What is an “end-of-line” resistor in fire alarm circuits?

An “end-of-line” resistor plays a crucial role in fire alarm circuits by serving as a means to detect the integrity of the circuit. This resistor is placed at the termination point of the circuit loop. Its primary function is to ensure that the circuit is closed and to detect any potential faults, such as short circuits or open circuits. When the circuit is intact, the resistance value of the end-of-line resistor is measured; if the resistance changes due to a fault, the fire alarm control panel can identify that there is an issue in the circuit. This helps in maintaining the reliability of the fire detection systems, ensuring that all components are functioning as they should, which is critical for safety in fire emergencies.