What is ampacity?

This is a term for the maximum current carrying capacity, in amps, of a particular device. The current carrying capacity is normally associated with electrical cable and is determined as the maximum amount of current a cable can withstand before it heats beyond the maximum operating temperature. The effect of resistance to current flow is heating and this is dependent upon the size of the conductor, the insulation material around the conductor, and the installation environment.The larger the conductor size the lower the resistance to current flow, meaning less heat associated with this resistance. Increasing the conductor size increases the current carrying capacity. Similarly,  the higher the temperature resistance of the insulating material, the higher the ampacity or current carrying capacity. A 90°C rated insulation will have a higher current carrying capacity than a 70°C rated insulation.

The installation environment and the temperature of this environment affects the ability to dissipate heat away from the cable and so also affects the current carrying capacity. Cable used in air or ground at lower temperature will have a higher current carrying capacity than cable in air or soil at higher ambient temperatures.

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