Cable ratings are based on the resistance of the cable, the surface area of the cable, and the temperature rating of the insulating material. The rating applied to a cable is at a given ambient temperature. Variation in ambient temperature will result in a variation of the cable rating.
The resistance of the cable is a function of the material from which the conductor is manufactured, i.e. copper or aluminium, and the cross sectional area of the conductor.
The Cable size can be nominated in either square millimeters, or in the US American Wire Gauge. The European metric ratings are based on figures from VDE 0100 and the American Wire Gauge figures are taken from the National Electrical Code. (NEC)
Ambient Temperature. The air temperature around the cable.
Ventilation. Free air movement around the cable will allow more cooling than cables enclosed in conduit or trunking.
To calculate the current rating of a cable, select the cable size and the ambient temperature around the cable in degrees Celsius or Fahrenheit and the ventilation. ("In Free Air" or "Enclosed" in conduit or trunking.) The current rating of a copper cable is displayed.
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