4 ms·

The resistance is not constant and is in fact a function of temperature [0]. Line sag is a proxy measurement for line temperature, since things expand as they h

The resistance is not constant and is in fact a function of temperature [0]. Line sag is a proxy measurement for line temperature, since things expand as they heat up. From [1], most materials have positive alpha coefficients so the resistance increases with temperature. 0. https://en.wikipedia.org/wiki/Electrical_resistivity_and_conuctivity#Temperature_dependence https://en.wikipedia.org/wiki/Electrical_resistivity_and_con... 1. https://www.allaboutcircuits.com/textbook/direct-current/chpt-12/temperature-coefficient-resistance/ https://www.allaboutcircuits.com/textbook/direct-current/chp...

ISL 6y ago
The statement referred to heating driving sagging, which increased resistance. The increase of resistance with temperature is well-known -- I was curious if there is some effect that is directly related to the wire sag (changing morphology, somehow-altered surface area/skin-depth, changing kinks at the connections, some subtlety with increased length (cross-sectional area also increases), etc..).
- Scoundreller 6y ago
  My thought is that after each expansion/contraction cycle, contraction is never exactly back to its previous state. Like bending a piece of metal back and forth, it weakens each time.
- hanniabu 6y ago
  Theoretically I would thing the sag itself should increase resistance since resistance increases with both length and smaller wire diameter. When the line lengthens the diameter should decrease (similar to stretching a piece of gum or putty).
  - leni536 6y ago
    I don't think it should. Heat expansion should slightly increase the diameter.
    - mensetmanusman 6y ago
      Not if the length increases to counteract it.
      - sharpneli 6y ago
        It doesn’t ”counteract” it. All dimensions increase based on the same coefficient. Same percentage increase on all axis. See https://en.m.wikipedia.org/wiki/Thermal_expansion https://en.m.wikipedia.org/wiki/Thermal_expansion and check the coefficient of expansion.
  - function_seven 6y ago
    It's not being stretched by an external force, though. It's expanding due to heat. The diameter would also expand some negligible amount I think.

ISL 6y ago

The statement referred to heating driving sagging, which increased resistance. The increase of resistance with temperature is well-known -- I was curious if there is some effect that is directly related to the wire sag (changing morphology, somehow-altered surface area/skin-depth, changing kinks at the connections, some subtlety with increased length (cross-sectional area also increases), etc..).

Scoundreller 6y ago
My thought is that after each expansion/contraction cycle, contraction is never exactly back to its previous state. Like bending a piece of metal back and forth, it weakens each time.
hanniabu 6y ago
Theoretically I would thing the sag itself should increase resistance since resistance increases with both length and smaller wire diameter. When the line lengthens the diameter should decrease (similar to stretching a piece of gum or putty).
- leni536 6y ago
  I don't think it should. Heat expansion should slightly increase the diameter.
  - mensetmanusman 6y ago
    Not if the length increases to counteract it.
    - sharpneli 6y ago
      It doesn’t ”counteract” it. All dimensions increase based on the same coefficient. Same percentage increase on all axis. See https://en.m.wikipedia.org/wiki/Thermal_expansion https://en.m.wikipedia.org/wiki/Thermal_expansion and check the coefficient of expansion.
- function_seven 6y ago
  It's not being stretched by an external force, though. It's expanding due to heat. The diameter would also expand some negligible amount I think.