An employer or user shall cause -
(a) roofs, gutters, downpipes and waste pipes on premises to which electrical energy is supplied to be earthed, except -
(i) where the operating voltage does not exceed 50 V;
(ii) roofs made of non-conductive material or metal roofs covered by non-conductive material;
(iii) gutters, downpipes and waste pipes made of non-conductive material or gutters and downpipes attached to a metal roof which is covered by non-conductive material;
(iv) roofs, gutters, downpipes and waste pipes on premises which receive electricity by means of underground service connections: Provided that the connection is to the conductive structures;
(b) all accessible metallic parts of electrical machinery that, though normally not forming part of an electrical circuit, may become live accidentally, to be protected by an insulating covering or to be otherwise enclosed or to be earthed and the resistance of the earth continuity path shall not exceed 0,2 ohm, except -
(i) metal in earth-free situations, other than runs of metal wireway, and the close-fitting metal sheathing and armouring of cables;
(ii) short separate lengths of heavy-gauge metal wireway used for the mechanical protection of cables where such cables are not used in the secondary circuits of discharge luminaire installations;
(iii) short, unexposed separate lengths of metal wireway used for the mechanical protection of insulated wiring passing through walls, floors, partitions or ceilings;
(iv) metalwork of fixed electrical machinery where such metalwork is more than 2,4 m above the floor: Provided that this exception shall not apply where such metalwork is situated in any position likely to become damp, or in an elevator shaft, or near rotating machinery, or in contact with a wall, ceiling or other support constructed of or covered with conducting material;
(v) metal parts of electrical machinery where such parts are enclosed or shrouded by insulating material so that such metal parts cannot be touched;
(vi) cleats, clips, saddles, clamps of other devices for fixing wireways and cables;
(vii) shades, reflectors and guards supported on lamp holders or discharge luminaires;
(viii) lamp caps;
(ix) metal parts of or screws in or through non-conducting materials which are separated by such materials from current-carrying parts and from earthed non-current-carrying parts in such a way that in normal use they cannot become live or come into contact with earthed parts.
