On Mon, 24 Nov 2008 20:32:20 -0000 someone who may be
wrote this:-

Is a fourth rail really necessary out that way, however? I always understood
that they were really needed only for the tub sections of the tube, to help
power flow into the motors. I heard this on the Island Line, where 38 stock
operates only with a 3rd rail.

It operates there after being modified to allow the traction supply
to travel via the running rails. Heavy electric currents through
bearings is not a good combination, hence the modification.



--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54