Busbars shall conform to BS 159, BS 1432 and BS 1433, and shall be tinned hard drawn high conductivity copper with an adequate uniform rectangular cross section to carry continuously their rated current without overheating. They shall be rigidly mounted on non-hygroscopic insulators so as to withstand any mechanical stresses to which they may be subjected under maximum fault condition.
Busbar sizes must not be less than that specified in the Drawings. However if the busbar sizes are not specified, then the busbar rating shall be based on a current density of not more than 1.5 A/sq. mm. In any case, the busbars rating shall not be less than the rating of the incoming switchgear. All busbars, whether horizontal or vertical, shall be of the same size.
The main busbars shall be run for the full length of the switchboard without reduction in size. Neutral busbar shall be of full size and full length as the phase busbars. Connections shall be made up with bronze or other copper alloy bolts and nuts utilising tension washers on both outer faces. Where multiple parallel bars are used, they shall be separated by tinned copper spacers at spacing equal to the busbar thickness.
The main busbar shall be arranged in a horizontal plane in the order redyellow- blue-neutral from back to front. On each panel connections should be red-yellow-blue-neutral. Busbars shall be painted at appropriate points with colours red, yellow, blue and black to denote the phases. Tinned copper earthing bar of cross sectional area not less than 50 mm x 6 mm shall run along the switchboard for its entire length. This main earthing bar shall be fastened and bonded at the base to each vertical frame member of the switchboard. At least one earthing bar of similar cross sectional area shall run the full height of the switchboard and connected to the main earthing bar.
All earthing bars shall be identified with green and yellow (twin-coloured) colour. Connections from busbars to the switchgears shall be effected by means of copper conductors securely clamped to the busbars and colour coded to identify the phase and neutral conductors. Copper conductor either bare tinned busbars or insulated cable shall be rated in accordance with the current rating of the switchgear. Neutral conductor shall be of full size as phase conductor. Coloured cable sleeve shall be shrouded for cable end termination.