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With Reference to

Sergio Fernandez



BS 7671 cable reference method wiring codes include reference methods A, B, C, D, E, F, G, 100, 101, 102 and 103.
Methods 100, 101, 102 and 103 refer to twin and earth cables installed in thermal insulation.

Now that Conduit, Tray/Non-perorated Tray, Ducting and Trough (other versions of containment are also available) are being made from GRP or can be made from GRP does BS 7671 reference/referencing method need updating or clarifying? What about BS7671 Part 5 or GN1 (Guidance Note 1 )


Points to consider


Yield strength of the GRP in lets say tray vs metal tray
Heat dissipation of the GRP vs that of metal or plastic conduit
Grouping factors
GRP Self extinguishing from fire vs PVC conduit with a specific focus on premature collapse of containment systems causing possible entanglement issues for EFR (Emergency First Responders) or fire spread.

Will some people just stick with the fact that trunking is trunking and state
Reference Method B = Enclosed in conduit or trunking on a wall.

It is worth or does it need highlighting to the industry.  During Selection and Erection maybe they should consider GRP products.   Another caveat here, one person/small operation they will probably be Designer, Installer, Commissioner and Tester of that install, in large companies this could be done my multiple teams of people.




As always please be polite and respectful in this purely academic debate.





Come on everybody let’s help inspire the future.

  • We've it comes to conduit and trunking (and indeed capping) we've used the same tables for both Steel and PVC for many years without any apparent problems - so while there is obviously poorer heat dissipation through PVC, there must be adequate margins within the tabulated numbers that we don't have to worry about it.

    I'd suspect that GRP tray etc would be likewise - i.e. use the traditional installation methods/ratings for "tray" and all should be well - if anything the difference material would have less of an effect than it would for conduit.

    I'd agree that GRP is going to be a lot less effective for preventing premature collapse in the case of a fire - but there will be methods of working around that where needed (e.g. many products have appeared over the last decade or so to restrain cables in PVC mini and maxi trunking and conduit - everything from fire clips to white painted steel saddles, or just existing designs of stainless steel cable ties).

       - Andy.

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