Open Circuit: MS-9200UDLS Trouble Code | Fire Alarm Resource Center

What This Code Means

This condition indicates that the control panel has detected a break in the wiring or a missing end-of-line resistor on a Notification Appliance Circuit (NAC).

Common Causes

1Broken or disconnected field wiring in the NAC loop
2Missing 4.7 kΩ End-of-Line (EOL) resistor
3Loose terminal connection at TB3 or TB4
4Incorrect EOL resistor value used for circuit supervision

Resolution Steps

Inspect the Notification Appliance Circuit (NAC) wiring for physical breaks or loose connections at the terminal blocks. Verify that a 4.7 kΩ, 1/2 watt End-of-Line resistor (P/N 71252) is correctly installed at the end of the circuit. Use the panel's Read Status function to check the NAC voltage; a reading of -2.3 to -2.5 VDC confirms an open circuit condition.