On Sun, 30 Nov 2008, Steve Fitzgerald wrote:

In message , Tom Anderson
writes

I recollect an incident a few years ago when the traction current had been
discharged (turned off) due to person under a train. For complicated
reasons, the centre rail had become live at +420v.

This must be some new meaning of the term 'turned off' of which i was not
previously aware! As you say, complicated reasons - but this sounds like
the kind of thing that really, really shouldn't happen. Crumbs.

It had been correctly discharged but been re-fed in error from
elsewhere. You will note that what should normally have been -210v had
now become +420v.

Aha.

Would it be sensible to electrically connect all four rails, with a set of
crocodile clips or something, when working on the track in situations like
this? Then, if there was a mistake which fed voltage to one or more rails,
it would short out, and circuit breakers located wherever the feed-in
was happening would break and cut it off. It would be something you could
do at the site which would absolutely guarantee that there was no
dangerous voltage there. The problem might be the effect it had on other
parts of the system, though.

tom

--
Scheme is simple and elegant *if you're a computer*.