If casing be used, it shall be of hard teak wood or PVC or heavy gauge conduit pipes.
Each conductor shall be laid in separate groove, unless previous permission is obtained from the Chief Engineer (Electrical) or the Electrical Inspector concerned to vary this condition. In no circumstances wires of unlike polarity shall be laid in the same groove, nor the wires of the same polarity belonging to the different circmts (A), (B) or (C). The cover shall be secured with screws. Casing shall not be used where it is liable to inju1y from weather or leakage of water, nor shall it be recessed into plaster.
50. Metallic tubillg for Jfecl1a11ica/ Protection -Where on pipe or tube is used as a mechanical protection, it shall be bushed where necessary and properly bushed inspection boxes shall be used. All metallic tubing shall be efliciently earthed and shall be provided screw joints or other means of ensuring a good and permanent electrical connection which must be continuous with boxes and other fittings.