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Fire Alarm -- Description

A fire alarm system is there to detect a fire and then tell people of the fire
A fire alarm system has to have some means of detecting fire, some means letting people know about the fire, power, and some way of carrying the alarm signal to the device letting people know. The Fire Alarm Control Panel is used in most systems to control signals. However, as a concept, it is not necessary to have control panel in all fire alarm systems.
Douglas Krantz -- Fire Alarm Engineering Technician, Electronic Designer, Electronic Technician, Writer

Is the Fire Alarm Control Panel Necessary?

By Douglas Krantz

Having detected a fire, a fire alarm system sounds the alarm. Other than the building wires that carry the signal from the fire detector to the fire horn, everything else in a fire alarm system is just support.

Most Visible

When a customer talks about the trouble that's showing on the fire alarm system, often the customer only means trouble showing on the box-on-the-wall. Sometimes the customer will notice the red horns and strobes high on the wall or the pull stations at the exits, but for the most part, the hidden parts of the fire alarm system are beyond understanding.

It's the Fire Alarm Control Panel or Annunciator that's visible, and to the customer, the heart of the fire alarm system.

The service technician, on the other hand, has to think of the fire alarm system as more than the box-on-the-wall. For the service technician, the main part of the fire alarm system is the detection devices, the wiring throughout the building, and the horns/speakers/chimes/strobes (Notification Appliances).


The fire alarm control panel isn't the fire alarm system: the fire alarm panel doesn't detect fires; the fire alarm panel doesn't carry signals from the detectors or to the horns and strobes; the fire alarm panel doesn't let anyone know about fires. The fire alarm panel only receives signals and provides power to the horns, strobes, and other devices.

When one gets down to it, the early fire alarm control panels didn't really control anything. They only detected trouble with the wiring and they provided power to the devices.

Stand Alone Fire Alarm System

Yes, fire alarm control panels are important control systems, but to understand how important a control panel really is, examine a residential stand-alone smoke alarm.

The smoke alarm has a detection device (smoke detector), the smoke alarm has a sounder to let people know (piezo sounder), and to connect it all together, the smoke alarm has very short internal wires. Without the use of a fire alarm control panel, the stand-alone smoke alarm detects fire, and it lets people know about the fire.

Going one step further with the residential smoke alarms, when there's more than one smoke alarm in the residence, all of the smoke alarms are interconnected with wires; if one goes into alarm, they all sound off. There's no fire alarm control panel, but for all practical purposes, the residence has a full fire alarm system.

Outside Horn/Strobe

Another example is the outside horn/strobe that lets the fire department know water is flowing to suppress fires. It also lets the fire department know where to connect hoses for greater ease in fighting the fire.

The firefighter's outside horn/strobe is powered by utility power. Like a light switch, the flow switch turns on this power, uses wiring to carry this power, and activates the outside horn/strobe.

The firefighter's outside horn/strobe doesn't have a control panel. It doesn't even have anything to detect if the power is turned off or a wire is broken. It's really, though, a complete fire alarm system. (Some people might not consider this as a fire alarm system. However, when heat from a fire is detected by a sprinkler head, water starts to flow, and the outside horn is turned on to announce a fire.)

All this is to say, the fire alarm control panel isn't the fire alarm system.

Take-Away Game

Just to see how important parts of a system really are, sometimes I play an intellectual take-away game; mentally I take away parts of a system, one at a time. Because this is a mental exercise, one can play with ideas and doesn't have to depend on real facts or circumstances.

Take Away the Fire Alarm Control Panel

Starting with the fire alarm control panel, take that away and see what happens.

OK, the Fire Alarm Control Panel does supply power. On the other hand, so does a plug-in power supply.

There's at least one fire alarm manufacturer of addressable fire alarm systems that has a worst case scenario default. In case their fire alarm control panel's processor fails completely, so no data is received or sent on the Signaling Line Circuit (SLC), when the detectors detect smoke or a manual station is pulled, the horns and strobes still sound off. (I've seen this default working.)

In other words, for that manufacturer's Signaling Line Circuit, if the SLC only provides power, the system will still detect fire and sound the alarm. Even when the fire alarm control panel completely rolls over and dies, all that's absolutely needed is a plug-in power supply.

True, this really works only in small fire alarm systems, and most manufacturers' fire alarm systems don't have that as a worst case scenario default (they should get on the bandwagon). However, this mental exercise does show that the control panel isn't always absolutely needed.

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Take Away Anything Else

On the other hand, take away the detector and the rest of the system is useless.

The same with the devices used to let people know about the fire (fire horns, etc.). Take them away and the system is silent.

Or remove the wiring connecting all the devices together, and in case of fire, nothing happens.

Bottom Line

While the customer may think of the box-on-the-wall as the fire alarm system, the technician has to think of the rest of the building's wiring and devices as most of the fire alarm system.

Yes, the fire alarm control panel is part of the fire alarm system, but the fire alarm system isn't just the Box-on-the-Wall. The detectors are what detect the fire, the wire in-between carries this information to the fire horns, and the fire horns sound the alarm.


Douglas Krantz

Describing How It Works

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Electrical Flow

On this website, most references to electrical flow are to the movement of electrons.

Here, electron movement is generally used because it is the electrons that are actually moving. To explain the effects of magnetic forces, the movement of electrons is best.

Conventional current flow, positive charges that appear to be moving in the circuit, will be specified when it is used. The positive electrical forces are not actually moving -- as the electrons are coming and going on an atom, the electrical forces are just loosing or gaining strength. The forces appear to be moving from one atom to the next, but the percieved movement is actually just a result of electron movement. This perceived movement is traveling at a consistent speed, usually around two-thirds the speed of light. To explain the effects of electrostatic forces, the movement of positive charges (conventional current) is best.

See the explanation on which way electricity flows at