Bulleid/Raworth Co-Co Electric Locomotives (Class 70)

By the late 1930s the Southern Railway's electrified system had expanded beyond the suburbs sufficiently to consider using electrical traction on more than just multiple units. Accordingly two experimental Co-Co mixed traffic electric locomotives were designed and constructed, these being a co-operation between Oliver Bulleid (Chief Mechanical Engineer - responsible for external design, mechanical parts and maintenance) and Alfred Raworth (Chief Electrical Engineer - responsible for the electrical systems). However a fundamental problem with third rail pick up locomotives had first to be solved. Since the distance between the outer pickups of any such loco - even long ones as these turned out to be - is much shorter than on multiple units the traction supply could be lost when the gap between conductor rails is longer than the distance between the locomotive's pickups . This situation is commonly referred to as "gapping". This was solved by instead of the traction supply being used, via control systems, to power the traction motors directly it was instead applied to drive two motor generator sets with heavy flywheels. Thus power to the traction motors would be maintained by the M-G sets being driven by the flywheel when the traction supply was briefly lost. These motor-generator-flywheel sets were referred to as "boosters" which also became the nickname for the class. These locomotives were also fitted with a pantograph for overhead pickup in sidings and depots where a conductor rail presented danger to staff.
Side elevation plan from Southern Railway publication, May 1944.
These locomotives were very solidly constructed with solebars and main frames welded up from channel sections carrying a boxy body made of metal sheets fitted over a frame. They were 56ft 9in long, weighed 99 tons and had a tractive effort of 40000lb. There were cabs at both ends and their design was similar to contemporary EMUs (such as the early "Sheba" Subs) with a domed roof. Between the cabs there was the electrical compartment which also included an electrically heated boiler for carriage heating, however this was partitioned off to prevent water and steam ingress to the electrical equipment. The electrical systems and ancillary units were supplied by the English Electric Company and sub contractors. The plate frame bogies were of riveted and welded construction with five sandboxes per side and had BFB wheels of 3ft 6in diameter.
CC1 Co-Co NºCC1 in photographic grey and under the wires in Balcombe sidings on an unknown snowy date sometime in 1941 or 2.

photograph reproduced from Southern Railway publication.

NºCC1 at Balcombe once more, note that the planking between the rails in the above photograph is absent here. The "speed whiskers" disappeared with a repaint in 1942.

photograph reproduced from Southern Railway publication.

CC2 Co-Co NºCC2 with new lettering and painted blue, pictured during 1948 working a Chichester to Norwood goods train.

photograph by H M Madgwick and reproduced from the July/August 1948 issue, with the kind permission of the Railway Magazine

The first locomotive numbered CC1 (renumbered to 20001 by BR) emerged from Ashford works in 1941. Until 1942 it ran in photographic grey livery with three horizontal lining stripes, two on the body sides, one on the lower part of the roof, which were extended round the cab front, rounded down and brought to a point which in later years would be known as "speed whiskers". This was replaced by malachite green livery with "Sunshine" Southern lettering and yellow lines at solebar and cantrail level. The second locomotive CC2 (20002) emerged from Ashford in 1945 in malachite green livery. These two were used on express passenger and goods trains and with the benefit of experience were modified to improve their efficiency.

20002 at Three Bridges in the days before the headcode panel was fitted, and well before the advent of yellow ends!

photograph by Keith Harwood

All photographs are copyright

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This page was last updated 14 January 2009

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