I85PREP
⌘ K
Georgia Low Voltage Practice study materials
Georgia Low Voltage Practice study resources

Georgia Low Voltage Practice: Fire Alarm and Life Safety Systems

Georgia Low Voltage Practice · Work through your exam, one topic at a time.

All guide sections

Fire Alarm and Life Safety Systems

What this domain tests

Fire Alarm and Life Safety Systems tests whether you can apply NFPA 72 and NEC Article 760 to initiating devices, notification appliances, circuit supervision, and battery sizing. Expect Class A and Class B wiring, end-of-line devices, NAC voltage drop, and standby calculations.

Core rules

  • Initiating device circuits and notification appliance circuits must be supervised. A Class B circuit typically uses an end-of-line device; a Class A circuit returns to the panel and tolerates a single open.
  • Article 760 governs fire alarm cable and wiring methods. Fire alarm cable must be listed for the application and protected from physical damage.
  • Notification appliance circuits need voltage-drop calculations. Strobes and horns have inrush and operating currents; long runs can leave the last device below its listed minimum voltage.
  • Battery capacity is calculated for standby plus alarm time. Commercial systems commonly use 24 hours of standby followed by 5 minutes of alarm, unless the adopted code or designer requires more.
  • Apply aging and usable-capacity factors. A battery that exactly equals the calculated load is undersized.
  • Survivability requirements apply where the system must continue to operate during a fire; check the pathway and cable rating.

Worked example

A panel has 250 mA standby and 1.2 A alarm at 24 V. Standby energy is 0.250 A × 24 h = 6.0 Ah. Alarm energy is 1.2 A × (5/60 h) = 0.10 Ah. Total is 6.1 Ah. Apply 20 percent aging and an 80 percent usable-capacity factor: 6.1 × 1.2 ÷ 0.8 = 9.15 Ah. Select a 10 Ah battery or larger, and confirm the charger can recharge it within the code time. The reasoning is to use both time periods and both derating factors.

Traps

  • Calculating standby only and omitting alarm time.
  • Forgetting that strobe current can exceed nominal during inrush.
  • Using a non-listed cable for a fire alarm circuit.
  • Assuming a Class B circuit supervises the end-of-line device without the correct EOL value.
  • Ignoring battery aging and charger capacity.