In article , Aidan Stanger
writes
Do you think it would still be there in 6 years time?
Would the people who would otherwise steal it know whether it was
switched off?

They tend to find out.

With any luck, the changeover could then be done just by setting some
jumpers in a cable cabinet somewhere, rather than having to get the
permanent way gang out again.
I would hope it would be deliberately made a lot harder than that. Do
you really want an accident waiting to happen?
That depends what "an accident waiting to happen" means. How much money
is it worth spending to avoid the combination of two very unlikely
events?

I'd want it to require two separate highly non-trivial actions in
different places (e.g. installing several metres of cable) to energise.
This shouldn't require spending extra money. And, in any case, you'd
need to get the gang out to check all was okay before energising - how
would you know a wire hasn't come lose and is touching another?

I know someone involved in the electrification work on CTRL2. He has to
worry about the fact that the Underground tube tunnels, the King's Cross
station structure, the St.Pancras station structure, and the NLL all
have different values for "earth". He reckons that if he gets things
wrong, opening a breaker at Ashford could cause a lethal change in earth
voltage at the KXSP complex.
Why would a change in earth voltage be lethal?

Because when one "earth" is 90V from another "earth", anyone bridging
the two is going to get a nasty shock.

25000 V AC and 5000 A in complex combinations is hard to get right.

If extending the wires is such a problem, why don't they just extend the
third rail instead?

Because it's even more expensive - you need substations every few km and
there are severe limits on power.

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Clive D.W. Feather | Home:
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