In article , 
charles@ellson.demon.co.uk (Charles Ellson) wrote:

> On Thu, 17 Sep 2009 13:21:29 -0700 (PDT), "pippa.moran@gmail.com"
>  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

wrote in message
news:GaydnfYcxtsjOSnXnZ2dnUVZ8sqdnZ2d@giganews.com

>
> 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.

No, Desiros and ElectroStars also come to a complete stop for what seems 
like an age for the voltage change. If anything, it seems like they take 
longer than the 313s, presumably because of the complex electronics and 
computers that may need rebooting.

On Sep 20, 2:10 pm, "Recliner"  wrote:
>  wrote in message
>
> news:GaydnfYcxtsjOSnXnZ2dnUVZ8sqdnZ2d@giganews.com
>
>
>
> > 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.
>
> No, Desiros and ElectroStars also come to a complete stop for what seems
> like an age for the voltage change. If anything, it seems like they take
> longer than the 313s, presumably because of the complex electronics and
> computers that may need rebooting.

The Electrostars can change over on the move, but normally don't. I've
never been on a unit that's done it myself, but know of people who
have. On the West London Line at North Pole Junction, there's little
difference in the time spent stationary between a 313 and a 377,
although the PIS system on a 377 is sometimes still rebooting after
Shepherd's Bush when heading south.

Class 313s can actually change over on the move, very occasionally a
313 will leave Euston on AC and won't stop until arriving at South
Hampstead on DC, I've managed this maneuver at least once during the
rebuild of the Euston station throat.

On Sun, 20 Sep 2009 06:23:35 -0700 (PDT), Andy 
wrote:

>The Electrostars can change over on the move, but normally don't. I've
>never been on a unit that's done it myself, but know of people who
>have. On the West London Line at North Pole Junction, there's little
>difference in the time spent stationary between a 313 and a 377,
>although the PIS system on a 377 is sometimes still rebooting after
>Shepherd's Bush when heading south.

It always struck me as very poor design that the PIS reboots when
changing voltage.  Wouldn't it make more sense for it to operate from
a battery?  Or were the units not designed for changing "on the fly"?

Neil

-- 
Neil Williams
Put my first name before the at to reply.