RE: Treenails and fires

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Duke, Ronn (CCI-San Diego CCC) by way of Terry Fritz <twftesla-at-uswest-dot-net>" <Ron.Duke-at-cox-dot-com>


Gary,

I seem to recall a month or two ago on the list, a person that was running
his Tesla coil in his apartment, and caught his mattress on fire! He had no
direct strikes to the mattress, but noticed his mattress smoking after a
run. He pulled the it outside and had the fire out before the fire
department showed up. He concluded that the corona on the bed springs from
the coil caused it. The way he described it, Keystone Cops come to mind.

Sparky

	-----Original Message-----
	From:	Tesla list [SMTP:tesla-at-pupman-dot-com]
	Sent:	Monday, April 09, 2001 10:00 PM
	To:	tesla-at-pupman-dot-com
	Subject:	Treenails and fires

	Original poster: "Gary Johnson by way of Terry Fritz
<twftesla-at-uswest-dot-net>" <gjohnson-at-ksu.edu>

	About 30 years ago I was asked by an electric utility to help them
with a
	problem they had been having with fires.  On several occasions, the
large
	wooden poles supporting their 345 kV power lines had caught on fire
at
	conductor level (about 25 feet above the ground).  My conclusion was
that
	the fires started from the point of the nail holding a ground wire
to the
	pole. The point of the nail would go into corona and under just the
right
	conditions of pole age, chemistry, moisture, and wind, would catch
the pole
	on fire. The conductor might drop to the ground and interrupt
service to
	large numbers of customers. My suggested fix was to wrap the ground
wire
	around the pole (just a few turns) rather than run it straight down
the
	pole. The helix would act as a (poor) Faraday cage and would reduce
the
	electric field inside the pole just enough to prevent corona at the
nail
	points. They started installing grounds this way, and to my
knowledge, never
	had another fire.

	The concern is that most of us operate Tesla coils at or above 345
kV fairly
	close to walls and ceilings containing nails driven into wood. I
would
	expect some of these points to be at least close to corona.
Apparently, we
	get away with the practice because the wood is drier than a power
pole and
	because we do not operate 24/7. Still, it seems wise to have
adequate fire
	insurance on our test facilities. I know the Richard Hulls among us
	regularly set our labs on fire with direct streamer strikes, but I
wonder if
	anyone has experienced a fire that occurred later, in a situation
where a
	direct strike would not appear to be a factor?

	Gary Johnson