Where should the EOL resistor be placed when installing NC door contacts?

The correct placement of the End-of-Line (EOL) resistor is crucial for the proper functioning of normally closed (NC) door contacts. When installing NC door contacts, the EOL resistor should be placed in series at the device.

By placing the EOL resistor in series with the NC door contact, you are creating a closed loop circuit that ensures the monitoring system can detect if the circuit is interrupted or tampered with. The EOL resistor helps to prevent false alarms by providing a means for the system to recognize the normal state of the circuit. If the door is opened (causing the contacts to open), the circuit breaks, and the monitoring device detects the change in resistance, triggering an alarm.

In contrast, placing it in parallel or at the control panel does not provide the same monitoring capability because the circuit would not properly detect the state of the door contact. Positional placement at the power source would also fail to ensure that the system can accurately gauge the condition of the NC door contacts. Thus, for optimal functionality and security, it is essential to install the EOL resistor in series at the device.