S95 Components and Power 3 — Questions and Answers
Question 1: 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 2: 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 3: 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 4: 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 5: 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 6: 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 7: 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.
S95 Components and Power 3
A Class B Initiating Device Circuit (IDC) differs from a Class A circuit primarily because: