S95 Components and Power 2 — Questions and Answers
Question 1: What is the minimum secondary (standby) power duration required for a fire alarm system connected to a supervising station?
- 4 hours standby plus 5 minutes alarm
- 24 hours standby plus 5 minutes alarm (Correct answer)
- 8 hours standby plus 15 minutes alarm
- 48 hours standby plus 5 minutes alarm
Correct answer: 24 hours standby plus 5 minutes alarm
NFPA 72 requires fire alarm systems monitored by a supervising station to operate for 24 hours on secondary power, then supply at least 5 minutes of full alarm operation.
Question 2: Which battery chemistry is most commonly used as the secondary power source in fire alarm control panels?
- Lithium-ion
- Nickel-cadmium
- Sealed lead-acid (SLA) (Correct answer)
- Carbon-zinc
Correct answer: Sealed lead-acid (SLA)
Sealed lead-acid batteries are the industry standard for fire alarm panel backup due to their reliability, maintenance-free design, and proven service life.
Question 3: How must a fire alarm system respond when primary AC power is lost?
- Transfer to secondary power within 60 seconds
- Transfer to secondary power within 10 seconds
- Sound a trouble signal and initiate a controlled shutdown
- Transfer to secondary power immediately and automatically with no interruption (Correct answer)
Correct answer: Transfer to secondary power immediately and automatically with no interruption
Per NFPA 72, the transfer from primary to secondary power must be automatic and immediate, with no gap in system operation.
Question 4: What AC input voltage variation must a listed fire alarm system power supply withstand without operational impairment?
- ±5%
- ±10%
- ±15% (Correct answer)
- ±20%
Correct answer: ±15%
NFPA 72 requires fire alarm power supplies to operate correctly across a ±15% variation in nominal AC voltage to accommodate normal utility fluctuations.
Question 5: When a fire alarm control panel displays a 'power trouble' indication, what is the FIRST supervisory action?
- Reset the panel immediately
- Verify that primary AC power is present at the panel (Correct answer)
- Replace all batteries
- Silence the trouble buzzer and schedule service for next week
Correct answer: Verify that primary AC power is present at the panel
Confirming whether AC power is present at the panel is the first step, as a missing primary feed is the most common and simplest cause of a power trouble signal.
Question 6: What device within the fire alarm control panel monitors the primary power supply for loss or degradation?
- A current-limiting resistor
- A power supervision relay or dedicated supervisory circuit (Correct answer)
- A fuse block
- A voltage regulator
Correct answer: A power supervision relay or dedicated supervisory circuit
The power supervision relay (or equivalent circuit) continuously monitors AC primary power and initiates a trouble signal upon detecting its absence or degradation.
Question 7: How frequently must fire alarm system batteries undergo a full discharge (load) test per NFPA 72?
- Monthly
- Quarterly
- Annually (Correct answer)
- Every five years
Correct answer: Annually
NFPA 72 Chapter 14 requires an annual battery discharge test to verify that batteries can sustain the required load for the full standby and alarm durations.
S95 Components and Power 2
What is the minimum secondary (standby) power duration required for a fire alarm system connected to a supervising station?