On Oct 26, 11:22*pm, (Mark Brader) wrote:

one collector contacting both wires. *Obviously there must have
two separate contacts on that horizontal bar, with insulation
between them.


Also note how high the arm is above the locomotive. *You'd never
fit that thing into a Metropolitan or District tunnel. *They must
have had a different sort of collector in mind.


I've never really looked into the three phase ideas of the Met but I'd
always thought they were looking at the three phase "two wire" system
(i.e. three phases of two conductors and one running rail return) not
with overhead wires but rails, with lower supply voltage than Ganz.
Conductor rails something like the centre and outer rail (like todays
DC) would be the equivalent to Ganz two wires, and the running rails
the return in the same way as Ganz. That way you don't need to expand
tunnels. My interpretation of "not suitable for tunnels" was not
something about not enough wire clearances but one of having all
track rails in a three phase system at a voltage too high for exposed
ground level conductors. Like I said its not something I looked into,
so maybe I misunderstood the whole thing.

If you really wanted to run three phase for the tubes I suggest you
simply use a side contract pickup for all three phases - its complex
at points and crossings but providing one car of the set is in contact
you still have power, and thats no different to a lot of DC section
gaps on todays tube.

--
Nick