 As with all electrically powered trains on the former Southern Region, the Class 458 units are powered using third rail at 750 V DC current.Initially, a total of thirty 4-car units were built, with deliveries beginning in 1998, with the full complement in service by 2004.However, they suffered from leaky roofs and failing electronics and were therefore stored from 2004 to late 2005, being replaced by more Class 450 units on the routes they operated.