CABLING & CABLE MANAGEMENT SUPPLEMENT FEATURE 18th Edition: Setting the record straight


There is still some speculation as to what exactly the 18th Edition of the IET Wiring Regulations mean, leading to many varied and confusing interpretations about supporting wiring systems


J


ohn Brodie, product manager for fastenings and fixings at


HellermannTyton is keen to dispel these misinterpretations and set the record straight. To understand what additional support


is required for wiring systems, we must first understand what has changed in the regulations: Firstly, there is the location - the


scope of where additional support is required is now much greater than it was previously. Where the previous wiring regulations stated ‘escape routes’ it now states ‘access or egress routes’, meaning both entry routes in and exit routes out of the building are covered. The 18th Edition is also explicit that


plastic clips should not be used as the sole or ‘main’ support for cables. In addition to this, strong reference is made to the spacing of the metallic clips and fixation methods. Finally, there is specific reference made to cable trays and baskets, stating that


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these methods of cable management meet the regulations. What is clear from these changes is that


the scope of the new regulations is wider than in the 17th Edition 3rd Amendment, specifically where reference is made to both entry routes in and exit routes out of the building. This reference combined with explicitly requiring metallic fixing is to reduce the risk of cables causing an obstruction - both to the residents of buildings as well as to first responders. When fixing cables to exposed surfaces


vertically and horizontally, the spacing of metal fixings should be approximately 250-400mm. HellermannTyton does not recommend that plastic fixings are used as the only method of fixing, and should only be used in addition to sufficient metal fixing. Where changes have been made to


include cable trays and baskets it is recommended that larger cables and cable bundles are fixed within a cable basket or tray. Using metal fixings, such as stainless steel cable ties in conjunction with cable


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trays and baskets, ensures maximum compliance with the 18th Edition to reduce risk of cables causing obstruction in the event of a fire. In addition to BS 7671, there are


other standards to consider for new installations. BS 5839 gives recommendations for fire detection devices and fire alarm systems for buildings and BS 5266 gives recommendations for emergency escape lighting. Both standards recognise the danger


of collapsing cable supports in a fire, a danger which will be decreased with the introduction of the requirement of metal fixings. Fire performance cables must maintain


their function for a minimum of 120 minutes at temperatures up to 970 degrees. HellermannTyton recommends that fire resistant cable is supported using exclusively metal fixings.


HellermanTyton hellermanntyton.co.uk


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