Asked by: Richard Lindley, Winchester
It’s primarily the effect of the high voltage on the air surrounding the cable. Air is normally a very poor conductor of electricity. But if a sufficiently high voltage is applied across a small distance, electrons from the air molecules are stripped off and start to form a current. This in turn causes intense heating of the air – resulting in crackle and hiss. It’s most common during damp weather, when the air becomes a better electrical conductor.
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