[time-nuts] Re: Source of small quantities of teflon insulated thermal wires for cavity heating?

[ed breya]

What maximum temperature is needed? That determines the insulation 
material, so if PTFE is already OK for the application, then you can 
conceivably just use light gauge PTFE or Kapton insulated copper wire. 
It depends on the flexibility of your supply equipment or design to 
provide the right current and voltage.

For instance, I have salvaged heating wire from electric blankets over 
the years. In the old days, I think they used a NiCr type wire with 
silicone insulation, while more modern ones look like lots of regular 
thin Cu wire with high temperature PVC insulation. It depends on the 
total length and practical gauge sizes for durability. One I took apart 
recently had about 130 feet of wire, as I recall (which is in the 10-50 
m range mentioned in the OP). These blankets are typically rated around 
100-150 W, 120 V, indicating wire resistance around 1 ohm/ft, and 1 W/ft 
power out. They have temperature limiting fuses built in, so they can't 
melt down if something goes awry.

Another option might be "heat tapes" or such, intended to wrap around 
exposed water pipes for freeze protection. One example I have is only a 
few feet long, and capable of 50 W or so. I don't know what wire and 
insulation types are used, but they are not for very high temperature, 
of course. Try some searching around - there should be all sorts of 
different things for other purposes in lab and industrial work.

Ed