↑Per 'Secrets of the Underground' Series 2 Episode 2. The change in electrification was part of the modernisation by Network Rail in the mid 1980's. Network Rail opted for their standard of 750 volts for DC lines (though they actually converted the W&C to four rail to solve problems with earth currents in the cast iron tunnels). The W&C consequently has its own electrical sub station located in the depot at Waterloo. The line was subsequently transferred to London Underground in 1994. Consequently the Waterloo and City is the only deep level tube railway operating at 750 volts (all other lines being 630 volts).