Douglas Krantz - Technical Writer - Describing How It Works

Is Class A for Addressable and Class B for Conventional?

By Douglas Krantz | Descriptions

Is Class A for Addressable and Class B for Conventional?

Is Class A for Addressable and Class B for Conventional?

Greetings Douglas,

Can Class A wiring be only used with an addressable fire alarm control panel, while Class B wiring can be only be used on a conventional fire alarm control panel?

Thank You, HN

In a fire alarm system, how a circuit is classified shows how the fire alarm system is going to be affected by something going wrong. Usually, the classification system isn't showing the type of signals are being carried, the classification system refers to the signal carrying capability.

It's mincing words, but the type of circuit isn't the real concern, it's the signal pathway that is being classified, not just the wires. When considering classification, the pathway may be:
  • Wired
  • Fiber Optic
  • RF (Radio Frequency or Wireless)

The signals being carried may be:
  • Conventional
  • Addressable
  • Analog Audio
  • Digital Audio

Because circuits don't detect fire or sound the alarm for people, the circuit is really being watched (supervised) by the fire alarm control panel only to make sure that the detection devices and alarm devices are connected.

Class B Signal Carrying Pathway

One of the major concerns is the ability of a device to send signals to the panel and receive signals from the panel. If a wire comes loose from a connection, if a fiber optic cable breaks, if a radio transmitter or radio receiver (for wireless communication) fails, the pathway is broken.

With Class B, if the pathway is broken, all of the devices beyond the break cannot communicate with the panel.

If a Class B pathway is broken, all devices beyond the break will fail.

Class A Signal Carrying Pathway

Class A pathways go a step further than a Class B pathway. Class A pathways have a second, redundant path from the panel.

With Class A, even if the pathway is broken, there is a redundant path that signal can take between the panel and the devices.

With Class A, this second, or redundant pathway gets switched into service if the panel detects a failure of the original Class B pathway.

Trouble Showing Up on the Panel

By the way, if anything goes wrong with any part of the fire alarm system, in the entire building, the panel is supposed to show a trouble. After all, this is a life-safety system, it's should always work. When the panel shows a trouble, the trouble can be fixed.

Class B and Class A

When something goes wrong, the Classification of a pathway shows what happens to the pathway for the Fire Detection and Alarm System.

Remember, conventional signals and addressable signals are both types of signals.

The Class A or Class B designation has to do with the circuit's pathway. In essence, the pathway is classified to show whether or not a fire alarm control panel can use the pathway to send and receive signals, including the alarms from the fire detection devices.

The signals are messages, the pathway is the route that the messages take.

Douglas Krantz
Life Safety
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