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RE: Counterpoise and MMC demise



Original poster: "Peter Lawrence by way of Terry Fritz <teslalist-at-qwest-dot-net>" <Peter.Lawrence-at-Sun.COM>

Chris,
       your 6kV-30mA NST has a Res Cap value of 13.26-nF, and your cap is
(22 / 6) * 4 = 14.67-nF which is too close for a static gap - the Res
Cap value is the value at which the NST-Cap combination can resonate up
to absurdly high voltages.  Static gaps are notorious, if the gap for
whatever reason fail to fire once the voltage on the cap doubles, if it
fails to fire for twice in a row the voltage on the cap triples.  You
were probably just "lucky" that your cap did not fail while running with
the earth ground, switching to a counterpoise probably had nothing to do
with it.  My first recommendation is to use about 1.5 * the NST Res Cap
value for your primary cap when using a static gap, add at least one and
maybe two strings to your cap.  My second recommendation is to use
caps that have already been tested in TC service, I'm using the panasonic
ones that I got though Terry and have never had one fail.  Lastly, I'm
I'm using longer strings and only putting 750VAC per cap, even though
Terry and others report long life using the DC rating in TC-AC service.

good luck,
-Pete.

(ps, the Res formula for 60-Hz NSTs is nF = 2.652 * mA / kV).