OK, here is everything I wish someone would’ve told me when I first became interested in fire alarm systems. I’ll probably forget something.
The fire alarm control panel (FACP) is obviously the centerpiece of any system. They run on 120 volts AC (house current). You will find two main different types: conventional and addressable. This has to do with the panel’s initiating devices (aka pull stations, smoke detectors, heat detectors, duct detectors, sprinkler waterflow monitors, and anything else that is an input). There are a few older less common types, but we won’t get into that right now.
A conventional fire alarm system is set up similarly to the lightswitches and fixtures in your house, except imagine that any of those lightswitches will turn on every single light in the house. This is basically how conventional systems are wired. All of the initiating devices act like simple lightswitches in a row and are wired to zones (sometimes called IDC’s) on the panel. Each zone can support a large number of initiating devices all wired together. Usually, zones will be divided up by the building’s floors or type of initiating device. In the event of a fire or false alarm, the panel does not know exactly which initiating device was set off, but it knows the zone which gives you a general idea of the device’s location. This is why conventional systems are usually only used in smaller buildings these days. In order to make sure that all devices on the zone are connected, an EOLR (end of line resistor) is used on the very last device. The panel looks for the EOLR’s specific electrical resistance in the zone and shows a trouble if it’s not there, meaning that a device got disconnected or the line was severed.
An addressable fire alarm system is much more intelligent. Addressable FACP’s usually have LCD displays and keypads for this reason. Rather than the initiating devices being simple switches, they each have a microchip that communicates data to the panel. Instead of being wired to several zones, addressable initiating devices are wired to one big SLC (signaling line circuit) on the panel. Systems with more than 200 or so initiating devices may have a few SLC’s. In very large systems, multiple addressable panels may be networked together. Every initiating device has an address, similar to IP addresses for computers on a network. The address is usually set either with rotary or DIP switches and often look something like “M1-L2-096” (panel #1, SLC #2, device #96). Every device’s address must be programmed into the panel (some panels do this automatically), and the panel will look for these devices to make sure they’re responding. When one goes into alarm, the panel can tell you exactly which device was activated and where it is located. Addressable devices are NOT compatible with conventional systems and can’t be used without a panel. Only the addressable devices that use the same protocol as the panel will work on that panel.
Some more basic info on initiating devices:
Pull Stations - They generally are either single-action or dual-action. An Edwards 270-SPO is an example of a single-action pull, meaning that it only requires one downward motion to set it off. A Fire-Lite BG-12 is a dual-action pull because it requires you to push in, THEN pull down. Pull stations usually reset with either a key, allen wrench, or screwdriver. For hobbyist purposes, conventional pull stations only use two wires just like a normal lightswitch (+ and - does not matter) and do not require power to work. Addressable pull stations always use two wires, but + and - matters at all times. Some addressable pull stations have an LED that blinks each time it communicates with the panel.
Smoke Detectors - Smoke detectors use either ionization or photoelectric technology. Ionization detectors are rarely used in commercial applications these days, though ionization is always used in cheap 9V smoke detectors. Photoelectric detectors are much more reliable and have become the standard for commercial detection. If you want more info on how these two technologies work, search it on HowStuffWorks. Almost all modern smoke detectors run on 24 volts DC. Conventional smoke detectors are either two-wire or four-wire - a two-wire device draws power from the panel’s zone (+ and - matter), while a four-wire device requires the power input and alarm output separately (+ and - on the connection to the zone do not matter). Two-wire is used most often. Addressable smoke detectors are always two-wire (+ and - matter) and act as remote sensors rather than self-sufficient detectors. This means that addressable smoke detectors do not decide if enough smoke is present to cause an alarm, but instead give the information to the panel to make the decision.
Other initiating devices include heat detectors (very simple mechanical devices that detect temperature rather than smoke), duct detectors (a smoke detector inside a plastic housing that attaches to an air duct and samples the air), waterflow switches (detects if a sprinkler has activated), and beam/flame detectors (optical sensors often used in rooms with very high ceilings that activate upon blockage of the beam).
Now, let’s talk notification appliances. These include horns, strobes, bells, chimes, and speakers. In the lightswitch and fixture metaphor, these would be the light fixtures. They are the output devices that sound when the panel goes into alarm and are used for the purpose of evacuating building occupants. Unlike initiating devices, notification appliances are almost always conventional. Almost all modern notification appliances run on 24 volts DC. Instead of zones, notification appliances are connected to a panel’s NAC’s (notification appliance circuits). Sometimes, the panel’s NAC’s won’t supply enough power for all of the notification appliances in the building, in which case a power booster is used (usually Altronix). Like zones, NAC’s require an EOLR.
Like smoke detectors, horn/strobes are two-wire or four-wire (+ and - always matter). A two-wire horn/strobe supplies power to the horn and the strobe together at all times unless the panel uses synchronization to intelligently set them apart. A four-wire device requires separate power for the horn and the strobe. The reason you’d want separate control over the horn and the strobe is for audible silence - when the horns are silenced, but the strobes continue to flash until the panel is reset. A NAC set to silenceable will shut the horns off when the “silence” button is pushed, and a NAC set to non-silenceable will keep the strobes going until the panel is reset.
A coding is the pattern that a notification appliance sounds in. The most common is temporal (aka code-3), which is three blasts separated by 0.5 seconds of silence, followed by 1 second of silence. The coding can either be set at the panel or on the appliances themselves.
Unlike any other notification appliances, speakers do not use standard power and do not generate their own tones. Instead, a voice evacuation panel generates and amplifies a sound for the speakers to play. These speakers aren’t any different in technology from the speakers in a home theater system. In fact, us hobbyists often test them that way.
Common panel functions:
Ack (acknowledge) - silences the panel’s built-in sounder and lets the panel know that the issue is known about.
Silence - silences the notification appliances
Reset - returns the panel to normal condition if all devices have been reset. The panel will go back into alarm if devices have not been reset.
Drill or Manual Evac - sounds the notification appliances without calling the monitoring station or fire department
Disable - bypasses certain devices
Lamp test - flashes all panel LED’s to make sure they are working (most panels do this when the reset button is pushed)
Common panel LED’s:
Fire Alarm - indicates a fire alarm condition
Prealarm - indicates that a smoke detector is detecting smoke, but not enough to go into alarm, OR that a first-stage device has been activated in the case of a two-stage system
Trouble - indicates that there is a trouble somewhere on the system
Supervisory - an alarm/trouble condition of lower priority such as a tamper switch, temperature monitor, or sprinkler pressure monitor
Silenced - indicates that the NAC’s have been silenced
AC Power - indicates that the system is receiving primary power, flashes when primary power has been cut and the panel has switched to batteries
Ground Fault - indicates that there is a dead short to ground somewhere on the system (has nothing to do with the panel’s AC power ground)
Monitor - indicates that the panel is in the process of doing something (used on EST systems)
If you’d like to learn more, here are some links worth checking out:
The Fire Panel - Device-specific information
http://www.youtube.com/watch?v=eSUUNoW0h_Q - Andrew’s series of videos on the basics of devices
Basic Rules for Panel Care - Basic rules for panel care (a must-read for anyone considering a panel)
Fire alarm control panel - Wikipedia - More about FACP’s
Fire Alarm Codes vs. Standards | Fire Alarms Online - About fire alarm codes
http://firealarmcollector.com/database/Manuals/NFPA%2072%202007.pdf - National fire alarm code (full 2007 edition)