Electrical Cables Ampacity

Cable ampacity or current carrying capacity is the maximum current that the cable can carry continuously at maximum operating temperature.

Current passing through a cable faces electrical resistance and produces heat. The temperature of the conductor rises depending on the current value. Here comes the cable ampacity.

What determines conductor ampacity?

Cable current depends mainly on how much temperature it can handle without failure! The maximum temperature is affected by many factors, like cable laying method, soil thermal resistivity, laying depth underground, and other factors that affect the current carrying capacity of the cable, Other factors are listed below:

  • Conductor material.
  • Insulation around the cable. i.e. XLPE or PVC, XLPE insulated cables can carry more current than PVC insulated ones.
  • Laying method of the cable. i.e. in the air, underground, or in the duct.
  • Laying in Trefoil or flat formation.
  • The ambient temperature.
  • Soil thermal resistivity.
  • Burial depth underground.
  • Duct inner diameter for cables in the duct.
  • Number of cables in the same laying path.

Some of the above factors are fixed like cable material and insulation, while others can vary from one application to another like ambient temperature. Cables are manufactured for specific working conditions, if the working conditions are not the same as the designed ones, we apply correction for cable ampacity. The correction factors are known as derating factors.

I have written a detailed article about cable correction factors, Read it for more information here.

Where to find Cable ampacity Tables?

Each cable manufacturer has a product catalog. This catalog contains data and tables of the cable’s electrical and physical properties.

Voltage drop, Derating factors, short circuits, table of ampacity, and more electrical data are in these tables.

One of the most important tables that everyone who works with cables needs it regularly is the ampacity or current carrying capacity table.

In the table, we find the cable cross-section area and in the first column the resistance and current that each cable size can carry. There are three current values for each cable size because this current value is affected by the laying method and other correction factors.

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