Douglas Krantz - Technical Writer - Describing How It Works
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How are the Horns and Strobes Activated?

In either an Addressable Fire Alarm System or a Conventional Fire Alarm System, the horns and strobes are powered on with the control panel when it goes into alarm. The control panel goes into alarm when an input detection device senses an alarm.

How are the Horns and Strobes Activated?


Greetings Douglas,

Kindly elaborate the circuitry of conventional and addressable fire system, and means of actuating the Notification Appliances.

Thank you, R C

All Fire Alarm Systems

A fire alarm system is a Detect Fire and Warm People about the Fire system. It has automatic detection devices like smoke detectors, heat detectors, and waterflow switches; it has manually operated input devices like pull stations and MCPs (Manual Call Points).

The detection devices send their alarms to a Fire Alarm Control Panel or FACP. Automatically deciding what to do when there are alarms, the control the control panel has circuitry to sound the alarm. Providing electrical power to the detection devices and notification appliances, the control box also has a power supply.

NAC Provides Power to Sound the Alarm

When the control panel (FACP) sounds the alarms, it provides power to the horns and strobes (Notification Appliances).

When the FACP isn't sounding the alarm, it is providing backwards voltage on the Notification Appliance Circuit (NAC). When it's backward voltage, the wires in the NAC circuit are being checked; the backwards voltage can't be used by the horns or strobes. When the FACP is sounding the alarm, it is providing forward voltage on the NAC; because the voltage is now forward, the horns and strobes can use the power and sound the alarm to warn people.

Unless it has addressable horns and strobes, that process is common to almost all fire alarm systems.

Fire Alarm Control Panel

No manufacturer will ever tell you or tell me how their Fire Alarm Control Panel works. The most they will ever you or me is that the panel works.

Conventional and Addressable

Most building wide fire alarm systems have conventional devices, and the addressable systems, besides having conventional devices, also have addressable devices. The addressable devices are most often connected to the panel using a SLC circuit (Signaling Line Circuit).

The conventional devices are often connected directly to the panel on IDC circuits (Initiating Device Circuits) and on NAC circuits (Notification Appliance Circuits). Often, using conventional circuitry, the conventional devices are connected to addressable modules, and then the addressable modules are connected to the panel using the SLC.

Douglas Krantz
Based on his electronics training, and his understanding of Life Safety, Douglas Krantz has compiled his knowledge of Conventional Fire Alarm Systems into the book Make It Work - Conventional Fire Alarms. The book covers the basics of the Conventional Fire Alarm System, and shows how Life Safety and internal supervision affects the fire alarm system.

Douglas Krantz -- Fire Alarm Engineering Technician, Electronic Designer, Electronic Technician, Writer

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