Wire resistance temperature correction calculator

Preliminary estimate

Inputs

Calculation note

Use the result to adjust resistance for voltage-drop review only. Ampacity correction, insulation limits, and terminal ratings still need separate review.

Method

Temperature factor = 1 + alpha x (T - 20 C)

Corrected resistance = base resistance x temperature factor

Resistance change percent = (temperature factor - 1) x 100

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Formula variables

  • Alpha is the selected material temperature coefficient.
  • T is the entered conductor temperature in C.
  • Base resistance is the 20 C resistance value entered by the user.
  • Corrected resistance can be used in separate voltage-drop review.

Assumptions

  • The base resistance is assumed to be at 20 C.
  • Copper uses a rounded temperature coefficient of 0.00393 per C and aluminum uses 0.00403 per C.
  • Temperature-adjusted resistance can change voltage-drop estimates but does not change installation ratings by itself.
  • This calculator does not replace ampacity correction, conductor temperature rating, insulation limits, terminal ratings, or product instructions.

Examples

Copper at 75 C. A 1.000 ohm copper resistance value at 20 C becomes about 1.216 ohm at 75 C.

Aluminum at 40 C. A 0.500 ohm aluminum resistance value at 20 C becomes about 0.540 ohm at 40 C.