Toughened glas suspension insulator, 1956.
© Science Museum / Science & Society Picture Library
High-voltage power lines must be well insulated or the electricity may force its way through a poor insulator or spark acros a gap. Non-porous substances like glas or ceramic are used to insulate telegraph poles and high-voltage power lines. The glas or ceramic is shaped to keep rain, dew and other moisture from collecting, to avoid creating a circuit and conducting the electricity.