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ampacity explained

What is Ampacity?

Ampacity, also known as the current carrying capacity, 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.

What affects Ampacity?

A handful of factors affect a cable's ampacity, so it’s important to know the specs needed for your application when purchasing a cable. The main factors are:

  • Conductor Size— A larger circular mil area increases current carrying capacity.
  • Insulation— Higher maximum temperature ratings for insulation allow for higher current carrying capacity. It is important to note that the heat generated by the current cannot exceed the maximum temperature rating of the insulation.
  • Ambient Temperature— This refers to the temperature of the environment where is a cable is used. 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 conduits, ducts, trays, or raceways lowers current carrying capacity. However, proper ventilation methods like forced air cooling can mitigate this problem.

Because there are so many variables that can 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.

If you are concerned with a cable’s amperage rating for your next application, one of our experienced representatives can help ensure your product is safe for use.