Long shot - anyone have a copy of the WireRegs/Commentary-UpdateApr04.pdf

I think I might have a copy on a HDD which came out of an expired PC.

If nobody else has come up with a copy by the weekend, I'll see if I can find it and stick it in a caddy and have a search.

This sort of consideration Mike?


"Has some tables that suggest that at full all day loading, to a 70 degree core temp, one might expect a 23 year life before the plastic cracks and loses its integrity.

I suspect that much more realistic is full load for 8 hours a day (69 hour life) or even operation at at less than 70 degree core temp (most domestic lighting circuits for example a very under-run) and then one has a doubling in life time for every 6 or 7 degrees, mind you for PVC it is all based on extrapolation from a test 5000 hour life at 101 degrees, and 20000 hour life at 89 degrees. I suspect that local instalation details (like 'exposed to sunshine', or as norman has pointed out, 'touching heating pipes' will be dominant in many parts of a real installation.)

I expect many well done installtions to outlast the building on that basis.. (average building life in the UK is a few hundred years at present, but that number is not real, and is is only becasuse we are currently building faster than we are demolishing..)"


regards Mike


One cable maker's view...

https://www.whyprysmian.co.uk/cable-design.html


Z.

Whilst this might provide some insight, it cannot in any way be described as definitive. Plasticised PVC is not a single material with constant properties, every stage of its manufacture and processing will change the aging characteristics in unknown ways. It would appear that cracking is not the major failure mechanism, as it is for uPVC, and from samples of cable from the first day that PVC was used, it appears to have a virtually unlimited life as cable sheaths or primary insulation in most installations. UV does cause cable damage after a long period in PVC without suitable blocking pigment, but is usually powdering of the surface, caused by de-polymerisation and breaking of the polymer chains. It takes a very long time for the sheath to disappear and for the primary insulation to be attacked. The main effect of long term heat is probably slow loss of the plasticiser, which makes the cable more rigid, and possibly susceptible to mechanical movement and could cause cracking if the cable is flexed. However this would be unusual in the fixed wiring installation. The best way to check the cables is undoubtedly inspection and perhaps laboratory examination if the application is particularly critical.

The I.E.T's Guidance note 6 (17th edition) on page 21) says that the advice from the British Cables Association on cable life is "Estimating the life of a cable can only be approximate: There is no definitive simple calculation method that can be used to determine the life expectancy of a fixed wiring cable. (As many factors are involved).


9.5.3 refers to ascertaining cable working temperature ...

https://books.google.co.uk/books?id=qLekBAZUJloC&pg=PA169&lpg=PA169&dq=wiring+regs+commentary+update+2004&source=bl&ots=nNe9goe5OR&sig=ACfU3U1DFxUdPja2z-6dBbeEDVDGgbLtBg&hl=en&sa=X&ved=2ahUKEwiUyaqG7svoAhVQasAKHfTUCDEQ6AEwCXoECAsQLw#v=onepage&q=wiring%20regs%20commentary%20update%202004&f=false


Z.

Hi Mike. Our head of technical regulations says: 

Information on aging of cables can be found in “Commentary on IET Wiring Regulations 17th Edition (BS 7671:2008+A3:2015 Requirements for Electrical Installations), 7th Edition”. This publication was not updated to BS 7671:2018 but the information on aging of cables, page 104, clause 6.1.3, remains current; available here:

https://shop.theiet.org/commentary-on-the-iet-wiring-regulations-bs-7671-2008-2015


Mark Coles

Head of Technical Regulations

The IET


Hope that helps!

Thank you for that - I have now been shown a copy of the book version, which looks to have the same technical content as the web article that has been moved,  just some different introduction to what I recall and re-pagination.

I suspect the web article was intended to be an explanation of what is in the new book'  `and at the time it was new.

Is Paul Cook planning a commentary on the 18th? I really liked the guy. Excellent explanations.

Back when we printed out amendments and stuck them in our books, I found the original PDF printed out and stapled into my old copy of Commentary on IEE Wiring Regs 16th Edition BS7671: 2001.


See file attachment below