Eurostar train and a commuter train. The Eurostar train (right) is running on the Channel Tunnel Rail Link between London and the Channel Tunnel in the UK. It is powered by overhead wires or catenary structures, which supply electricity. The commuter train (left) is running on a line from London to Ashford, which uses the older method of a third live rail to supply electricity. The third live rail method can supply up to 1200 volts. It is more compact than overhead wires and is used in narrow tunnels, however it is vulnerable to snow and icy weather conditions. Overhead wires require alternating current (AC) and will supply up to 25,000 volts.