Hi, What is your explanation for

[zub]

Hi,

What is your explanation for this paradox? (at least for me!)

1. The insulation resistance decreases if the heat is increased.

2. The current carrying capacity decreases if the heat is increased. (it means the conductivity decreases so the resistance increases...)

it seems a paradox, isn't it.

thanks in advance.

zub.

 

[electricpete]

I'll offer a comment, not an explanation.

An equivalent statement is that conductors tend to have a positive temperature coefficient of resistance and insulators tend to have a negative temperature coefficient of [inuslation] resistance.

I don't know the physical reasons why it is so.

 

[TheBlacksmith]

Electrical resistance, in my mind, may be explained by elastic collisions between the electrons and the atoms. As the conductor temperature increases, the atoms move more (more internal energy), increasing the probability of collisions and therefore the resistance. I'm less sure of the insulation decrease, except generally ionization of substances is easier at higher temperature; possibly this explains it.


Blacksmith

 

[peterb]

Another comment on point 2 would be that the current carrying capacity of a conductor is related to the maximum operating temperature of the conductor, rather than the resistance.
The upper limit of the operating temperature is set by the annealing point of the conductor metal, or by the temperature at which any insulating material will be damaged. Note that conservative values will be specified for the current, to allow an adequate safety factor.

 

[maximka]

The resistance of a conductor increases with the temperature rise due to higher athom vibration and other related internal kinetic processes, such as enthropy rise. The resistance of an insulator decreases because the energy of the electrons is increased with the temperature, and therefore it is easier for them to become free and start flowing when external field (voltage) is applied.