jim_in_sussex wrote:


The maximum working temperature for normal twin & earth PVC cable is
70deg C - a rise of 40deg above an assumed max ambient of 30deg. If
ambient is regularly over 30deg C either because you're in a warm
country or the cable is running through a hot spot (eg near CH) then
the max cable amps permitted is reduced. A cable running at a
constant 70deg will have a relatively short life - a few years, no
more.

Actually it's taken to be 20 years - running at 70degs is "legitimate"
long-term loading (though most of us would prefer most of our cables to
run cooler than that). Paul Cook's "Commentary on IEE Wiring Regs"
states in section 6.1.3, "Ageing of cables": "There is a general
understanding that PVC cables with a continuous conductor operating
temperatue of 70degsC have a life of 20 yers. There is also a rough
guide that for each 8degsC increase in core conductor continuous
operating temperature the life of the cable will be halved". (He goes on
to give a "general formula" for cable ageing, which has the expected
exponential form, but whose numbers don't in fact correspond to a
halving-per-8-degrees... ho hum).

[Pauses to scream blue bloody murder at the idiot dysfunctioncal cat,
which just came into the room and jumped onto the PeeCee. Which has the
new replacement HD for the one which was fading fast resting, unfixed,
atop. Knocks it off. Yes, it's powered up and spinning, and has my "main
personal data" on it. AAAAARRRRRRRRRRGGGGGGGGGGGGGGGHHHHHHHHHHHHH!!!!!!
Time for a fsck/CHKDSK, methinks! And later to fit it securely into the
case, dammit.]

Stefek