Summary
This article explains the requirements and common configurations for using end-of-line (EOL) resistors for monitoring circuits, including recommended resistor placement, typical resistor value, how EOL resistors detect cable faults, and relevant wiring considerations for relays and power-supply monitoring.
Requirements and purpose of EOL resistors
- An EOL resistor allows the input to detect open-circuit faults on the cable. If the cable is cut or goes open, the input/zone will see the change in resistance (open-circuit) and report a fault.
- A 10 kΩ resistor value is required as an EOL resistor for most monitored inputs.
Typical configurations and placement
- Install the EOL resistor at the end of the monitored circuit (i.e., at the end of the cable, typically where it is connected to a relay/contact or for zone monitoring at the last device).
- Place an EOL resistor in the monitored input so the input does not register a fault when the monitored input is not being used, or, depending on the module, setting DIL switch 8 to the ON position will disable the monitoring of that input.
common wiring pattern for a monitored input when connected to a relay contact
Conclusion
Use an EOL resistor (10 kΩ when specified) in the monitored input to enable open-circuit detection for cable faults. Check EOL specification for each input.