In article , Acrosticus
writes
From: Matthew Malthouse
Date: 06/08/2003 20:13 GMT Daylight Time
Anyway, anyone know the nature of the damage? Overheads stretching in
the heat? Or something more esoteric?
Well, not too esoteric. The wire expands and contracts like everything else
acccording to temperature, but it needs a certain amount of tension as well so
that pantographs don't get round the wrong side of it and bring the lot down.
On occasional OHLEs you'll see an assembly with removable weights that are
connected to the overhead to tension it. These weights are slotted onto a bar
and plate arrangement. If you can't get enough weights on the bar to remove the
sag (and, after all the bar has a finite length so it'll happen some time)
you're not tensioning the wire enough so it will sag, probably bounce as trains
pass underneath and could allow the panto to "wrong side" it thus pulling the
lot down.
IIRC the OLE out of Liverpool Street is pre tensioned and does not have
the weights you mention to re tension it when it stretches. I think once
one gets past about Gidea Park there is tensioning.
--
John Alexander,
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