The British Rail Class 506 was a 3 carriage electric multiple unit (EMU) built for local services between Manchester, Glossop and Hadfield on the Woodhead Line, which was electrified in 1954 on the 1,500 V DC overhead system. Design There were eight three-car units, ordered in 1938 by the LNER and built in 1950, but they did not enter service until June 1954. Similar in design to the Class 306 EMUs (prior to their conversion to operation), and built on the same production lines (making a total of 100 units of basically similar design), they were equipped with air-operated sliding doors. Formation Each unit was formed of a Driving Motor Brake Third (seating 52); a Trailer Composite (seating 24 first class and 38 third class passengers); and a Driving Trailer Third (seating 60). Third class was redesignated Second across the whole of BR on 3 June 1956, while the first class seating of these units was declassified to second in early 1960. The eight 3-car sets were formed into 6-car trains at peak hours. The frequency of the Glossop/Hadfield service at peak times was every 30 minutes, and the round trip took nearly 90 minutes, requiring six of the eight units in service each weekday. With one spare unit, and one away for works overhaul at a time, there was no scope to use the units for other tasks. Electrical equipment The EMUs were equipped with a single diamond-shaped pantograph, mounted over the driver's cab and adjacent guard's compartment at the outer end of the driving motor carriage. This gave a ready identification feature because, following the withdrawal of the Manchester-Altrincham units in May 1971, all other overhead-line EMUs operating in the Manchester area had the motor coach, and thus the pantograph, in the middle of the unit. Unlike the similar Class 306, the eight Class 506 units remained solely equipped for 1,500 V DC operation for their entire lives. This made them unable to operate on any lines away from the Woodhead route when other lines changed to AC operation. They rarely operated east of Hadfield anyway, due to low gearing and the risk of overheating; however, trials were conducted in 1969 to assess the possibility of use through the Woodhead Tunnel. Motors Each power car had four 185 hp GEC traction motors, giving a total of 740 hp per 3-car set. Numbering British Railways numbers were: Motor Open