Trunking is to be manufactured from either mild steel or PVC and shall confirm to BS EN 50085: Part 1, BS EN 50085: Part 2-1, BS 4678: Part 4 and BS 4678: Part 2. Cable trays shall be manufactured from mild steel. Mild steel trunking and cable trays shall be hot dip galvanised. Where the trunking or cable trays are cut, drilled or where the galvanising is damaged in any way the surfaces shall be adequately treated to restore them to the original galvanised standard. The number of cables installed in the trunking shall not exceed that recommended in BS 7671 (IEE Regulations), and the resulting space factor shall not exceed 45%. The fixing of trunking and cable trays and the installation of cables into or on trunking and cable trays shall be carried out using the manufacturer's approved accessories and fixings only. Such accessories and fixings shall be either manufactured from non- corrodible materials or supplied suitably coated to render them non-corrodible. 3.3.5. Conduit Systems Conduits for occupied areas to be concealed; conduit for unoccupied areas to be surface mounted and GS conduit pipe for Plant-Rooms. Conduits within buildings and structures shall be extra-super-high-impact heavy-gauge PVC-u conduit, installed with solvent welded joints and shall be installed with screwed fittings. Conduit systems shall conform to BS 4607: Part 1, BS 4607: Part 5, BS EN 61386: Part- 1, BS 4568: Part 1 as appropriate, and the number of cables installed shall not exceed those recommended in BS 7671 (IEE Regulations). The conduit system where it passes through the building structural expansion joints, suitably rated/sized expansion couplers shall be used in order to absorb the expansion/contraction. Fixings and accessories associated with conduit systems shall be either manufactured from non-corrodible materials or suitably coated to render them non-corrodible. No conduit shall be smaller than 20 mm diameter. Cable runs shall be continuous throughout. Jointing shall not be carried out in conduits or at drawing points under any circumstances. Draw-in boxes shall be spaced so that there is not more than two solid bends, or their equivalent, or more than nine metres of straight run between draw-in boxes. Flexible conduit for connection to mechanical equipment. 3.3.6. Cables Laid Directly in Ground The Contractor shall be responsible for all work associated with cabling including trenching, ducting under roadways and backfilling of trenches. Cables shall be laid at a depth of not less than 500 mm or not more than 1,000 mm below the surface of the ground. The bottom of the trench and the first 250 mm of backfill shall be fine sand free of stones or other sharp objects. Where cable trenches pass through stone fill, the cable shall be laid on an 80 mm bed of sand. After laying, the cable shall be covered by a further layer of sand to a depth of 80 mm above the top of the cable. Where sand is likely to leach away, a suitable membrane shall be fitted. Page 85