‘U’-SHAPED WITH OVERLAPPING FRONT COVER TYPE

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8.2 ‘U’-SHAPED WITH OVERLAPPING FRONT COVER TYPE
For the ‘U’ shaped channel type of busbar trunking, the trunking channel shall be of folded sheet steel of not less than 2.0 mm thickness. The front covers shall be of folded sheet steel of not less than 1.5 mm thickness. Unless otherwise instructed, the front covers shall be manufactured in maximum length of not more than 1200 mm and shall be so designed as to provide access to the busbar at each floor landing of the riser duct after the sealing of the floor of the riser duct. Sheet steel used for fabricating the trunking channels and the covers shall undergo derusting treatment, painted with a primer and finished in stoved enamel of standard orange colour.
The trunking shall be supported rigidly by external fixing angel brackets of spring loaded supports at intervals no greater than 2000 mm for vertical runs and no greater than 1000 mm for horizontal runs so that the trunkings will not be in contact with the wall or floor slab surfaces. The brackets shall undergo de-rusting treatment, painted with a primer and finished in orange enamel. For busbar risers, the trunkings shall be provided with end sections capable of supporting the whole busbar riser and if necessary another reinforcement section shall be installed.
Busbars shall be of hard drawn high conductivity copper to BS 159, BS 1432 and BS 1433. The busbar current rating shall not be less than that specified in the Drawings basing on current density of not more than 1.5 A per sq. mm. If the claimed current density is higher than that specified, test certificate shall be furnished to substantiate the claim. The busbars shall be totally enclosed in the trunking and shall be supported within the trunking by high grade, nontracking, unbreakable polyester fibre insulators at intervals of not more than 250 mm.
Expansion joints made of corrugated pieces of copper or any other approved type, shall be provided in the busbars for every interval of 20 m at maximum and at the end of each busbar. At the busbar joints, sufficient length of adjacent sections shall overlap each other so as to provide rigidity and strength.
Wherever busbar passes through a floor or a fire resistant wall, internal fire resisting barrier shall be provided. The fire-resisting barrier shall be of nonhygroscopic material with minimum 2-hour fire rating and approved by Jabatan Bomba Dan Penyelamat Malaysia.

In addition, the floor openings and wall openings shall be sealed according to the appropriate degree of fire resistance. In the case of service duct, similar internal fire resisting barrier shall be provided at each floor level.
Tap-off units and other accessories shall be provided as specified. They shall be of either plug-in type or bolted type and shall be suitably earthed. Where fuses are used, they shall be of BS type. Earth continuity of the trunking shall be provided by a continuous length of tinned copper strip of dimension not less than 25 mm x 3 mm fitted to the external of the trunking at suitable intervals by means of brass bolts and nuts.


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