Pylons and cables carry electricity through the countryside, but in cities there is no space for pylons and cables. In the city of London there are 29,000km of electrical cable buried underground. If all these cables were put end to end they would stretch to Australia. There are lots of underground substations all over London. These contain many switches and each one controls the electrical supply to specific places and famous monuments.

First broadcast:
15 October 2007

Pupils can design and make model cities with simple circuits and switches to control the lights of their buildings. When learning about materials that are conductors of electricity, children could explain how the switches in these clips can control the electricity travelling to these places and monuments.