Re: The dowel of death

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

Original poster: "B2 by way of Terry Fritz <twftesla-at-qwest-dot-net>" <bensonbd-at-erols-dot-com>

Hi All,
    During the C-17 test the DC power supply usually was at around 85 to 90
kV while charging the 12 stage Marx (1 MV at 50 to 100 kA).  The current
meter would dance around a lot while charging.  I isolated it down to an
insulator support structure.  The structure consisted of a wooden box
structure (4' by 5' high) with a 6" fiberglass L bracket on top for
supporting the HV power supply connections.  A fine conducting path had
been burned through the center of the fiberglass insulator all of the way
down to the wood.  The path then continued along the wood edges all of the
way to the ground.  The total path distance was about 7 1/2 feet!

    After that I would never use wood for any high voltage purpose.  I
found lexan to be a very good high voltage insulator with the additional
advantage that it is transparent.  A piece of 1" lexan rod about 5' long
makes a good low voltage shorting stick.  Fabricate a hook with 1" brass or
copper and bolt it to the end along with copper braid.  The other end of
the copper braid is connected to the high voltage Earth and return ground
at a point where it is visible at all times.  The connection should be
tested with an Ohm meter before every use (Remember the Cockroft Walton
accident?).

Cheers,

B2