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Is there a minimum and maximum temperature that a copper wire/s will still work on. Meaning that current will still be able to go through them. Let's say that I have battery that is heated or cooled depending on the environment, and that battery controls a light, that is also heated or cooled, and the wires connecting it are exposed to cold or hot environment. Is there a specific temperature, max / min, that will ensure that current still passes through the wires. I know this might depend on the size of the copper wire, and the specific gauge, but I am considering wires between 18 and 26 AWG. I also figured out that the melting point of cooper is about 1,085 °C, therefore that will in theory be the maximum temperature that a copper wire will be able to operate, I assume. And I am not sure about the minimum temperature.

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  • \$\begingroup\$ Running a wire at a temperature above the kindling point of anything near it is generally considered a bad idea. \$\endgroup\$ – Ignacio Vazquez-Abrams Dec 24 '15 at 3:03
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    \$\begingroup\$ I don't think the ability of copper to carry current is going to be the problem. But hot wires in air tend to oxidize. If you route a bare copper wire through a furnace, even if it is below melting point, it may be destroyed by oxidation in a relatively short time. \$\endgroup\$ – mkeith Dec 24 '15 at 4:18
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    \$\begingroup\$ What is your application, or is this just theoretical? \$\endgroup\$ – gbulmer Dec 24 '15 at 9:45
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    \$\begingroup\$ The wires will be fine until you damage the insulation. The battery, on the other hand, will be very temperature-sensitive. \$\endgroup\$ – pjc50 Dec 24 '15 at 10:27
  • \$\begingroup\$ @gbulmer it is mostly theoretical. \$\endgroup\$ – Viktor Raspberry Dec 24 '15 at 18:07
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The resistance of the wire changes with temperature. There is a given temperature coefficient of resistance for every material. For copper, it is 0.0039/°C. The new effective resistance of the wire is calculated by (deltaR)/(Ro)=(temperature coefficient of resistance)*(deltaT). So, if you know the resistance of the wire at ambient temperature, you can calculate its change in resistance at various temperatures. This will help you decide what size wires you need for a given temperature, or if the temperature is feasible at all.

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  • \$\begingroup\$ you should also add that a copper wire won't suddenly change it's resistance to a very high vale ("non-conductivity") from temperature change alone, as long as you operate it in a reasonable temperature range - maybe don't try to heat it with a blowtorch, and cold won't have much effect except for the change in resistance ThatOneGuy8763 talked about. \$\endgroup\$ – QuantumFlux Dec 24 '15 at 3:35
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0 K to 1358.15 K

-273.15 °C to 1085 °C

-459.67 °F to 1984 °F

You can operate at higher temperatures if you can keep the wire-shaped puddle of molten copper where you need it, but it's usually easier to use platinum wire at that point. (2041 K, 1786 C, 3215 F) and tungsten after you can't use platinum any more (3695 K, 3422 C, 6191 F)

Insulated wires are a bit of a problem at extreme temperatures as insulation tends to melt, burn, or become brittle and crack.

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Wire temperature limits sets first for safety reasons then to ensure circuit operation.

First priority is the insulation protection, not only in the particular cycle of operation (melt etc), but also in long term operation. Insulation degrade each time that the temperature over the specs maximum temperature, shorten their life.

Second is to prevent surrounding materials ignition. Hay for example ignites very easily.

IEC sets as maximum temperature increase the 35 degr Celsius above the environment temperature, which is can taken roughly to around 40 degr. C.

The environment (clima etc, earth/space), the orientation, the encapsulation, the operation cycle (ON/OFF period), the installation place characteristics (in-house, open-air, buried etc) of the conductor plays important role.

As an example in normal operation and for copper magnet wire (formvar coated), the above temperature limit for AWG18 reached when 10A passing the conductor and for AWG26 is 2.8A. However in adiabatic conditions (i.e short-circuit) current reduced to 3.5A for #18 and 0.9A for #26 (bare) suspended on air. In case of coil temperature increase and new calculations should be done.

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  • \$\begingroup\$ And most conductors, when cooled to nearly absolute zero, exhibit superconducting characteristics. That is, they have zero loss and become "ideal" conductors of electricity. Unfortunately, the wire itself and any sort of insulator become very brittle and practically unusable at this temperature. (And keeping it this cold is difficult and expensive, so is only used for things such as the CERN collider.) \$\endgroup\$ – rdtsc Dec 24 '15 at 5:09
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So Copper melts at 1083°C. But that has absolutely nothing to do with Minimum and Maximum temperature for a copper wire to work as a conductor.

Both are determined by the insulation and jacket materials. Insulation breaks down if ambient temperature goes above 100°C. The insulation goes through irreversible chemical changes and starts to burn typically causing fires. Even if you have a jacket which is HOFR (Heat, Oil and Flame Retardant), XLPE and EPR, as insulation, act as wicks for fire and will spread a fire throughout the structure.

It is ultimately why residential wire insulation is colored white. Discoloration means the wire has gotten to hot and the full wire must be replaced. The portion that has burned is no longer an insulator, which means it is becoming a conductor.

Maximum

  • PVC 75°C
  • XLPE/EPR 85°C
  • Silicon 95°C

These maximums are one of the factors which must be taken into account when derating maximum current for a given wire size and insulation material.

Minimum

  • PVC -55°C
  • XLPE -40°C
  • EPR -60°C
  • Silicon –80°C

Insulation becomes brittle below minimum. Not a problem if you are dealing with buildings.

So copper will not melt at 200°C, but it is not much of a conductor if the insulation catches on fire.

Insulation and Jacket Materials

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    \$\begingroup\$ Teflon, fiberglass, ceramic beads (I'm not fond of them but they will do extreme temperatures) and running point to point uninsulated all allow operation at higher temperatures. Ohh, and we have some ceramic fiber stuff I have not personally used that goes to 1205 C listed on the page with this 482C fiberglass yorkwire.com/Fiberglass-900F-482C.html \$\endgroup\$ – Ecnerwal Dec 24 '15 at 4:51
  • \$\begingroup\$ Certainly. Mineral can go to 250C, but I am sure he is referring to AWG for a building. \$\endgroup\$ – StainlessSteelRat Dec 24 '15 at 4:53
  • \$\begingroup\$ I don't know where you are, but in my country not all insulation for building wiring is white. White is used for the neutral conductor and black for the hot conductor. Red is typically used for a third conductor, if needed. Even the outer jacket of NM cable is not always white. For Romex brand, white is used for AWG 14 and yellow for AWG 12, for example. \$\endgroup\$ – The Photon Dec 24 '15 at 17:31

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