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Dominic · April 20th 04, 04:19 PM posted to uk.railway,uk.transport.london

(Chris Rogers) wrote in message . com...
(Dominic) wrote in message . com...
With an older DC EMU such as a 4-CEP I imagine that the driving motor
car can be uncoupled from the set and run independently under its own
power, and that 2 such cars could form a 2 car train.

This is not always the case with Mk1 EMUs - as I understand it, in
some units (like the 4-CIG IIRC) the driving cars are not the motor
cars - the units have separate driving trailers and a single motor
car. In this case, the 3rd Rail pickup shoes are on the
leading/trailing vehicles and not the motor car itself, so apart from
having no cab, an isolated motor car like this would have no power
supply.

However, in principle, I believe you are correct with some stock which
indeed has driving motor cars.

You're right - I think these units with a central non-driving motor
car started with the 4-CIGs and includes classes 313, 455 and 319.
Equipment on these units appears to be so distributed that I doubt
they can run with less than 4 cars.

Are the driving motor cars of modern DC EMUs such as Networkers,
Junipers, Electrostars and Desiros independent multiple units in this
way? It seems that no set is ever run without a pantograph trailer car
- is this because the motor cars rely on the electronics or other
systems in this car, even when running from the DC 3rd rail? Or can
the motor cars run seperately from the rest of the set?

Modern stock introduces problems through a concept known as
'distributed systems'. The equipment required for the train to work is
not fitted exclusively on the driving or motor cars, but is
distributed along the length of the train. In this case, by removing
one or more cars from the set, some essential equipment would be
removed too.

In the case of Voyagers, you would expect that any formation of 2 or
more cars would be possible as each car has its own engine - in fact
because of distributed systems and other technical limitations, the
minimum consist of a unit is 4 cars.

That's interesting. I didn't know this inflexibility applied to
Voyagers. I thought distributed systems were less common on DMUs.
Maybe it's because of their 3-phase electric transmission?

I was told by a technician that in the case of Class 444/450 Desiros
that it is a very difficult procedure to separate cars in a set
anyway, because they are semi-permanently coupled and not designed to
be separated.

Hope this is of interest,

Chris.

Thanks a lot. Many units have bar couplers within sets, but the number
of cables and hoses connecting Desiro cars is quite incredible.