Wiring & Installation Practice Questions

Explanation: Class A wiring (also called Style D) uses a loop configuration with separate supply and return conductors, so a single open-circuit fault will not prevent devices from operating — the panel can still communicate with all devices via the alternate path. Class B (Style B) uses a single path with an end-of-line resistor; a single open fault will disable all devices beyond the break.

Explanation: The end-of-line resistor is installed at the last device on a Class B circuit. The FACP continuously monitors the small amount of current flowing through the resistor. If the circuit is broken (open fault) or short-circuited, the current changes, and the panel generates a trouble signal. Without the EOL resistor, the panel cannot distinguish between a normal condition and an open circuit.

Explanation: A Signaling Line Circuit (SLC) is a two-wire circuit used in addressable systems that allows the FACP to poll and communicate individually with each device — detectors, modules, and pull stations — using unique addresses. This enables precise identification of the location of an alarm, trouble, or supervisory condition.

Explanation: The conductor size (gauge) determines the maximum allowable voltage drop on the circuit. The total current draw of all notification appliances on the NAC must not exceed the panel's rated NAC output. Excessive voltage drop caused by undersized wire or too many devices can prevent appliances from operating at rated levels. NFPA 72 requires that the voltage at the last appliance meet the appliance's listed operating range.

Explanation: NFPA 72 and NEC Article 760 require that conductors used for fire alarm circuits meet minimum size requirements. For NAC wiring, 18 AWG is the minimum commonly required for powered notification circuits, though some panels and local codes may require larger gauges for longer runs to limit voltage drop.

Explanation: NEC Article 760 requires that fire alarm wiring be installed in a manner that protects it from damage by other building systems. Keeping fire alarm circuits separate from power and lighting circuits prevents faults in those systems — such as shorts or overloads — from disabling fire alarm circuits during a fire emergency.

Explanation: Isolator modules are placed at intervals on Class A SLC loops. If a short-circuit fault occurs on a segment of the loop, the isolator module automatically disconnects that segment, limiting the fault to only the devices between two isolators. The rest of the loop continues to operate normally through the alternate path.

Explanation: NFPA 72 Section 10.6.6 requires that the primary power supply for a fire alarm system be a dedicated branch circuit from the commercial AC power service. This circuit must be labeled 'FIRE ALARM' and must not be used for any other purpose. Secondary (backup) power is provided by a battery system.

Explanation: NFPA 72 requires that secondary power calculations account for: (1) a minimum of 24 hours of normal supervisory (standby) operation drawing quiescent current, followed by (2) a minimum of 5 minutes of full alarm operation drawing maximum current. Voice evacuation systems require 15 minutes of alarm operation. The battery must supply both without primary AC power.

Explanation: NEC Article 760 requires that cables installed in air-handling spaces (plenums) be listed as FPLP (Fire Power Limited Plenum) cable, which has low smoke and flame-spread characteristics. FPLR is rated for vertical riser shafts, and FPL is for general-purpose use in non-plenum, non-riser locations.