8.1 PRE-ASSEMBLED, TOTALLY ENCLOSED TYPE (BUS DUCT
For the pre-assembled type of busbar trunking (bus duct), the housing shall be of galvanised sheet steel of not less than 1.5 mm thickness finished with epoxy dry-powder and oven baked enamel grey. Fire-resisting barriers shall be included as an integral part of each bus duct length and fitting. The maximum length of the bus duct shall be not more than 3000 mm and the tap-off openings for plug-in units shall be provided at every interval of not more than900 mm. Unless otherwise specified, the degree of protection shall be IP42 for indoor installation and IP65 for outdoor installation in accordance to IEC 60529.
Busbars shall be of hard drawn tinned 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 fully insulated over its entire length except joint parts and totally enclosed in the housing. The insulation shall be seamless and also be flame-retardant.
Earth continuity of the bus duct 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 bus duct. The plug-in unit shall be mechanically interlocked with the busway housing to prevent installation or removal of plug-in unit while the switch in ON position. Plug-in unit enclosures shall make positive earth connections to the bus duct housing before contacts are made with the busbars.
Expansion joints shall be provided for every interval of 30 m at maximum, and at the end of bus duct end box unit shall be provided. Bus duct joints shall have sufficient contact length of adjacent sections so as to provide rigidity and strength. A spring material shall be used in jointing so as to ensure a constant contact pressure. All joint units, tee and elbow units, offset and combination elbow units, flanged end-feed units, expansion joint units and end joint units for the bus duct system installation shall be the type manufactured and supplied by the same bus duct manufacturer.
The bus duct system shall be supported rigidly and adequately by external spring hangers mounted on channel base. Th bus duct system shall be supported at intervals no greater than 3000 mm for vertical runs and no greater than 1500 mm for horizontal runs so that the bus duct will not be in contact with the wall or floor slab surfaces. The spring hangers shall be supplied by the bus duct manufacturer. The floor openings and wall openings where bus duct passing through shall be sealed with fire-resisting material according to the appropriate degree of fire resistance to the approval of the Jabatan Bomba Dan Penyelamat Malaysia.