On Thu, 11 Oct 2012 10:12:51 +0100
Steve Fitzgerald ] wrote:
That's an advantage, but the main reason quoted is to do with keeping
the power supplies separated from earth to stop corrosion of cast iron
tunnel segments. The +420 -210 arrangement facilitates monitoring of
the power supplies.

Probably makes the signalling a bit simpler too if there's no return through
the running rails. Any idea how the waterloo & city coped with tunnel
corrosion when it was 3rd rail as I presume its iron segments there too?

B2003