Fire Alarm and Life Safety Systems
Domain 5 tests fire alarm and life safety systems under NFPA 72 and NEC Article 760. Questions cover initiating devices, notification appliances, circuit classes, supervision, battery sizing, voltage drop, spacing, and acceptance testing. The exam expects you to distinguish survivability and supervision requirements from ordinary low-voltage wiring.
Circuits and devices
- Initiating device circuits (IDC) connect detectors and pull stations; notification appliance circuits (NAC) power horns, strobes, and speakers; signaling line circuits (SLC) carry addressable data.
- Class A circuits survive a single open and continue to operate; Class B circuits do not. Supervision detects opens, shorts, and ground faults; end-of-line resistors are common on conventional zones.
- Notification must be audible and visible where required, with candela ratings, synchronization, and ADA-compliant levels. Voice systems add intelligibility requirements.
Worked example
A 24 V NAC supplies 1.25 A over a 200 ft one-way run of 14 AWG copper. 14 AWG is about 3.07 Ω per 1,000 ft. Conductor length is 400 ft, so R = 3.07 × 400 / 1,000 = 1.23 Ω. Voltage drop = 1.25 × 1.23 = 1.54 V. The far end sees about 22.46 V. If the appliances are rated 16–33 V, the circuit is acceptable; if the lowest rated appliance needs 20 V, it is still acceptable but with less margin. At 2 A, drop would be 2.46 V and the end voltage 21.54 V, so the same wire may fail a longer or heavier circuit.
Traps that cost marks
- Using non-fire-alarm cable where FPL/FPLR/FPLP is required.
- Omitting end-of-line resistors or misplacing them.
- Sizing batteries without standby time, alarm time, derating, or aging factor.
- Confusing Class A and Class B supervision.
- Ignoring fire marshal plan review and acceptance testing.
Exam-ready summary
Identify the circuit type, verify cable listing and supervision, then calculate voltage drop and battery capacity. Life-safety work is judged by documentation and acceptance, not just operation.