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Posted by Paul Coxwell on May 18, 2007, 12:50 pm
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> That is actually not uncommon. Electric supply, whether by overhead
> wire or trackside 3rd rail, has numerous dead spots for a variety of
> reasons. Usually a train is long enough so that one part of it is
> still making contact, or a connector pole is used as Pat described
> below.
> This is commonly done in yards and shops where there is no 3rd rail.
> I wouldn't want to hold such a rod since the power supply -- enough
> to power a heavy train -- is enormous, plus there are nasty arcs.
> But it is done regularly and safely.
The London Underground (subway) system uses both 3rd AND 4th rails,
which makes for many gaps in one or other conductor rail where trains
run over pointwork. The supply is nominally 630V DC, with the 3rd
rail (similar outside position to regular 3rd rail system) running at
about +420V to ground and the 4th rail (centrally mounted between the
running rails) at approx. -210V to ground. The supply is
resistance-earthed rather than being solidly bonded, allowing trains
to continue to run in the presence of a single ground fault.
Movements in service shops and like are made by connecting the DC
supply directly to connectors provided on the trains to avoid having
live conductor rails around.
-Paul
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