On Wed, 26 May 2004 16:43:32 +0000 (UTC), TheOneKEA
wrote:


I know little of the history of the Southern Railway, but I believe that
it was decided to let the electrification, parts of which were done back
in the time of Yerkes, to proceed apace - IIRC this electrification
contributed to the sparse tube coverage in South London.

Besides, wasn't 25kVAC thought up well after 700V DC anyway?


This last point is the key to it. The technology to make 25kV
possible, in particular the ability to convert the AC supply to a much
lower voltage DC on board a train, only really became available from
around 1945 onwards. A lot of the former Southern Railway was
electrified much earlier than this. Converting it from 3rd rail to
the overhead system would have been very expensive - almost as
expensive as electrifying it from scratch.

Martin