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Non Addressable Fire Alarms

A non-addressable system is simply comprised of Fire zones. These are represented by red l.e.d.s on the control panel.

A zone is how a building is split up to speed the location of a fire. For example if a building was not zoned then in the case of a fire, the whole building would have to be searched instead of being directed to the exact zone area by the control panel. This would dramatically slow up the location process and would result in more damage and possibly loss of life.

Each zone is made up of a grouping of AFD and MCP’s and in the event of a fire being detected either automatically by AFD of manually by a person discovering a fire and operating the MCP,will cause the control panel to enter fire condition which will then operate the alarm sounders thus alerting the occupants.

The Zone in fire condition would then have to be checked to establish the exact detector that caused the alarm. If an AFD was the cause a red l.e.d would be illuminated on the detector itself.

The zone wiring is in a redial circuit and terminated with an end of line device or resistor which enables the panel to monitor the wiring for short and open circuit faults.

When a smoke detector enters fire condition it draws much more current than normal which is sensed by the alarm panel and it turn enters fire condition. A MCP is a simple switch between positive and negative which under normal condition is open circuit but when a glass is broke goes closed. A resistor in series with the positive prevents this being a complete short circuit but again causes a surge in power as with the smoke detector.

The panel will typically have two on board alarm sounder circuits which in normal operation send a reversed voltage down each circuit to monitor for faults. The voltage is reversed otherwise the sounders would be on constantly but is changed to normal polarity in a fire condition.

The panel requires a dedicated 240v ac supply and where it is then reduced down through a transformer and then changed to its operating voltage of 24 volts DC via a bridge rectifier.

As the system operates on DC it can now be battery backed up so in the event of a power failure it will continue to provide cover from 24 hours up to 72 depending on it’s Category. The batteries in the fire panel should be replaced at least every 4 years or when testing dictates.

In this system the physical wiring dictates the zoning and the detector decides if it’s a fire condition or not.

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