This is a photograph of a "pedestal insulator," a 3 metre column of insulating bitumen, supporting a potential difference of 300,000 volts. Several of these have exploded when relatively small amounts of rain-water have seeped into them at electricity sub-stations. The conducting water drops are stretched by the electrical stresses to form long, thin conducting paths.

(Photograph taken at National Grid laboratories, Leatherhead)

This problem was studied by Neville Dubash, my PhD student.

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