Components and Power Flashcards

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

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.

Which battery chemistry is most commonly used as the secondary power source in fire alarm control panels?

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.

How must a fire alarm system respond when primary AC power is lost?

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.

What AC input voltage variation must a listed fire alarm system power supply withstand without operational impairment?

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.

When a fire alarm control panel displays a 'power trouble' indication, what is the FIRST supervisory action?

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.

What device within the fire alarm control panel monitors the primary power supply for loss or degradation?

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.

How frequently must fire alarm system batteries undergo a full discharge (load) test per NFPA 72?

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.

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

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.

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

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.

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

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.

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

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.

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

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.

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

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.

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

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.

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

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.

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

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.

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

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.

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

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.

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

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.

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

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.