Ampacity Derating Calculator

Inputs

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Ampacity from the adopted table and conductor insulation column before correction or adjustment.
A
Maximum ampacity allowed by the termination/equipment temperature rating. Enter the same value as base ampacity when there is no separate cap.
A
Actual expected load current before the load multiplier.
A
Use 100% for non-continuous screening or a higher multiplier when your design method requires it.
%
Correction factor for ambient temperature from the adopted code or manufacturer data.
Adjustment factor for current-carrying conductors in the same raceway, cable or bundle.
Optional extra multiplier for rooftop adders, cable tray, manufacturer data, local rules or project-specific derating. Use 1.00 when none applies.

Results

Default result
Edit inputs
Usable ampacity(I_use)
100A
Pass

derated conductor ampacity controls

Also computed

Design load current(I_design)Pass100A

125% of entered load current

Ampacity margin(I_margin)Pass0A

Usable ampacity meets the design load.

Utilization(U)Pass100%

Adjusted ampacity before cap(I_adj)100A

Terminal-limited ampacity(I_term_lim)100A

Combined derating factor(F_total)1

Method notes 3 notes
  • Adjusted ampacity = base ampacity x ambient correction x conductor-count adjustment x other derating factor.
  • Usable ampacity is the smaller of the adjusted conductor ampacity and the entered terminal/equipment cap.
  • This does not choose a conductor size or code-compliant overcurrent device. Use the adopted code edition, listed equipment instructions and qualified review for final work.

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