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.