The solution adopted was electrical power, provided via a third rail (This is now a fourth rail) beneath the train, but offset to the west of centre for clearance reasons. Although the use of electricity to power trains had been experimented with during the previous decade, and small-scale operations had been implemented, the C&SLR was the first major railway in the world to adopt it as a means of motive power. The system operated using electric locomotives built by Mather & Platt collecting a voltage of 500 volts (actually +500 volts in the northbound tunnel and −500 volts in the southbound) from the third rail and pulling several carriages. A depot and generating station were constructed at Stockwell. Owing to the limited capacity of the generators, the stations were originally illuminated by gas. The depot was on the surface, and trains requiring maintenance were initially hauled up via a ramp although, following a runaway accident, a lift was soon installed. In practice, most rolling stock and locomotives went to the surface only for major maintenance.