In message , Clive
writes

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.
Don't tube trains still carry Short Circuiting Devices (SCDs) anymore?
It used to be that when traction current had been discharged a driver
would clip the device over the outside (live) rail, look away incase of
arcing, then smartly smack the other end down onto the centre negative
rail. It would then be left there in situ for safety until it was
required to restore traction current.

Yes, one at each end of the train with the emergency equipment.
--
Steve Fitzgerald has now left the building.
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