WHICH OF THE 2 FIRE ALARM SYSTEM WIRINGS SHOULD YOU USE?
Fire alarm system wiring methods and detectors’ connection are very important in the fire alarm design phase.
In fire alarm design stage you should determine which type of fire alarm system wiring you will use depending on your application and accordingly the fire detectors’ wiring schematic.
We have two main types of fire alarm systems:
- The conventional fire alarm system
- The addressable fire alarm system
Conventional fire alarm system wiring:
In conventional fire detection system wiring, the connection method comes when you connect fire alarm detectors (whether smoke detectors or heat detectors) together in parallel connection and this connection to be ended with an end of line resistance “ELOR”.
Typical conventional fire alarm system wiring diagram as described below:
Firstly you should connect the two wires that are output from the fire alarm control panel to each fire detector, and then at the end of that line connect the end line resistance.
But what is the need for the end of line resistance “ELOR”??
The end of line resistor should be connected at the end of the line in conventional fire alarm systems only.
It has two main functions:
Firstly, It keeps the voltage of the line balanced say if there must be 24 VDC on the detectors all the time to make the detectors work properly, so it keeps the line voltage 24 VDC.
(Its value is determined upon the required voltage depending on the system used).
The other purpose of EOLR’s is to allow the fire alarm control panel to differentiate and segregate between two different conditions by looking for a predefined resistance value of the line:
Condition 1 : Open circuit as “fault”.
Condition 2 : Low resistance circuit as “alarm condition”.
We will explain them in details:
In the normal operation in fire detection systems the detectors are connected as an open circuit and the panel measures a resistance of EOLR (ex: 3500 Ω ; condition #1)
If a fire broke out, the fire alarm detector senses the smoke (if it is smoke detector) that was generated from fire and converts its resistance from (∞Ω) open circuit to about 500 Ω (i.e. less than the 3500 Ω of the ELOR; condition#2).
In this case the fire alarm control panel measures another resistance than the line normal resistance (the 3500 Ω); Its a fire case. Then the fire notification devices and the outputs of the fire system are activated.
Addressable fire alarm system wiring:
In the contrary in the addressable fire setection system, you will not use an end of line resistor ELOR but instead it uses a technology that sense and follow up each fire detector individually. The connection method defines addresses and details.
In the addressable fire detection system each detector in the system is identified as an individual point with its own address.
In the addressable fire detection system, the fire alarm system wiring schematic diagram as described below:
Each detector has 4 connections (2 inputs & 2 outputs)
The connection is done in the detector body.
The detector body is given an address (serial addressing).
In the addressable fire alarm system wiring the fire alarm control panel can detect if the fire detector is in fault condition or in fire condition.
The addressable fire alarm system wiring is more appropriate for large scale building applications as you can cover points up to 256 as compared to conventional which can only cover 32 zones. It is considered smarter than the conventional fire detection system. Nevertheless each one has its own advantage and disadvantages and you should prefer choosing one to the other according to your application.
Almost every country has its own national code which lays out the installation standard for fire alarm systems such as the NFPA 72 for US or the international standard from ISO which is 7240-14:2013.
See the difference between addressable and conventional fire alarms.
Do you want to know fire alarm system basics and design techniques to protect your house and assets from fire?
Get you eBook copy today to acquire the essential information for everyone about fire alarm systems basics, design, installation and testing fire alarm system procedures.
Comments are closed.