Where should End of Line resistors be installed on the loop?

• A. At the control panel
• B. At the power supply
• C. At the last device on the loop
• D. Near the main breaker

Answer: (C)

End of Line resistors are used to establish a known impedance at the far end of a supervised alarm loop so the control panel can monitor the entire wire run for opens or shorts. By placing the resistor at the last device on the loop, the panel sees the true resistance of the whole circuit; any fault along the run changes that impedance and triggers an alarm or fault condition. If the resistor were placed at the panel, power supply, or near the main breaker, faults somewhere along the wiring wouldn’t be reliably detected, or could cause false indications. So, the resistor should be installed at the far end of the loop—the last device on the loop.