S95 Components and Power — 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.

Question 8: A Class B Initiating Device Circuit (IDC) differs from a Class A circuit primarily because:

Class B provides two independent signal paths through a looped return
A single open-circuit fault on a Class B circuit renders all devices beyond the break inoperable (Correct answer)
Class B requires no end-of-line resistor at the far end of the circuit
Class B exclusively uses fiber-optic cable for signal transmission

Correct answer: A single open-circuit fault on a Class B circuit renders all devices beyond the break inoperable

Class B uses a single-path topology; one open fault breaks continuity and disables all devices beyond the break, unlike Class A's redundant looped return path.

Question 9: What is the primary purpose of an End-of-Line (EOL) resistor installed at the far end of a supervised circuit?

To limit fault current during an overcurrent condition
To allow the panel to continuously detect open or short faults by monitoring a baseline current (Correct answer)
To reduce voltage drop across long wiring runs
To filter electrical noise generated by field devices

Correct answer: To allow the panel to continuously detect open or short faults by monitoring a baseline current

The EOL resistor establishes a known baseline current that the panel monitors; any deviation from this value indicates an open, short, or ground fault on the circuit.

Question 10: What causes a 'ground fault' trouble signal on a fire alarm Notification Appliance Circuit (NAC)?

An open break in the positive conductor
An unintended electrical connection between a circuit conductor and the building's grounding system (Correct answer)
A failed notification appliance drawing excessive current
Battery voltage dropping below the alarm threshold

Correct answer: An unintended electrical connection between a circuit conductor and the building's grounding system

A ground fault occurs when a NAC conductor makes unintended contact with a grounded object such as conduit or structural steel, creating an abnormal current path the panel detects.

Question 11: In a Class A Signaling Line Circuit (SLC) configuration, what occurs when a single open-circuit fault develops?

All devices on the circuit immediately stop communicating with the panel
The circuit splits into two segments, both of which remain operational via the loop's return path (Correct answer)
The panel automatically transfers to secondary power to compensate
The fault is silently logged and requires manual review at the next inspection

Correct answer: The circuit splits into two segments, both of which remain operational via the loop's return path

Class A SLC uses a looped return path, so an open fault divides the loop into two segments—each still connected to the panel from opposite directions—maintaining full device communication.

Question 12: Which cable type is required for fire alarm circuit wiring that must remain functional during a fire to support emergency operations?

Standard THHN wire in PVC conduit
Circuit Integrity (CI) rated cable or equivalent fire-resistive mechanical protection (Correct answer)
Category 5e plenum-rated data cable
NM nonmetallic-sheathed cable in concealed wall spaces

Correct answer: Circuit Integrity (CI) rated cable or equivalent fire-resistive mechanical protection

Circuit Integrity (CI) rated cable maintains electrical continuity for a defined period when exposed to fire, ensuring critical circuits operate throughout the emergency.

Question 13: What characteristic is mandatory for all conductors used in fire alarm system wiring per NFPA 72?

Minimum 12 AWG copper rated 600 volts
Listed for fire alarm use or otherwise approved for the specific application (Correct answer)
Installed exclusively in rigid metal conduit
Configured as twisted-pair to reduce electromagnetic interference

Correct answer: Listed for fire alarm use or otherwise approved for the specific application

NFPA 72 requires fire alarm conductors to be listed for fire alarm use or approved by the authority having jurisdiction to ensure they meet life-safety performance requirements.

Question 14: When a short-circuit fault occurs on a Class B Notification Appliance Circuit (NAC), which condition is most likely?

Only devices located past the short activate in alarm
All notification appliances on the circuit are silenced and a trouble signal is generated (Correct answer)
The panel automatically reroutes the NAC signal to an alternate circuit
The short self-corrects once the AC power cycles

Correct answer: All notification appliances on the circuit are silenced and a trouble signal is generated

A short on a Class B NAC triggers the panel's overcurrent protection, which disables the circuit, silences all appliances on it, and generates a trouble signal for supervisory personnel.

Question 15: What is the primary function of the Fire Alarm Control Unit (FACU) in a fire alarm system?

Automatically extinguish fires using connected suppression systems
Receive, process, and annunciate alarm, supervisory, and trouble signals from all connected devices (Correct answer)
Transmit fire conditions directly to the local fire department dispatch center
Supply 120V AC power to all connected smoke detectors on the system

Correct answer: Receive, process, and annunciate alarm, supervisory, and trouble signals from all connected devices

The FACU is the system's central processor: it monitors all circuits, interprets signals from devices, initiates appropriate outputs, and provides the operator interface for system status.

Question 16: What protection device is recommended at the fire alarm control panel to guard against voltage transients on incoming AC power lines?

A standard 20-amp circuit breaker sized for the panel load
A surge protection device (SPD) or transient voltage surge suppressor (TVSS) (Correct answer)
An isolation transformer installed upstream of the panel
A GFCI outlet installed directly upstream of the panel feed

Correct answer: A surge protection device (SPD) or transient voltage surge suppressor (TVSS)

Surge protection devices clamp voltage spikes from lightning strikes or utility switching events, protecting the sensitive microprocessor-based electronics inside the FACU from permanent damage.

Question 17: A 'supervisory' signal on a fire alarm control panel indicates which condition?

A confirmed fire requiring immediate building evacuation
An off-normal condition in a protected system component that needs attention but is not a fire alarm (Correct answer)
Complete failure of the secondary standby power source
A device that has been manually placed out of service by a technician

Correct answer: An off-normal condition in a protected system component that needs attention but is not a fire alarm

Supervisory signals indicate impaired but not failed conditions—such as a sprinkler valve partially closed or a pressure drop—requiring correction to maintain full system protection.

Question 18: What is required when an existing fire alarm control panel is replaced with a new model in an occupied building?

Only the new control panel itself requires testing before returning the system to service
The entire connected system must be retested and verified to confirm compatibility and code compliance (Correct answer)
All initiating devices throughout the building must also be replaced at the same time
The authority having jurisdiction need not be notified for a same-brand panel swap

Correct answer: The entire connected system must be retested and verified to confirm compatibility and code compliance

Replacing a panel can affect system-wide operation; NFPA 72 requires retesting all circuits and devices to confirm the replacement panel properly supervises and responds to all connected equipment.

Question 19: Under NFPA 72, how must an audible trouble signal behave after it has been temporarily silenced at the panel?

It remains permanently silenced until a technician performs a formal reset
It must automatically re-sound if any new or additional trouble condition develops (Correct answer)
It automatically re-sounds on a fixed 15-minute interval until acknowledged
It converts to a visual-only indication after being silenced a single time

Correct answer: It must automatically re-sound if any new or additional trouble condition develops

NFPA 72 permits silencing a trouble signal, but the audible indication must automatically re-sound if a new trouble condition arises so that subsequent faults are never masked.

Question 20: A fire alarm control panel's dedicated branch circuit must be labeled at the electrical distribution panel as:

'Emergency Power' to convey its life-safety priority
'Fire Alarm' and reserved exclusively for the fire alarm system load (Correct answer)
'Protected Circuit' per the National Electrical Code
'Critical Load' in accordance with NFPA 70 Article 700

Correct answer: 'Fire Alarm' and reserved exclusively for the fire alarm system load

Both NFPA 72 and the NEC require the fire alarm system's dedicated circuit to be clearly labeled 'Fire Alarm' at the distribution panel and to serve no other electrical loads.

Question 21: Which component continuously monitors fire alarm field wiring for open circuits, ground faults, and short circuits?

The power supply transformer inside the control panel
The panel's supervisory circuitry operating on each monitored circuit (Correct answer)
The end-of-line resistor acting as a self-contained standalone fault detector
The smoke detector's built-in self-diagnostic drift compensation feature

Correct answer: The panel's supervisory circuitry operating on each monitored circuit

The panel's supervisory circuitry actively monitors every supervised circuit's electrical baseline, flagging deviations as specific fault types—open, short, or ground.

S95 Components and Power

What is the minimum secondary (standby) power duration required for a fire alarm system connected to a supervising station?

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