What is the purpose of End of Line resistors (EOLR) in a control circuit?

• A. To allow the control panel to supervise field wiring for open or short circuit conditions.
• B. To increase the signal strength.
• C. To isolate the panel from the field wiring.
• D. To provide power to the sensors.

Answer: (A)

End of line resistors provide supervision for the field wiring. By placing a known resistance at the end of a supervised loop, the control panel can continuously monitor the integrity of the entire circuit. The panel expects a specific resistance value when the loop is normal. If the wiring opens, the resistance becomes effectively infinite, signaling an open condition. If a short occurs, the resistance drops to a low value, signaling a short condition. This setup lets the panel distinguish between normal operation and wiring faults, allowing prompt alerts and reliable security monitoring. They don’t boost signal, isolate the panel, or supply power to sensors.