2. The types of cables specified in paragraphs (c) and (f)
   of Regulation 84 of these regulations may, with the written
   permission of the electrical supply authority, be used in
   situations where conduit would be subject to corrosive action,
   if the wiring is in full view, conductors are “looped in,” and
   junction boxes or fittings are not used.

CLASS R.—ARMOPRED CABLES.

1. Armoured cables such as are specified in paragraphs (a),
   (e), and (i) of Regulation 84 of these regulations may be used
   without the further protection of conduit or casing, provided
   that they are installed in accordance with paragraphs (d)
   and (h) of clause 2 of the conditions governing the use of
   Class L cables, and paragraphs (a), (b), (e), and (f) of the
   conditions governing the use of Class S cables.

2. In addition to the foregoing conditions, the following
   shall apply to the use of Class R cables, namely—
   (a) Effectual means shall be taken to ensure that all
   metallic envelopes of cables are efficiently earthed and
   made electrically continuous throughout their length
   by means of soldered joints, or, alternatively, by
   bonding-clamps specially designed for the purpose of
   forming part of joint-boxes and similar fittings in
   which the cables terminate.
   (b) The electrical resistance of the metallic envelope of
   cables in a complete installation, measured between
   such envelope at a point near the main switch and
   any other point of the installation, shall not exceed
   2 ohms.

CLASS S.—CABLES COVERED WITH TOUGH RUBBER COMPOUND.

1. Cables protected in accordance with paragraph (g) of
   Regulation 84 of these regulations may be used without
   the further protection of conduit or casing, provided that they
   are installed in accordance with paragraphs (c) and (d) of
   clause 2 of the conditions governing the use of Class L cables,
   and provided that—
   (a) They are secured at intervals (sufficiently short to
   prevent appreciable sagging of the cable) by clips,
   saddles, or clamps constructed of such material as
   will not be liable to set up an electrolytic action, and
   having smooth or rounded edges which will not indent
   or damage the sheathing.
   (b) When vertical, they are fixed by the same means, with
   supports at the same intervals as when horizontal,
   unless they be inaccessible, when a length not
   exceeding 10 ft. may be allowed between the supports,
   if the upper support firmly grips the cable, and that
   where there is a change of direction from horizontal
   to vertical they are brought over a rounded support
   of a radius not less than six times the external
   diameter of the sheathing.
   (c) Where laid across the ceiling-joists at any angle, they
   are attached to the side of soft wood strips of not
   less than 1 in. by 1 in. dimensions; that where laid
   parallel with the joists they are attached to the side
   thereof, and that clips or saddles are not spaced more
   than 18 in. apart.
   (d) They are protected by wood or metal casing or conduit
   where exposed to mechanical injury, as on walls
   up to a distance of 6 ft. from the floor; and that
   clips or saddles are spaced not more than 9 in.
   apart on ceilings, or more than 12 in. apart on
   vertical runs.
   (e) If liable to mechanical damage they are adequately
   protected, having regard to the nature of their
   sheathing or casing.
   (f) In damp situations, and where exposed to the weather,
   the saddles and fixings are of non-rusting material.
   (g) When passing through steel or iron structural work,
   the holes through which they pass are bushed to
   prevent abrasion.
   (h) Under no circumstance shall they be used to pass through
   party walls, or as service mains, or for power or on
   pressures exceeding 250 volts to earth.
   (i) When under floors and not running parallel to the
   joists, they may be without support from joist to
   joist to a distance not exceeding 18 in., and all
   floor-boards covering the wiring shall be securely
   screwed down in such a manner that they will not
   damage the cable and so that they can be removed
   for inspection. When running parallel with joists
   they may be laid flat on the ceiling.
   (j) At all outlet points the sheathing is efficiently anchored
   before the base-block or other device is mounted.

2. Connection - boxes of types approved by the Chief
   Electrical Engineer may be used,

CLASS T.—SCREWED CONDUITS.

All classes of cable specified in Regulation 84 of these regulations may be enclosed in screwed steel conduits, provided that the conduits are installed in accordance with paragraphs (d) and (h) of clause 2 of the conditions governing the use of Class L cables and in accordance with paragraphs (e) and (f) of the conditions governing the use of Class S cables, and also provided that—
(a) The conduits are made in accordance with British Standard Specification No. 31 and are of heavy gauge, and that the conduit fittings are to British Standard Specification No. 31, but terminal fittings may be used in which the length of thread for conduit is less than that specified in the said specification, in which case either a taper male thread or lock-nuts shall be used.
(b) The conduits are mechanically and electrically continuous across all joints therein, and are earthed in accordance with Part XI of these regulations.
(c) The electrical resistance of the conduit in a complete installation measured between the conduit at a point near the main switch and any other point of the installation does not exceed 2 ohms.
(d) Where liable to condensation drip-outlets not exceeding ⅛ in. diameter and not less than ⅛ in. diameter are provided at the lowest point of each circuit to permit the exit of moisture.
(e) The conduits of each circuit are erected complete before the cables are drawn in, that conduits of less than 1 in. diameter are secured at least every 4 ft., and conduits of 1 in. diameter and over are secured at least every 6 ft. (except where they are used between supports placed more than 6 ft. apart, in which case they shall be secured to the satisfaction of the Authorized Inspector), and that all conduits are secured by means of approved saddles, which in the case of surface work must be fixed with screws.
(f) Bell mouths or other approved metal outlets are fitted to the ends of all conduits to prevent abrasion of the covering of cables emerging therefrom, and that galvanized conduit at all external outlet-points is set down not less than 45°, and terminates with a non-corroding bell-mouth.
(g) The ends of conduits where terminating at accessories and fittings are screwed thereto, or secured with lock-nuts if screwing is impracticable, or provided with metal outlet-boxes, save that metal outlet-flanges approved by the Chief Electrical Engineer may be used in place of outlet-boxes, except in the case of buildings of concrete or brick; and provided that the ends of all conduits where terminating at tees, elbows, junction-boxes, or other outlet-points are reamed out and do not project into the box beyond the thread of the box or the lock-nut.
(h) All elbows and tees are of the inspection type, and that all bends have a radius not less than two and a half times the outside diameter of the conduit save that—
(i) At the ends of conduits immediately behind fittings or accessories plain conduit fittings may be used.
(ii) In surface wiring where the conduit turns to pass through a wall a plain elbow may be used if the conditions are such that the use of an inspection elbow or normal bend would be impracticable.
(iii) In an inaccessible position such as in a hollow partition a plain elbow may be used if it is impracticable to use a normal bend.
(i) In damp situations where exposed to the weather (even if only during building-construction) or the action of corrosive fumes or liquids, conduits together with their fittings are galvanized.
(j) In all cases where galvanized conduit is used the threads where the galvanizing has been removed are adequately protected by painting with white-lead, red-lead, or graphite pipe-jointing compound before screwing into fittings.
(k) Galvanized conduits are not buried in damp ground or in ground likely to contain acids.
(l) Where it is necessary to enclose wires in metal pipes in damp ground, galvanized water-pipe (free from internal fins and burrs) or other metal approved by the Authorized Inspector is used.
(m) Where it is necessary to enclose wires in metal pipes in ground likely to contain acids the wires are enclosed in lead pipes.