EMI filter hookup

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

Original poster: "Lau, Gary by way of Terry Fritz <twftesla-at-uswest-dot-net>" <Gary.Lau-at-compaq-dot-com>

Last week I changed several components on my coil which required that I
experimentally retune it.  I was perhaps 1-2 minutes into this tuning when
performance suddenly diminished, the circuit breaker tripped, and a burning
smell filled the garage.  It turns out that my 30 Amp Corcom EMI filter had
toasted.  I had been using this filter for well over a year with no problems
and I'm sure that my 15/60 NST was not pulling more than 20 Amps.

I examined the hookup and came to the conclusion that one or more of the
filter's internal caps had been over-volted by the hookup configuration.  I
had connected the filter "backwards" as is frequently suggested, with the
LINE side connected to the NST primary.  The 3rd wire ground from the wall
is not used anywhere in the coil beyond the variac so I was connecting the
RF ground to the filter's case instead.

I now believe that in a configuration where the filter is located at the NST
where no 3rd wire ground is available, that the "backwards" configuration is
inadvisable and was responsible for the failure of my filter.

I've added a page to my web site with schematics illustrating the good and
bad ways to hook up the filter.  I don't know if I'm the only person who ran
in that backwards configuration with the RF ground, but hopefully I can save
someone else's filter from toasting.

Oh yes, it also appears that in addition to being self-destructive, that bad
configuration also made the EMI fed into the household wiring worse than if
no filter was used at all!

The new page is at: http://people.ne.mediaone-dot-net/lau/tesla/emifilter.htm

Regards, Gary Lau
Waltham, MA USA