"GB" threefiddy.com> wrote in message
news:00bab05d$0$20306$c3e8da3@news.astraweb.com...

It's to persuade a potential lightning strike that "we are a gooood keeeed"
and we are actually on the ground so don't bother us and go for something
else that's sticking up :-) Similar to the 'lightning arresters' used on
house chimneys etc. That overhead conductor is earthed at every
pole/tower. I suppose it's a bit like a Faraday cage. Ergon (all of Qld
except the SE corner) uses an aerial earth over sensitive conductors, eg
near reclosers and zone substations. The explanation may be a bit suss as
I'm a mech/civil rather than elec engineer, but it'll give you the basic
idea :-)

Along those lines, many years ago I was mixed up in a fatigue study of
copper conductors used on SWER* lines. Inspected and labelled the
conductor at the pole tops along the Stonehenge (near Longreach) SWER by
cherry picker before the line was dropped and the conductor sections
returned to the Uni for testing. At one place there were 3 burnt poles on
the ground beside the upright one - 3 lightning strikes on the same
location! The 'linies' said that was not unusual......

*SWER = single wire earth return. A high voltage reticulation system used
in rural areas where just one conductor is used - the ground forms the other
one.

Ok - it's off charter and off topic - sue me :-)