In article , Matthew
Geier scribeth thus
On Tue, 08 Apr 2008 09:52:47 +0100, tony sayer wrote:


yes I remember that too, presumably 4 parallel sets of 3 lamps in series
so the -240/+410 gives each lamp about 250V?

I thought an 'eff off size shorting bar was the best insurance;!...

You don't drop a shorting bar across a live supply. The effect would be
some what spectacular and will probably throw molten metal around,
possibly causing nasty injuries.
People have been injured in the power industry by closing earthing
switches onto a live supply and then being splattered with molten metal
when the earth switch vaporised. (As they are not designed to switch live
and take the full fault current across their closing contacts)

You don't short the circuit till you have tested it's actually dead.
Then short it so that if some one accidentally turns it back on while you
are working on it, the short circuit causes it to trip off again. And you
make short your short is securely attached so that in the event is really
does get energised, the sudden large current flow doesn't cause the
shorting wire/bar to fly off and disconnect itself, thus allowing the
circuit to be fully energized and then fry you.



Ever heard of SIDE?.

Switch off
Isolate
Dump
Earth

One wouldn't recommend for a moment chucking an earthing bar or cables
across a live line!.

A shorting/earthing system should be suitable for the currents involved.

There will be a difference for linesmen working on an 11 kV overhead to
someone on an LU line!...



--
Tony Sayer