Wiring and Protection
Conductor Temperature Derating Calculator
This calculator evaluates derated ampacity for a single wiring and protection scenario. It uses base ampacity and temperature factor and shows the equation behind the displayed value.
Enter values for Derated ampacity
Check the source and units before calculating.
Measurements and entries
Record ambient temperature, bundling, insulation class, and termination conditions. If operating conditions changed between readings, calculate separate cases.
Check every prefix before entry; micro, milli, kilo, and mega are not interchangeable. Another relevant worksheet is BJT Bias Calculator.
- Base ampacity
- Default example: 40 A. Enter base ampacity in A.
- Temperature factor
- Default example: 0.87. Enter temperature factor.
Formula used on this page
The displayed result follows ampacity = base × factor. The entered quantities are Base ampacity and Temperature factor.
The defaults produce 34.80 A. Replace them with measurements from one operating state.
Calculate derated ampacity from base ampacity and temperature factor. For the companion bundled ampacity calculation, open Bundled Cable Derating Calculator.
Changing Base ampacity
Change Base ampacity from 40 A to 48 A and preserve the rest of the case. This moves the answer from 34.80 A to 41.76 A.
This isolates one variable; a real system may change several at once.
What the number means
Use Derated ampacity as one quantified check within the larger decision. Compare it with ampacity, voltage-drop, fault-current, and protection limits.
Label alternate cases rather than overwriting the baseline.
Assumptions and limitations
Use a factor for the actual insulation and ambient range.
Outside the entered variables, consider termination heating, installation method, ambient temperature, and grouping. Do not hide omitted behavior inside an unexplained correction factor.
Use the installed route length, conductor material, and actual current path.
Common questions before using the result
Can an input legitimately be zero?
Use zero only when it describes the physical condition. It is not a substitute for missing data.
What data should go into Conductor Temperature Derating?
Choose entries that describe the same case. Record ambient temperature, bundling, insulation class, and termination conditions.
Where is this derated ampacity estimate simplified?
Use a factor for the actual insulation and ambient range. A broader review should include fault duration, protective-device curves, and conductor thermal limits.
What explains a gap between calculated and observed derated ampacity?
Recheck units and operating state before investigating fault duration, protective-device curves, and conductor thermal limits.
What should remain fixed in an alternate case?
Keep unaffected entries fixed so the cause of the difference remains visible. Keep one-way and round-trip lengths clearly identified.
Does Conductor Temperature Derating Calculator choose a final rating?
The calculator does not approve equipment or supply an unexplained margin. Compare against the selected conductor and protective-device ratings.