Potter Fire Alarm Systems - Manual (Page 15)

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Fire Alarm Training • 8700055 • Rev F • 4/10
etc.) or cover a geographical area for smoke and heat detection. Most conventional zones use a two-wire system with an end of
line resistor for supervision.
Conventional zones support two types of devices: dry contact and powered. The dry contact type devices are devices that use a
normally open switch that closes on activation and create an alarm. These devices include pull stations, heat detectors, four wire
smoke detectors, flow switches and sprinkler supervisory switches. The powered devices on conventional zones use voltage
from the panel for power and subsequently must be listed for compatibility. In addition, there are a maximum number of smoke
detectors that can be installed on any zone. Most panels are listed with numerous smoke detectors and the exact number of
smokes per panel varies with each manufacturer. Powered devices operate on a “Go/No Go” in that they are either normal or they
are in alarm condition.
The Annex of NFPA 72 recommends that the coverage area for a single zone does not exceed 20,000 square feet and does not
extend beyond a floor of a building. In addition, a maximum of five waterflow switches and a maximum of twenty supervisory
switches can be connected to a single zone. The common devices in a system should be grouped together on a zone. A trouble
condition on a zone should indicate some sort of wiring or device problem.
Addressable
Addressable fire alarm systems assign each initiating device a discrete and unique identification (address). In addition to the
address, the panel will usually have the ability to have a tag to further identify the address (i.e. Address 1, Front Lobby, back door,
hallway, etc). Some addressable systems consider each point as a separate zone. Addressable devices are similar to conventional
devices in that they are either in alarm or in a normal condition.
Addressable systems utilize a Signaling Line Circuit (SLC) to communicate with detectors, modules and auxiliary devices to
complete the system. These types of systems have more versatility and features compared to the conventional systems. Modules
and additional circuit boards allow the addressable systems to expand to perform more remote relay functions, dry contact
monitoring, remote power control, releasing service and conventional zone monitoring.
The addressable systems also allow for mapping of inputs to outputs. This allows the end-user to control the panel in such a way
that specific smoke detectors can control certain output functions.
Addressable fire systems have a number of advantages over conventional systems. The wiring for each zone must return to the
panel on conventional systems, whereas the addressable systems use a single pair of wires and connect to all of the initiating
devices and control modules on the addressable system. In addition, when a trouble occurs with the addressable system, the
information from the panel will help the installer determine where the problem has occurred, if a device is missing or if the wrong
type of device is installed. Conversely, the conventional system will show a trouble condition and the zone where the trouble
occurred. Also, when a device reaches the alarm level, the conventional system will give the area of alarm, the addressable system
will tell what device is in alarm and where that device is located.
Analog/Addressable
Analog/Addressable systems are wired and have the same advantages of a straight addressable system, but offer additional
features that assist in the testing and maintenance of a system. Instead of using a detector that is either in alarm or normal, the
Analog/Addressable system uses a sensor for detecting a level of alarm. The panel and the sensors communicate and the panel
will determine, based on preprogrammed levels, if the device is normal, dirty or in alarm. The analog systems also use modules
for dry contact inputs, power outputs and relays, however these have no analog value to communicate back to the panel, just a
normal or off normal. The installer can run reports from the analog system and determine if devices are within sensitivity levels
within the listed parameters as required by the testing requirements of NFPA 72.
Annuciators for fire alarm systems are available in one of three variations; LED, LCD and graphic. The LED annunciators are
generally simplistic devices that indicate what zone is in alarm, AC power, Trouble conditions and possibly some control features
such as Silence and System Reset. The LCD annunciators give a text display indicating the status of the fire alarm system. Most
LCD displays also allow for common control functions and usually some programming. The graphic displays are large boards
that have a footprint of the entire building usually by floor with LED’s indicating different devices mounted within the building.
Annunciators are required by the AHJ to assist the emergency responders in quickly pinpointing the area of alarm and responding
to that area to verify whether a fire exists. Some AHJ’s have a preference to which type of and the exact location of where
annunciators are to be installed.
Monitoring for Integrity
Since fire alarm systems are used as a life safety and property protection systems they must be designed and installed with a
high level of reliability. The reliability of the fire alarm system is built into the panel in the means of operation and the minimum
requirements to achieve a listed and recognized product.
The core concept behind the reliability of a fire alarm system is based on monitoring for the integrity of the circuits. This is
achieved by the fire alarm control unit supervising each zone, circuit or point. This is accomplished by end of line resistors, end of
line relays and two way communications between the panel and devices throughout the building.