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Wiring
Since every site is different, it is only possible to give general guidance,
refer to BS5839 part 1, for more details.
A fire alarm system depends on it's wiring. There are two group classes of
cable:
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Cables NOT required to operate after a fire has been detected e.g.
detectors and manual call points (group 1).
-
Cables required to operate during a fire, e.g. for sounders (group 2).
Group 1
While mineral installed cables are preferable for all fire alarm
applications, the following cables can be used for the two groups:
1. PVC - insulated to BS6004 sheathed or non-sheathed with mechanical
protection.
2. Rubber insulated to BS6007.
3. PVC single type BK, BR and BU to BS6231.
4. PVC insulated SWA to BS6346.
5. Cross-linked polythene or hard ethylene-propylene rubber insulated SWA to
BS5467
6. Polyethylene insulated PVC sheathed coaxial cable to the dimensional
requirements of BS2316: Part 3 but with a minimum of 16 strands / 0.2mm
diameter central conducter.
Group 2
1. MICC to BS6207: Part 1 (with or without sheath)
2. Cables complying with BS6387 categories AWX, SWX, A or S.
Certain cables may also need mechanical protection against impact, abrasion
or rodent attack.
Conducters carryng fire alarm power or signals should be separated from
conducters used for other systems.
Cables should be installed in accordance with the good practices recommended
in the 16th edition of the IEE Wiring Regulations (BS7671).
Connection to mains supply should be via an isolating switch fused spur
unit, reserved solely for the purpose. It's cover must be red in colour and
labelled FIRE ALARM - DO NOT SWITCH OFF.
All cabling and wiring associated with fire alarm cable circuits, must be
mixed with any other circuit.
Conductor size should also take voltage drop into account. In any case
conductors should have a cross-sectional area of not less than 1mm2 or if
stranded of not less than 0.5mm2
Where possible cables should be routed through areas of low fire risk.
Cables installed in damp, corrosive or underground locations should be PVC
sheathed. Where there is a risk of mechanical damage, cables should be
protected accordingly.
cables in cavities or voids should be separated from other cables by 300mm
unless enclosed in conduit, ducting or trunking. |
