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[email protected] · September 19th 09, 09:30 AM posted to uk.transport.london

In article ,
(Charles Ellson) wrote:

On Thu, 17 Sep 2009 13:21:29 -0700 (PDT), "
wrote:

MIG wrote:
On 17 Sep, 10:15, "Peter Masson" wrote:
"Sim" wrote

Some differences between Overground and Underground:
1. Third rail electrification rather than fourth, so not
compatible for through running.

The NLL is 25 kV OHLE between Acton and Camden Road, and between
Dalston Kingsland and Stratford, and will be all the way between
Acton and Stratford once the NLL refurbishment is complete. The
WLL switches from 25 kV OHLE to 3rd rail between North Pole
Junction and Shepherds Bush. Goblin remains diesel worked (and
if it is electrified it will be 25 kV OHLE.

One small question - does newer dual voltage stock (since the 313s) have
the capability to switch between third rail and overhead on the fly
between North Pole and Shepherd's Bush? The 313s were designed only to
switch in stations (Drayton Park actually) but no-one envisaged a
changeover point between stations in the 1970s.

BTW, the Broad Street to Dalston line, most of which is being
incorporated into the ELL, was originally 4th rail, but IIRC was
converted to 3rd rail before closure.

That's my recollection too.

And all electrified parts of the current London Overground were four
rail at some point, weren't they? Ah, maybe not Dalston to
Stratford.

I believe the stretch from Queens Park to Harrow & Wealdstone is still
four rail, otherwise Bakerloo passengers would have to get out and
push!

It is 3rd rail with the 4th rail bonded to the running rail which
carries the traction return current. The LU 4-rail system does not
have a deliberate electrical connection between the 3rd/4th rails and
the running rails and is only loosely connected to earth/0v to enable
control equipment to detect earthing of either electric rail. A
further consequence of this arrangement is that trains running over
such sections require higher-rated insulation than is necessarily on
LU (660v to earth rather than 420v to earth) although IMU all current
LU stock has been so equipped since the 1960s

You are overlooking East Putney or Putney Bridge to Wimbledon which has
had earth bonded current rails since the first world war. Also Gunnersbury
to Richmond and probably East of Barking or thereabouts until 50 years ago.

--
Colin Rosenstiel