On Tue, 13 Apr 2010 10:48:59 -0700 (PDT) someone who may be The
Gardener wrote this:-

Like a lot of things on the railway, its origins are historical. 650 V
was the highest value of "medium" voltage under the old Factories Act,
which meant that (at that time) a permit-to-work system was not
required for "live" work. Such a system of work would these days be
illegal under the Electricity at Work Regs, of course.

That is rather amusing on a railway line equipped with unprotected
conductor rails energised at a nominal 750 V d.c. (For those who
don't know unprotected conductor rails are one of the very few
exemptions under the Electricity At Work Regulations 1989).

The policy for main lines now is that the distribution systems have
either a PSP at each end (WCML practice) or a PSP at one end and an
auxiliary PSP (APSP) at the other (Western practice), to enable
resupply in the event of a failure. In particular, a dual-fed system
will allow a faulted cable section to be isolated and the two sections
to be fed from each end.

Do you know if switching is automatic, remote,or manual? Perhaps the
answer is, it depends:-)

Thanks for taking the time to produce a comprehensive posting. I
found it very interesting.



--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000...#pt3-pb3-l1g54