18th Edition Cable Fixings [A Clear Guide to selecting Fire Resistant Cable Fixings]
It has been over 2 years since the BS 7671:2018 18th edition of the Institution of Engineering and Technology (IET) wiring regulations came into force but there are still those in building services that are not aware of how to correctly select a cable fixing in-line with the standard.
What is the 18th Edition Cable Fixings wiring regulation?
18th Edition Wiring Regulations and Cable Supports BS7671:2018 is the 18th edition of the IET wiring regulations and the British Standard covering the design, installation, testing and inspection of electrical installations.
The 18th edition came into force from 1st January 2019 and applies to all fixed wiring installations designed from this date. Background In response to a number of fatal, fire related incidents where persons, including fire fighters, have been entangled by falling cables, the 18th edition has introduced significant changes to the way that cables are fixed.
The intent of this regulation is to prevent the possibility of cables collapsing prematurely in the event of a fire and becoming a hazard to evacuation and fire-fighting.
The Regulation Chapter 52 Selection and Erection of Wiring Systems Regulation 521.10.202 states:
‘Wiring systems shall be supported such that they will not be liable to premature collapse in the event of a fire’ – the 18th edition introduction makes clear this now applies throughout the installation and not just in escape routes as in the previous edition. The following notes to the regulation explain:
Note 2: Cables installed in or on steel cable containment systems are deemed to meet the requirements of this regulation.
Note 3: This regulation precludes, for example, the use of non-metallic cable clips or cable ties as the sole means of support where cables are clipped direct to exposed surfaces or suspended under cable tray, and the use of non-metallic cable trunking as the sole means of support of the cables therein.
Note 4: Suitably spaced steel or copper clips, saddles or ties are examples that will meet the requirements of this regulation.
How to select the correct cable fixing?
Cable Ties – most metal cable ties being used are 316 grade stainless steel, which were designed for use in harsh environments. However, these are costly, hence we launched a more economically priced steel cable tie in different sizes. They can be used for individual cables or cable bundles and suitable for use internally and externally.
Don’t forget that tensioning tools are available. They are designed to neatly cut-off excess metal tie.
Cable Mounts – When replacing plastic tie mounts, there are a few options depending on the method of installation and the size of cable being fitted. Screw or adhesive-fixed mounts can be replaced with a like-for-like metal equivalent. For faster installation, the metal push mount is ideal, it is simply pushed into a 6mm hole, so the likelihood of using incorrect fixings is removed. Our patent pending firesafe tie mount can be used with all cordless nailing tools – the snap-off tab for holding and positioning the mount during installation means there’s no need to change noses.
Cable Clips – Metal versions of the traditional-style nail-fixed clip are available and metal U and F clips can be used to secure cables within plastic trunking or as a standalone fixing. Safe D U clips can be used for securing cables to walls and ceiling voids whilst the Safe D F clips can be easily folded for securing individual cables or cable bundles to walls and ceilings. Remember to fix the D F clip with an all-metal fixing. Single and double metal stag clips are quick and easy to install and are ideal for T&E, FP and alarm cables.
Cable Harness – Metal cable clasps are a cost-effective way of installing cable bundles without the need for cable containment.
They are available in different sizes for either wall or ceiling mounting, cables can be easily added or removed during the installation process.
Are Plastics Banned?
Plastic cable fixings and plastic cable management have not been banned. They are still a cost-effective way of managing cables. It’s just that they can no longer be used as the sole method of support. Plastic cable ties and clips and plastic cable supports must all be adequately supplemented with metal supports.
Once you have selected the most appropriate cable fixings, be mindful that the screws and expansion plugs should also be compliant.
This guide is given as helpful information for specifiers and installers of electrical systems in the context of cable supports and fixings that satisfy the requirements of the 18th Edition Wiring Regulations.
The following guide will provide you with:
- Provides a brief overview of 18th Edition Wiring Regulations and Cable Supports
- How to apply the regulation in practice
- Understanding which cable supports are suitable
- Identifying the melting points of different wiring system materials
- Knowing the correct spacing of cable supports
- Choosing the right fixings for fire-resistant cable
For further information on our 18th edition range of cable accessories contact MIDFIX.