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.
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.
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.
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.
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.
- 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.
- 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.