RE: 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>

My EMI filter was located at the NST, rather than at the variac.  I have a
3-wire cord running from the variac to my coil assembly:  neutral, variac
out (hot) for the NST, and 120V (hot) for the gap motor.  Since nothing else
at the coil assembly connects to 3rd wire ground, and since all 3 conductors
of the cable are spoken for, and since 4-conductor 14AWG cable is uncommon,
that's why my EMI filter didn't connect to the 3rd wire ground.

It appears that it would have been better to have located the EMI filter at
the variac so that I could have used the 3rd wire ground.  Had I done this,
then it would have been important to hook it up "backwards", with the LINE
terminals connected to the NST.  But even so, it looks like the magnitude of
the RF ground to 3rd-wire ground voltage may be pushing what the filters
were designed to withstand. 

Bottom line is, the forwards/backwards hookup depends upon whether you are
connecting the RF or 3rd wire ground to the filter case.

Regards, Gary Lau
Waltham, MA USA

Original poster: "Marco Denicolai by way of Terry Fritz
<twftesla-at-uswest-dot-net>" <Marco.Denicolai-at-tellabs.fi>



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

Hi Gary

>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.

Why you don't use the 3rd wire ground?

>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.
>
>Regards, Gary Lau
>Waltham, MA USA

I don't know about pro and cons of "backward" connection, but I can say
something about grounding.

With my old TC and Thor's DC switching power supply I had this
configuration:

1. room with concrete floor and a solid, thick copper sheet embedded in the
concrete (for all the floor surface). Copper was well grounded, of course.
We'll
assume this is a perfect ground.

2. Tank (case) grounded to this perfect ground by a 5" wide copper sheet,
about
5' long.

3. TC grounded to the tank (case) ground (a solid copper bar) by a 5" wide
copper sheet, 10' long.

4. Table covered with aluminium sheet, grounded to the floor by the same
copper
sheet, again about 5' long.

5. Tank sitting on the table, having two wood logs bewteen the two of them.

Running the coil I had 1/2" CONTINUOUS sparking between table and tank rack,
even if both of them were grounded to the SAME POINT by 5' length of copper
sheet!

So there is no doubt: you have such transients on the TC ground, that even a
very low inductance connection will result in generating a (relative high)
potential on the TC ground path and even on the grounding point.

With the EMI filter you want to protect the mains phase and neutral from
potentials too high in respect to the plug (3rd wire) ground. That ground is
definitevely NOT your TC RF ground. If you connect the EMI filter GND to the
RF
ground (I.M.H.O. :) ) you'll possibly achieve nothing or just a damage. The
RF
GND is practically floating to a potential driven by transients and its own
(even if low) impedance.

To limit the potential on plug phase and neutral, I believe you must
connect the
EMI filter GND to your plug (3rd wire), that is:

plug GND: variac, EMI filter, anything you can touch (control panel, etc.)
RF GND: NST filter (on the HV side), NST case, secondary base, strike rail,
RSG
motor case, etc.

Anybody of different opinion?

Regards