Conductor temperature tool
Conductor Temperature Resistance Calculator
Estimate how copper or aluminum conductor resistance changes with temperature for testing and documentation.
Correct Resistance for Temperature
Enter material, measured resistance, base temperature, and target temperature to estimate corrected resistance.
Result
Corrected resistance
0.6081 ohm
Approximate coefficient: 0.00393 per C.
Result notes. Keep inputs, assumptions, and result together before using this value in project records.
Keep the entered values, assumptions, and result together when adding this calculation to job notes or submittal records. Final installation choices should align with the applicable code edition, equipment listing, manufacturer instructions, local amendments, and AHJ requirements.
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Formula and field context
Estimate how copper or aluminum conductor resistance changes with temperature for testing and documentation.
Formula context
Temperature Correction Chart
The temperature-correction calculator result is a planning checkpoint, not the final conductor approval. Start with a valid ampacity basis, document the ambient-temperature condition, apply the conductor-count adjustment, then compare the adjusted result with the governing equipment termination limit before carrying a usable ampacity into wire size, OCPD, or load documentation.
Formula
Final usable ampacity = min(starting ampacity x ambient factor x conductor-count factor, termination limit).Variables to keep with the result
- Starting ampacity is the calculator lookup value or user-entered ampacity before adjustment.
- Ambient factor is selected from the conductor temperature rating and the ambient condition entered in the calculator.
- Conductor-count factor applies when the current-carrying conductor count requires adjustment.
- Termination limit is the equipment connection rating or marking that can cap the final usable ampacity.
Formula and variables
A simple temperature correction for conductor resistance uses R2 = R1 x [1 + alpha x (T2 - T1)]. R1 is the resistance at the base temperature, R2 is the estimated resistance at the target temperature, alpha is the material temperature coefficient, and temperatures are entered in degrees C. Copper and aluminum both increase resistance as temperature rises.
U.S. field context and example
This calculation is useful when a test record, conductor-resistance check, or voltage-drop note needs to be compared at a different temperature. For example, if a copper conductor measures 0.500 ohm at 20 C, the estimated resistance at 75 C is higher because copper resistance rises with temperature. Keeping the base temperature, target temperature, and material with the result prevents a test value from being compared out of context.
Assumptions and limits
This is a resistance correction, not an ampacity derating factor and not a terminal temperature approval. Actual installations also depend on insulation rating, terminal limits, conductor loading, ambient temperature, raceway conditions, bundling, and adopted code requirements. Use the ampacity and temperature-correction calculators when the task is conductor ampacity or code adjustment rather than resistance comparison.
Common mistakes
Common mistakes include applying a resistance-temperature correction as if it were an ampacity correction, mixing C and F, using the wrong material coefficient, and forgetting that a measured field resistance can include leads, splices, terminations, or parallel paths. Record the measurement setup before comparing corrected values.