Railway electrification in Great Britain began in the late 19th century. A range of voltages has been used, employing both overhead lines and conductor rails. The two most common systems are 25 kV AC using overhead lines, and the 750 V DC third rail system used in Southeast England and on Merseyrail. As of March 2020, 3,758 miles (6,048 km) (38%) of the British rail network was electrified. According to Network Rail, as at 2003, 64% of the electrified network used the 25 kV AC overhead system, and 36% used the 660/750 V DC third-rail system.