Why we use the end of line resistor in fire alarm system?

 

Kidde EOL-15 End of Line Resistor 15K Ohm

The function of an end of line (EOL) resistor is to monitor the integrity of the circuit in a fire alarm system. This is achieved by placing the resistor at the end of the wiring loop, completing the electrical circuit. The control panel of the fire alarm system continuously monitors the resistance of the circuit, which should match the resistance value of the EOL resistor. Any changes from readings may indicate a potential issue, prompting the system to signal a trouble condition.

An EOL resistor should always be installed as the last device in the loop and never inside the control panel. Placing resistors anywhere other than the end of the line does not serve a purpose.

Open Circuit Detection

When there is a break in the wiring or a device is disconnected, it creates an open circuit. This means that the electrical current cannot complete its path through the circuit, resulting in an increase in resistance. The EOL resistor, placed at the end of the circuit, helps the control panel detect this increase in resistance. The control panel is programmed to recognize the expected resistance value of the EOL resistor. If resistance increases, the panel signals a trouble condition.

Short Circuit Detection

A short circuit occurs when two wires come into contact, creating an unintended path for the electrical current. This causes a decrease in resistance, as the current can bypass part of the circuit. The EOL resistor helps the control panel detect this change in resistance. By monitoring the expected resistance value, the control panel can identify when a short circuit has occurred and signal a trouble condition.

Ground Fault Detection

Ground faults occur when a wire comes into contact with a grounded surface, creating a partial short circuit. This can cause intermittent faults and reduced sensitivity in the fire alarm system. The EOL resistor helps the control panel detect ground faults by monitoring changes in resistance. When a ground fault is detected, the control panel signals a trouble condition.

Device Supervision

Fire alarm systems rely on various devices, such as smoke detectors, heat detectors, and manual call points, to detect the presence of fire or smoke. The EOL resistor enables continuous supervision of these devices by ensuring that the control panel can monitor the resistance of the entire circuit. If a device malfunctions or is disconnected, the resulting change in resistance is detected by the control panel, which signals a trouble condition. This ensures that any issues with the devices are quickly identified and addressed, maintaining the system's overall reliability.

Implementing EOL Resistors

Selecting the Resistor Value

The value of the EOL resistor must be carefully selected to match the specifications of the fire alarm system. The resistance value is typically provided by the manufacturer of the control panel and must be adhered to for proper system operation. Using an incorrect resistor value can result in false alarms or failure to detect real faults, compromising the reliability of the system.

Proper Placement of the Resistor

The EOL resistor must be placed at the end of the wiring loop, completing the circuit. This placement is crucial for the control panel to accurately monitor the integrity of the circuit. The resistor should be securely connected and protected from physical damage or environmental factors that could affect its resistance value.

Compliance with Standards and Regulations

Fire alarm systems must comply with various safety standards and regulations, such as those set by the NFPA, Underwriters Laboratories (UL), and local building codes. These standards often include specific requirements for the use of EOL resistors. It is important to ensure that the system design and installation adhere to these requirements to achieve compliance and ensure the safety of the building and its occupants.

Testing and Maintenance

Regular testing and maintenance of the fire alarm system, including the EOL resistors, are essential for ensuring continued reliability and effectiveness. This includes periodic inspections to verify the integrity of the wiring and devices, as well as testing the resistance values to ensure they match the expected values. Any faults or discrepancies should be promptly addressed to maintain the system's performance.

End-of-Line resistors are a vital component in fire alarm systems, playing a crucial role in ensuring the integrity and functionality of the system. By providing continuous monitoring of the wiring and devices, EOL resistors help detect and signal faults such as open circuits, short circuits, and ground faults. This enhances the reliability of fire alarm systems, ensures compliance with safety standards, and improves maintenance and troubleshooting processes.

In summary, the use of End-of-Line resistors in fire alarm systems is a crucial practice that enhances safety, reliability, and compliance. By ensuring continuous supervision and prompt detection of faults, EOL resistors help create a safer environment for building occupants and provide greater confidence in the effectiveness of fire alarm systems.

DRAGONSDEAN ENTERPRISE | SERVICES

Location: Iligan City, Lanao del Norte, Philippines

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