Allied Encyclopedia – Current Carrying Capacity of Copper Conductors

Allied EncyclopediaCurrent carrying capacity, also known as ampacity, is defined as the maximum amperage that can flow through an insulated wire or cable before reaching a temperature high enough to melt the insulation or the conductor.

Amperage refers to the strength of the current in its unit of measure, the ampere. One ampere is the current that one volt of electricity can send through one ohm of resistance.

The amount of current a wire can carry is determined by several factors, including:

  • Conductor Size – Larger circular mil area increases current carrying capacity.
  • Insulation – Higher maximum temperature ratings for insulation allow for higher current carrying capacity. Heat generated by the current can not exceed the maximum temperature rating of the insulation.
  • Ambient Temperature – Higher surrounding temperatures lower current carrying capacity. Less heat can be produced by the current before reaching the maximum temperature rating of the insulation.
  • Conductor Number – Increased numbers of individually insulated conductors bundled together decrease heat dissipation, lowering current carrying capacity.
  • Installation Conditions – Restricted heat dissipation faced by conductors installed in conduit, duct, trays, or raceways lowers current carrying capacity. However, proper ventilation methods like forced air cooling can mitigate this problem.

Because so many variables affect current carrying capacity, no chart can be developed to account for all limiting factors in the design of systems in which amperage ratings are critical.

About awcwire
Allied Wire & Cable is a value-added manufacturer and distributor of electrical wire and cable, tubing, and more. We are a family owned and operated company, serving a wide range of industries, including the military, automotive, aerospace, and telecommunications markets. Allied is headquartered in Collegeville, PA. Additional locations can be found across the US, in Phoenix, AZ; Bedford, NH; Pewaukee, WI; Rochester, NY, Tampa, FL; and Mt. Juliet, TN. For more information on Allied, visit our main website at

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