In a Fenwal double-loop fire detection system, how are the detector units wired?

• A. Directly to the alarm without loops
• B. In parallel within each loop only
• C. In parallel between two complete loops of wiring
• D. In series within a single loop

Answer: (C)

Fenwal double-loop fire detection is built for redundancy, using two completely separate wiring loops. The detector units are wired in parallel between these two loops, meaning each detector is connected across both loops rather than just within one loop. This arrangement lets each detector influence the circuit through both loops, so if one loop is damaged or opened, the other loop can still carry the signal and the control unit can activate the alarm. Wiring the detectors in parallel between the two complete loops provides the necessary fault tolerance that a single loop configuration cannot.