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.

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