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I am currently experimenting with resistance wire to generate heat. I have 2 types here. One is insulated, the other isn't. The one that isn't insulated works just fine, but the insulated one gives a huge amount of smoke the first time I heat it and then the outside becomes completely black. After that the smoking stops.

What is the use of that insulation if as soon as I put some current on the wire it smokes and turns black?

I measured the temperatures and I did not exceed 80 degrees Celcius. Voltage applied is around 10V and it draws a current of 2.5A.

Some info about the wire: Resistance: 10 Ohm / metre Diameter: 0.25mm Material: CuNi44

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    \$\begingroup\$ Sometimes you want things to be insulated...so that they don't short to other things. \$\endgroup\$ – Bort Feb 13 '18 at 21:47
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    \$\begingroup\$ I do not believe that the insulation turned completely black at 80C. How did you measure the temperature? \$\endgroup\$ – mkeith Feb 13 '18 at 21:50
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    \$\begingroup\$ the insulated wire is probably meant for lower current application \$\endgroup\$ – jsotola Feb 13 '18 at 21:50
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    \$\begingroup\$ I'm with @mkeith- no way did that happen at 80°C. More likely hundreds of degrees C. It really is not trivial to accurately measure the temperature of a thin wire. \$\endgroup\$ – Spehro Pefhany Feb 13 '18 at 22:03
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    \$\begingroup\$ Take a small sample of the insulated wire and put it in a pot of boiling water. If 80C is really enough to roast it, then it should turn black and smoke when you remove it from the water. \$\endgroup\$ – mkeith Feb 14 '18 at 3:00
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Resistance wire is used to make heaters (usually alloys such as Nichrome or Kanthal). This type of wire is refractory (has a high melting point) and is usually resistant to oxidation so you can get it very hot in air without undue shortening of the life. Sometimes it is shoved into a fiberglass braid or ceramic braid but usually the wire maker supplies it bare.

Resistance wire is also use to make wirewound resistors (typically different alloys such as Manganin or Constantan). It is typically insulated. Such wires are not intended to get very hot- the advantages of the alloys used are that they have a low TCR (Temperature Coefficient of Resistance) near room temperature up to perhaps 100°C). The insulation may be an enamel of some kind, polyester or some similar thermoset or thermoplastic, depending on the intended application.

The two classes of alloys are quite different and the latter probably won't make a very good heater and the former won't make a very good resistor.

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Insulated resistance wire is intended for low temperature applications... like keeping a pipe from freezing by heating it to say 10C. You need the insulation since wrapping a bare wire around a metal pipe doesn't work too well.

There are some higher temperature insulations though that will let you go higher, but not for red hot wire. (Not that that link is heater wire).

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