On 08 Apr 2008 21:13:49 GMT someone who may be Matthew Geier
wrote this:-

Any one working on a high power system will want the assurance some
idiot can't turn it back on and kill them, hence the highly visible short
to earth bars/wires. If some one tries to turn it back on, the short to
earth should be a sufficiently good 'fault' to trip it off again saving
your own skin from such stupidity.

That rather depends on the system. For example it is difficult to
apply an earthing wire to a cable one is about to open up to joint,
but one is a sensible precaution on a bare conductor.

Where the system covers a relatively small area then the obvious way
to manage things is to use locks. If people are doing the same sort
of work over a small area then they can have their own lock which
they keep the key to. An example would be a workshop where several
people work on the electrical parts of a train.

If there is a larger system with someone responsible for the whole
system then the way to manage it is to use locks, the keys for which
are locked into a box. This box has a key for those doing the work
and a key for the person responsible for the system.

Such systems become unmanageable over large areas with remotely
operated switchgear.



--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54