British Standard BS 7671:2008
Requirements for Electrical Installations
IEE Wiring Regulations Seventeenth Edition
522.6 Impact (AG)
522.6.1 Wiring systems shall be selected and erected so as to minimize the damage arising from mechanical stress, e.g. by impact, abrasion, penetration, tension or compression during installation, use or maintenance.
522.6.2 In a fixed installation where impacts of medium severity (AG 2) or high severity (AG 3) can occur protection shall be afforded by:
(i) the mechanical characteristics of the wiring system, or
(ii) the location selected, or
(iii) the provision of additional local or general protection against mechanical damage, or
(iv) any combination of the above.
NOTE: Examples are areas where the floor is likely to be penetrated and areas used by forklift trucks
522.6.3 The degree of protection of electrical equipment shall be maintained after installation of the cables and conductors.
522.6.4 A wiring system buried in a floor shall be sufficiently protected to prevent damage caused by the intended use of the floor.
522.6.5 A cable installed under a floor or above a ceiling shall be run in such a position that it is not liable to be damaged by contact with the floor or the ceiling or their fixings. A cable passing through a joist within a floor or ceiling construction or through a ceiling support (e.g. under floorboards), shall:
(i) be at least 50 mm measured vertically from the top, or bottom as appropriate, of the joist or batten, or
(ii) incorporate an earthed metallic covering which complies with the requirements of these Regulations for a protective conductor of the circuit concerned, the cable complying with BS 5467, BS 6346, BS 6724, BS 7846, BS EN 60702-1 or BS 8436, or
(iii) be enclosed in earthed conduit complying with BS EN 61386 and satisfying the requirements of these Regulations for a protective conductor, or
(iv) be enclosed in earthed trunking or ducting complying with BS EN 50085 and satisfying the requirements of these Regulations for a protective conductor, or
(v) be mechanically protected against damage sufficient to prevent penetration of the cable by nails, screws and the like
522.6.6 A cable concealed in a wall or partition at a depth of less than 50 mm from a surface of the wall or partition shall:
(i) incorporate an earthed metallic covering which complies with the requirements of the Regulations for a protective conductor of the circuit concerned, the cable complying with BS 5467, BS 6346, BS 6724, BS 7846, BS EN 60702-1 or BS 8436, or
(ii) be enclosed in earthed conduit complying with BS EN 61386 and satisfying the requirements of these Regulations for a protective conductor, or
(iii) be enclosed in earthed trunking or ducting complying with BS EN 50085 and satisfying the requirements of these Regulations for a protective conductor, or
(iv) be mechanically protected against damage sufficient to prevent penetration of the cable by nails, screws and the like, or
(v) be installed in a zone within 150 mm from the top of the wall or partition or within 150 mm of an angle formed by two adjoining walls or partitions. Where the cable is connected to a point, accessory or switchgear on any surface of the wall or partition, the cable may be installed in a zone either horizontally or vertically, to the point, accessory or switchgear. Where the location of the accessory, point or switchgear can be determined from the reverse side, a zone formed on one side of a wall of 100 mm thickness or less or partition of 100 mm thickness or less extends to the reverse side.
522.6.7 Where Regulation 522.6.6 applies and the installation is not intended to be under the supervision of a skilled or instructed person, a cable installed in accordance with Regulation 522.6.6 (v), and not complying with Regulation 522.6.6 (i), (ii), (iii) or (iv), shall be provided with additional protection by means of an RCD having the characteristics specified in Regulation 415.1.1.
522.6.8 Irrespective of the depth of the cable from a surface of the wall or partition, in an installation not intended to be under the supervision of a skilled or instructed person, a cable concealed in a wall or partition the internal construction of which includes metallic parts, other than metallic fixings such as nails, screws and the like, shall:
(i) incorporate an earthed metallic covering which complies with the requirements of these Regulations for a protective conductor of the circuit concerned, the cable complying with BS 5467, BS 6346, BS 6724, BS 7846, BS EN 60702-1 or BS 8436, or
(ii) be enclosed in earthed conduit complying with BS EN 61386 and satisfying the requirements of these Regulations for a protective conductor, or
(iii) be enclosed in earthed trunking or ducting complying with BS EN 50085 and satisfying the requirements of these Regulations for a protective conductor,
(iv) be mechanically protected sufficiently to avoid damage to the cable during construction of the wall or partition and during installation of the cable, or
(v) be provided with additional protection by means of an RCD having the characteristics specified in Regulation 415.1.1
NOTE: If the cable is installed at a depth of 50 mm or less from the surface of a wall or partition the requirements of the Regulation 522.6.6 also apply.