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DE Fire Alarm study materials
DE Fire Alarm study resources

DE Fire Alarm: Circuits, Pathways, and Wiring Requirements

DE Fire Alarm · Work through your exam, one topic at a time.

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Circuits, Pathways, and Wiring Requirements

This domain tests survivability and supervision. NFPA 72 Chapter 12 defines pathway classes and survivability levels; NFPA 70 Article 760 governs the wiring method, cable type, and separation from power circuits. Delaware exams often combine a class question with a voltage-drop calculation.

Pathway classes

  • Class A: the circuit leaves the panel and returns. A single open or single ground fault does not prevent operation of devices beyond the fault. T-taps are not permitted.
  • Class B: no return path. A single open fault disables all devices beyond the break; that is acceptable for many occupancies but not where survivability is required.
  • Class X: Class A performance plus fault isolation so a single fault does not disrupt the rest of the pathway - common on networked and addressable systems.
  • Chapter 12 also defines Class N networks and survivability levels; higher levels apply where circuits serve evacuation signaling or emergency communications.

Wiring and supervision

  • Article 760 divides circuits into power-limited (PLFA) and non-power-limited (NPLFA). Cable types: FPL (general), FPLR (riser), FPLP (plenum).
  • Fire alarm cable must be separated from Class 1 power conductors, typically by 2 in. or a barrier, unless the wiring method is otherwise permitted.
  • Pathway faults - open, short, ground - must annunciate as a trouble signal within the time the code allows (commonly 200 seconds).

Worked example

A notification appliance circuit runs 250 ft one way from the panel to 12 horns drawing 0.075 A each at 24 V. Total current is 0.9 A. Using 14 AWG stranded copper at 3.07 ohms per 1,000 ft, the round-trip resistance is 500 ft ÷ 1,000 × 3.07 = 1.535 ohms. Drop = 0.9 A × 1.535 ohms = 1.38 V, so the last device sees 24 − 1.38 = 22.6 V. That stays above 20.4 V (85 percent of 24 V), which is the usual design floor, so the circuit passes. Note the calculation is conservative because current drops off along the circuit; using full current over full length errs on the safe side.

Traps

  • Assuming a Class B circuit survives an open fault.
  • Drawing T-taps on a Class A circuit.
  • Mixing FPLR and FPLP in the wrong space (plenum requires FPLP).
  • Forgetting that voltage drop is measured to the last device, not the first.