Ampacity is defined as the maximum amount of electrical current a conductor or device can carry before sustaining immediate or progressive deterioration. Also described as current rating or current-carrying capacity, ampacity is the RMS electric current which a device or conductor can continuously carry while remaining within its temperature rating.

The ampacity of a conductor depends on:

  • Its insulation temperature rating;
  • The electrical resistance of the conductor material;
  • Frequency of the current, in the case of alternating current;
  • Ability to dissipate heat, which depends on conductor geometry and its surroundings.
  • Ambient temperature.
As a cable ampacity analysis specialist, Gibson Technologies calculates cable ampacity based on the following standards:


  • IEEE* - IEEE Standard 399 - Recommended Practice for Industrial and Commercial Power Systems Analysis.
  • ICEA* - ICEA P-54-440 - Ampacities of Cables in Open-Top Cable Tray.
  • NEC* - NFPA 70 - National Electrical Code.
  • British Standard** - BS 7671 - Requirements for Electrical Installations.
  • IEC** - IEC 60364-5-52 - Selection and Erection of Electrical Equipment - Wiring Systems.


This cable ampacity analysis program is systematic and simple. For example, for A/G trays, simply enter the tray height, width, and percent fill, the cable ampacity analysis software calculates the derated ampacity based on user specified ambient and conductor operating temperatures.


  • A/G Conduit.
  • A/G Trays.
  • Air Drop – Suspended.
  • Architrave.
  • Brackets.
  • Building Voids.
  • Channel.
  • Cleats.
  • Embedded. Direct.
  • Ladder.
  • Masonry.
  • Open & Clipped.
  • Trenches.
  • Trunking.
  • U/G Direct. Buried.
  • U/G Duct Bank.
  • Window Frame.
  • Wire Mesh.


For duct banks, specify the number of rows, columns, ambient temperature, and soil thermals resistivity, ETAP as a cable ampacity calculation software, computes the derated ampacity based on the hottest location not exceeding the maximum operating temperature.
ETAP Ampacity
Etap Ampacity 2
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