What is the purpose of an end-of-line resistor in conventional circuits?

• A. It increases the range of the circuit
• B. It detects smoke
• C. It aggregates device conditions
• D. It provides a known impedance at the far end of the circuit so the panel can detect opens and shorts

Answer: (D)

The end-of-line resistor provides a known impedance at the far end of a conventional loop so the control panel can supervise the circuit. In a typical loop, devices are wired back to the panel and the panel monitors the line’s current and resistance. Placing a resistor at the far end creates a specific baseline load. If the loop stays intact, the panel sees the expected resistance and operates normally. If the wiring opens anywhere on the line, the circuit is interrupted and the impedance changes beyond the expected range, letting the panel flag a fault. If a short occurs on the line, the impedance drops and again falls outside the normal range, producing a fault or alarm. This end-of-line reference is what lets the panel reliably detect opens and shorts, ensuring circuit supervision. It isn’t about detecting smoke, increasing range, or aggregating device conditions.