The total Power Dissipated in the cable is dependent on the resistance of the cable, it's length and the square of the RMS current flowing through it.
The power dissipated in the cable is proportional to the square of the current, so if the cable has a cyclic load, the current should be the RMS current rather than the average. If the maximum current flows for a considerable period of time, this must be used as the current to determine the maximum cable temperature, but the power dissipation is based on the square root of the maximum current squared times the period for which it flows plus the lower current squared times the period it flows all divided by the square root of the total time. For example, a cable carries a current of 600 Amps for thirty seconds, then a current of 100 amps for 3000 seconds, then zero current for 3000 seconds. The power dissipation is based on an RMS current of sqrt(600x600x30 + 100x100x3000 + 0 x 3000)/sqrt(30 + 3000 + 3000) = 82.25 Amps.
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