"Tom Anderson" wrote in message
.li...
On Sun, 30 Nov 2008, David Hansen wrote:

On Sun, 30 Nov 2008 16:50:43 +0000 someone who may be Steve
Fitzgerald ] wrote this:-

http://www.tubelines.com/whatwedo/tr...guidance/LU_sh
ort_circuiting_device.pdf

Which sadly in this case, the SCD was the cause of the problem.

I guessed that it was one of a series of problems which caused the
voltage from a still energised positive rail to be transferred to the
negative rail. Presumably there was some sort of broken connection or
open circuit breaker/fuse in the feed to the negative rail.

Ah, so although there was no potential between the two power rails, there
was a potential between them and the ground?

Really, you need to connect the two rails to each other and also to the
ground. I was thinking the running rails would make a good ground
substitute here.

Unfortunately, in the incident Steve is referring to, the "ground
substitute" turned out to be a para-medic... (She survived).
--
Cheers, Steve.
Change jealous to sad to reply.