The rated cable temperatures for each (slightly below the actual
melting/charing point), for typical versions are:
The last is the most variable, with different types of glass insulation,
pushing this up to over 700C. You also get glass loaded silicone,
typically rated to about 200C.
Silicone rubber, doesn't melt, it sort of 'chars'. All of these are
You're premise is wrong. Silicone insulation doesn't melt- it chars.
Operating temperature ratings are typically around 200-250°C, IIRC.
Ratings typically run from around 80°C to a bit over 100°C. Burning
moderate quantities PVC can be hazardous.
The immersion heater cable you can buy is, I believe, 180C max
operating temperature, but it's rubber (and I don't think silicone).
I'm not sure these have a 'melting' point, as the rubber is
thermosetting insulation, which will probably jusy go hard, and
eventually char or burn.
There are different types of PVC. The Twin and earth normally
used for wiring is derated to zero current at 70C ambiant, or
designed to operate at 70C at max current (whichever way you
want to look at it). IIRC, this allows for fault currents to
raise the temperature another 90C to 160C (in the time it takes
the protective device to trip), which is regarded as the max
momentary conductor temperature allowed before the cable sustains
instant permanent damage. So I presume it's above 160C but cable
is not designed to operate that hot other than in occasional
Temperature affects the life in years of wiring too. At 70C,
you can expect PVC wiring to last around 23 years, whereas at
40C the life is (calculated) at 1,498 years. See:
Two stories from ages ago... (60s)
My father was OEM sales manager for Pass and Seymour. They used to make
things like big ceramic sockets for street lights. Some of his customers
wanted high temperature pig tail wires on those sockets. For silicon rubber,
the limit was not the insulation. The copper wire (fine strands) inside
corroded too fast at temperatures which were fine for the insulation.
I spent a summer/co-op at GE's Engineering Standards Lab. They
used to test parts coming in from vendors. Standard procedure was
to give a sample part and the spec to a technician. Technician would
read the specs and do all the the tests. My boss told me the story of
a spec that (essintially) called for silicon rubber on flexible
waveguide. Spec said roughly: bake at x C for 1 hour. No problems
sould be visble on the furface of the insulation. x was big.
The technician turned on the oven, cut a couple of lengths of heavy
wire off the spool, bent them into hooks and suspended the sample
(2 ft long?) from the screw holes in the end bells to the rack in
the oven. Then he set the timer for an hour and went to lunch.
A short time later there was smoke all over the place. The solder
holding the end bells on had melted. (I said x was big.)
The silicon rubber had fallen on to the way-hot floor.
Other than a bit of scorching where it had hit the floor, the
insulation was fine.
I thought a side benefit of the cotton covering was that it did not
kink so easily. Mind you, when it does kink then it really does
However I figured from a "side comment" which I read in an electrical
catalogue that the cotton probably had good heat-resistent properties
too. I just don't know how the heat-resistent property might be
If you go back to days of old rubber insulation, cotten was
used on any appliance which got hot, such as toasters, heaters,
etc to help protect the old rubber which would burn. I think
it's only still used on irons nowadays as the solicone
insulation doesn't require any additional heat protection,
but has a rather high friction coefficient with fabrics.