Stefek Zaba wrote in message ...
jim_in_sussex wrote:




...... 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.

was speaking from experience :-(

circuit of mine running a convector fire (not overloaded, at least
theoretically) lasted about 24 months, though I'd be the first to
admit it probably didn't follow the best route to radiate heat & it
was a 30 yer old 7/029 circuit.

It is another example of the unwisdom of running engineering things on
the limit.

Result is that I tend to give priority to keeping cables cool by
limiting prospective loading, eg by using 4mm sq sometimes even if
2.5mmsq would theoretically do.

Incidentally if you do the cost sums on the lower heat loss of 4mmsq
cable v 2.5mmsq cable when running at 30 amps, you find that you save
enough to pay for the difference in cable cost & have less volts drop
at your machines. takes a long time to recover the cost though :-;