Fire Alarm Types

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fuze-box

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There are two main types of fire alarms, Conventional and Addressable.

Both types use a 24volt supply usually from two 12volt batteries in series, although there are some makes that use one 12volt battery and generates the 24volts inside the panel.

Conventional types use two wires for the zone about 22 volts, and two wires for the sounders. The pairs of cables come out of the panel to each detector in parallel then terminates at the last detector with an End of Line Device or "EOL".

The EOL is used so the panel knows if the EOL is there then the cable must be intact and all is well, the panel will go into Fire when a resistance of 330 to 560 ohms is present on the zone. An open circuit or short circuit on the zone will cause a Fault condition only.

The sounders are wired the same way, on the sounder outputs in the panel via the internal output fuse to each sounder in parallel and the last one has the EOL fitted.

Some panels on the market use a "two wire system" this has the detectors and sounders on the same two wires, such as Rafiki or MXc by ADT.So when the panel is in fire the pair of wires will have the supply reversed to enable the sounders to operate.

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Addressable types work by having a pair of wires coming from the panel to each detector labled L+ and L- then comes back into the panel known as a "Loop", these usually have about 17 to 22 volts and communicates with each device by software, when a device is in fire it signals to the panel, which responds by putting the sounders on.

When a device is missing or faulty the panel cant communicate so it goes into fault on that device.

Loop Isolators are fitted usually between every 10 to 20 devices.

These are fitted so that if a short circuit was put across the loop, the panel would turn off the nearest two isolators either side of the fault, thus keeping the fire alarm working, unlike the "conventional type" which would put the whole zone out of order.

Sounders can be wired on the loop, or in the same way as the conventional type on the sounder outputs, if they are wired on the loop they will have to be addressable.

Each device on the loop has a unique address given to it by the panel or it is set by the user by "dip switches" or "knock outs" on the back of the device or the base of the device, or programmed by software, depending on the manufacturer of the panel.

The panel is programmed by doing a "Loop Learn Facility" which tells it what devices and how many are on the loop. There can be upto 8 loops on the big types and 2 on smaller panels, and upto 255 devices per loop.

The devices can be given their own "Text" so that if a fire or fault occurs insted of just saying Zone 3 in fire , it gives you its location like "bedroom 12, first floor" etc, thus making it easier to locate the source.

All panels have a set of volt free contacts known as "Aux" to operate fire doors, digital communicators, plant shut down etc.

:D

 

Admin1

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Thanks Fuze-Box.

I thought you got lost. Lol.

:D

 

fuze-box

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240Volt systems dont comply to BS5839, they must be battery back up types.

As for the three wire types its a simple series/parallel circuit. :D

 
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