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May 21st 04, 06:08 AM

(WShoots1) wrote in
:

Rain usually washes off the dust that collects on insulators and causes
arcing during foggy or humid weather. But if a carbon path has developed
on an insulator, rain will worsen the problem.

Bill, K5BY

Everyone assumes the insulators prevent line voltage from escaping and
going to ground. Actually on an AC power line due to the construction of
the insualtors, something very different happens. Typical construction has
the power wires passing over the insulating material, which is mounted on
a metal pin or post. The wire is held in place with a pigtail that passes
through the insulator and is wrapped on the power line conductor similar
to the construction of a 450 ohm ladder line. This gives you a poer wire
that is mouted on a non conductive material with a conductor on the
opposite side of it. That gives you a capacitor and the power line has AC
on it. So the power line voltage is coupled to the top of the pole. Under
normal conditions the very hig resistance of the wood in the pole prevents
significant current flow. However this changes if the top of the pole is
rotten and more current begins to flow. A wet and rainy day will make
conditions worse and increase leakage current flow. Tha's why you have to
be very careful working in the communications space (telephone//cable tv)
further down the pole. As the pole deteriorates, this condition get worse
and worse and the current increases to the point where the pole top heats
up and starts to burn. Thats why pole fires usually occur on wet days and
usually near the top of the pole.

--
Panzer