Circuit integrity, the ability of a system to keep functioning under adverse conditions, is extremely important when installing low-voltage alarm systems. Probably one of the most significant problems that traditional alarm companies have in ensuring integrity involves the manner in which their technicians install end-of-line (EOL) resistors. These EOL devices are supposed to be wired at the end of each initiating device circuit (IDC).
Most fire alarm technicians know the proper place to install an EOL in a fire alarm system is at the end of an IDC. In fact, all installers worth their weight know and follow this rule of thumb. Fire equipment manufacturers always specify it in their installation manuals.
As a trade journalist in the low-voltage market, I have met many installers over the last 22 years. Most of them rightly put their EOL where they belong when it comes to fire alarm systems. However, an overwhelming majority of them refuse to do this when it involves burglar alarm systems.
Some will say burglar alarm devices are simply too small to install EOLs at the device. Others say burglar alarms do not require EOLs because they’re not involved with life safety. That can be argued based on perspective. Burglar alarm protection is life safety to someone who has been victimized in their own home or after hours at the office.
Of course, there is a right and a wrong way to install EOLs, and it is easy to know which one is correct. All you have to do is look at the nomenclature used by equipment manufacturers. They use the words “end of line” for a very good reason. Otherwise they would call them beginning-of-line devices. If that doesn’t convince you, then take a close look at the panel manufacturer’s installation instructions.
Burglar EOLs same as fire
The first reason it is important to install EOLs at the end of IDCs in fire alarm systems is the fire code. Section 4.3.1 of NFPA 72, National Fire Alarm Code, 2002 Edition, states, “Equipment constructed and installed in conformity with this Code shall be listed for the purpose for which it is used. Fire alarm system components shall be installed in accordance with the manufacturer’s installation instructions.”
In other words, if you haven’t done it already, take a few moments to read through the installation manual before you install a fire or burglar alarm system. For example, in a model MS-5024 fire alarm panel made by Fire-Lite Alarms of Northford, Conn., the installation instructions specify an EOL of 4,700 ohms at ½ watt (4.7K, ½W).
The manual further states: “All wiring between the master and the slave communicator is supervised. End-of-line resistors, 4.7K, should be connected.”
Not only that, but in the MS-5024 manual, there is a schematic diagram illustrating how this is supposed to be accomplished. In the manual, the EOL is clearly shown at the end of the IDC.
Very few low-voltage technicians will argue about EOL placement in fire alarm circuits. And yet, many of these same techs argue about EOL placement in burglar alarm panels.
The danger of panel EOLs
Besides “the manufacturer said so,” there’s another reason for placing EOLs at the end of IDCs in burglar alarm systems. The most compelling of all relates to either accidental short circuits across an IDC or those placed by a burglar to defeat the system.
Placing the EOL as close as possible to the switch/device will stop a burglar from shorting the IDC, which can fool the alarm panel into thinking the door is closed when it may not be. Of course, a simple accidental ground fault could do the same thing. This means the alarm panel will fail to initiate an alarm when the door is opened.
In the case of the EOL installed as close to the door switch as possible, a jumper will cause the alarm panel to see a dead short over the IDC, which will cause it to sound the alarm and notify the central monitoring station that a security breach has just taken place.
COLOMBO is a 32-year veteran in the security and life-safety markets. He currently is director with FireNetOnline.com and a nationally recognized trade journalist located in East Canton, Ohio.