Page 39 - Pocket Guides

PG 21
PG 1-2
CABLE PASSING THROUGH OR OVER JOISTS
EXPLANATORY NOTES FOR CABLES INSTALLED UNDER A FLOOR OR
ABOVE A CEILING
1. Regulation 522.6.201 specifies a minimum depth of 50 mm from the top or bottom,
as appropriate, of a joist or batten to minimise the risk of a cable being penetrated by
a fixing (nail, screw or the like) that is used to fix the floorboards or ceiling boards to
the joist. Where the contractor suspects that a depth of 50 mm will not be sufficient,
which might be the case due to the length of the particular fixings, the cable must
be installed at an increased depth. Where a joist, due to its dimensions, does not
permit an increased depth (or the 50 mm previously mentioned), one (or more) of the
following methods should be used.
2. Regulation 522.6.204* specifies the use of cables complying with BS 5467, BS 6724,
BS 7846, BS 8436 and BS EN 60702-1, such as mineral insulated copper sheathed
or steel wire armoured (swa) cables. The intention of installing such cables is to
ensure that should a fixing penetrate a cable it cannot make contact with a live
conductor without first coming into contact with the earthed metallic covering,
thereby providing a direct path for earth fault current to flow so that automatic
disconnection of the circuit occurs. Also, Regulation 543.2.5 requires that where the
metallic covering of a cable is used as a protective conductor, the metallic covering
should satisfy the requirements of items (i) and (ii) of Regulation 543.2.2, relating to
electrical continuity and cross-sectional area, respectively.
3. Regulation 522.6.204 specifies conduit complying with BS EN 61386-21 and trunking
or ducting complying with BS EN 50085-2-1. The intention of installing these earthed
containment systems to enclose cables in floors and ceilings is to provide similar
protection as given in 2 (above).
4. The electrical industry recognises that steel having a minimum thickness of 3 mm
may be suitable to prevent penetration of a cable by fixings. However, where shot
fired fixings are used a 3 mm plate is unlikely to prevent penetration and a thicker
plate will need to be used. Metal and plastic capping is not of sufficient strength and
should not be used.
* The titles of the British Standards given in Regulation 522.6.204 can be found in
Appendix 1 of BS 7671.

Download Pocket Guides via the Customer Portal
www.my.niceic.com/login or www.my.elecsa.co.uk/login
© CERTSURE LLP 2018