Remerciez-le!

Remerciez @Admin pour avoir partagé cet document gratuitement, de la manière la plus simple, en partageant sur les réseaux sociaux.

POCKET GUIDE 21 Cables passing through or over joists Based on information as a

POCKET GUIDE 21 Cables passing through or over joists Based on information as at September 2010 www.niceic.com © Pocket Guide 21 09/10 ii iii iv i v Ceiling board Minimum 50 mm to top or bottom, as approriate, of joist Cables that pass through or over timber joists can be particularly vulnerable to damage, which can lead to the dangers of electric shock or fire unless suitable measures are taken. In order to protect against these dangers, Regulation 522.6.5 of BS 7671: 2008 requires a cable installed under a floor or above a ceiling to be run in such a position so that it is not liable to be damaged by contact with the floor, the ceiling or any of their fixings. The Regulation also requires that where a cable has to pass through a timber joist within a floor or ceiling construction or through a ceiling support (e.g. under floorboards), the cable shall: be at least 50 mm measured vertically from the top or bottom, as appropriate, of the joist or batten, or incorporate an earthed metallic covering which complies with the requirements of BS 7671 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 be enclosed in earthed conduit complying with BS EN 61386 and satisfying the requirements of BS 7671 for a protective conductor, or be enclosed in earthed trunking or ducting complying with BS EN 50085 and satisfying the requirements of BS 7671 for a protective conductor, or be mechanically protected against damage sufficient to prevent penetration of the cable by nails, screws and the like. The five conditions are illustrated below: i ii iii iv v NOTES: 1. The titles of the British Standards listed in Condition are given in Appendix 1 of BS 7671. 2. Explanatory notes on the five conditions are provided on the reverse of this guide. ii For further copies of this guide telephone 0870 0130382 or e-mail customerservice@niceic.com © Pocket Guide 21 09/10 POCKET GUIDE 21 www.niceic.com Cables passing through or over joists Explanatory notes: The specified minimum depth of 50 mm from the top or bottom (as appropriate) of a joist or batten is intended to avoid the cable from being penetrated by a nail, screw or the like that is used to fix the floorboards or ceiling boards to the joist. However, if the electrical installer believes that a 50 mm depth will not be sufficient for this purpose, due to the length of the nails etc., then either the cable must be placed at a sufficiently increased depth to avoid penetration, or one of the other conditions, – , must be complied with. The use of a cable incorporating an earthed metallic covering, such as mineral insulated copper sheathed (MICS) or steel wire armoured (SWA) cable, is intended to ensure that a nail, screw or the like cannot make contact with a line conductor of the cable without first coming into good electrical contact with the earthed metallic covering (by piercing), thereby providing a direct path for earth fault current to flow to cause automatic disconnection of the circuit concerned. Regulation 543.2.5 requires that where the metallic covering of a cable is used as a protective conductor, the metallic covering shall satisfy the requirements of items (i) and (ii) of Regulation 543.2.4, relating to electrical continuity and cross sectional area, respectively. Enclosing a cable in earthed conduit in accordance with BS EN 61386 effectively provides the same method of protection as a cable incorporating an earthed metallic covering, as in condition . Enclosing a cable in earthed trunking or ducting in accordance with BS EN 50085 effectively provides the same method of protection as a cable incorporating an earth metallic covering, as in condition . A steel plate at least 3 mm thick (covering the full width of the joist) will generally be sufficient to prevent penetration of a cable by a nail, screw or the like that is used for fixing the floorboards or ceiling boards. However, in situations where shot fired fixings might be used, even a 3 mm plate would not necessarily prevent penetration, and would therefore be unsuitable. It should be noted that the use of some proprietary metal plates sold to protect cables are too thin to prevent penetration by a nail or similar, or even make the person driving in the fixing aware of the metal plate. Condition i Condition ii Condition iii Condition iv Condition v ii v ii ii uploads/Ingenierie_Lourd/ cables-passing-through-or-over-joists-bs-7671-2008-requires-a-cable-installed-under-a-floor-or-above-a.pdf