A supervisory condition (valve closed, low water) is not an alarm and not a trouble. A trouble means the system cannot perform its intended function. Questions love to ask which signal a given event produces.
Rule of thumb: if the event means "something may be wrong with the system itself," it is trouble; if it means "a fire condition exists," it is alarm; if it means "a suppression system or its water supply is off-normal," it is supervisory.
Worked example: A sprinkler control valve is closed. This is a supervisory signal, not a trouble and not an alarm. A break in the wiring to a smoke detector is a trouble. Smoke at a detector is an alarm.