Fire Testing

1. DESIGN STANDARD IN ACCORDANCE WITH DIFFERENT STANDARDS
BS 7629-1:2008 – Electric cables. Specification for 300/500V fire resistant screened cables having low emission of smoke and corrosive gases when affected by fire. Multicore and multipair cables.
This standard apply to cables with thermosetting insulation of rated voltage 300/500V which conform to the performance requirements for cables required to maintain limited circuit integrity under those fire onditions of BS 6387 specified as B, W and X. Those cables are intended for use in fire alarm and emergency lighting applications.
The cables are suitable for operation at a maximum sustained conductor temperature of 70°C although the insulation is suitable for operation at higher temperatures. Use at a temperature not exceeding 90°C is allowed for terminations within an enclosure providing the cable conductor temperature outside the enclosure does not exceed 70°C.
The standards apply to cables with a rated voltage of 300/500V, and -two, three and four-core circular cables with uninsulated circuit protective conductor
-7,12 or 19 core with an uninsulated drain wire
-1,2,5,10,20 pairs having a collective metallic layer and drain wire.
They contain a metallic layer which provides electrostatic screening.
BS 7846:2009 – Electric cables. Thermosetting insulated, armoured, fire resistant cables of rated voltage 600/1000V, having low emission to smoke and corrosive gases when affected by fire.Some circuits requiring an equivalent level of fire resistance need to be designed for larger cables than are found in BS 7629-1. Such circuits may be for the main emergency supply, fire fighting lifts,
sprinkler system and water pumps, smoke extraction fans, fire shutters or smoke dampers. These larger cables are standardized in BS 7846 which covers the size range and LSZH performance under BS 6724. Through the use of mica tape to supplement the insulation, the cables can pass BS 6387 CWZ and additionally the ‘standard’ or ‘enhanced’ grade as specified in BS 5839-1.
The cables are intended for use in fixed installations in industrial areas, buildings and similar applications, where maintenance of power supply during a fire is essential and where the evolution of smoke and corrosive gases must be kept to a minimum.
The circuit integrity performance under fire conditions is assessed on the basis of various tests where resistance to fire, resistance to fire with water, and resistance to fire with mechanical shock are assessed separately or in combination. The cables are designated by the following categories:
Category F1- resistance to fire alone
Category F2- resistance to fire, resistance to fire with water, resistance to fire with mechanical shock, assessed separately.
Category F3- resistance to fire with mechanical shock and water assessed in combination. The cables are wire armoured and
-two, three, four and five-core stranded copper conductor
-multicore auxiliary stranded copper conductor.
BS EN 60702 – Mineral insulated cables with a rated voltage not exceeding 750V.
BS EN 60702-1:2002 applies to mineral insulated general wiring cables with copper or copper alloy sheath and copper conductors and with rated voltage of 500V (light duty grade) and 750V(heavy duty grade). Provision is made for a corrosion resistant extruded outer covering over the copper sheath, when required. The standard sets out requirements for the optional outer covering, which includes equirements for halogen free covering and the thickness of the covering. The standard includes routine tests including a spark test on the outer covering. Sample tests includes such as flame retardance, emission of acidic and corrosive gases and smoke emission. Type tests such as fire resistance are included.
Mineral insulated cables are extremely resistant but rigid and a particular care has to be paid during installation to prevent moisture absorption by the mineral oxide.
500V grade cable includes the following conductor sizes:
- single and twin conductor cables up to 4mmsq csa
- three, four and seven conductor cables up to 2.5mmsq csa
750V grade cable provides for:
- single conductor cables up to 400mmsq csa
- two, three and four conductor cables up to 25mmsq csa
- seven conductor cables up to 4mmsq csa
- twelve conductor cables up to 2.5mmsq csa
- nineteen conductor cables up to 1.5mmsq csa
The fire related properties by the cable standards are summarised in the following table: