Re: Pig setup help.

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

Original poster: "Gerry Reynolds" <gerryreynolds-at-earthlink-dot-net> 

  Hi Bart,

Original poster: Bart Anderson <classi6-at-classictesla-dot-com>

 >>Transformer grounded to mains ground (green wire):
 >>
 >>Benefit:  transformer fault (like primary to case short or secondary to
case
 >>short) may draw excessive current and blow breaker (note that the balast
for
 >>a PIG or PT may not allow this to happen unless ground fault protection
 >>is used).  Case is safer, however one still has the bushings that can
kill.
 >>
 >>Disadvantage:  A strike to the TC primary (transformer secondary) could
 >>flashover to the case and thus the mains ground and kill sensitive
 >>components (TV, stereo, etc) also plugged into the mains.

 > It is possible, but this is true with both configurations, including
 > floating configurations. The lowest impedance will feel the brunt of the
 > hit.

I agree that the strike current will take the lowest impedance, but I think
we need to keep in mind that the strike current is trying to return to the
base of the TC secondary (RF ground).  If we make sure the lowest impedance
path is to RF ground, we can be very sucessful in keeping the mains ground
out of the picture.  With a NST, I believe any strike that gets to its HV
bushings will arc to the core long before it finds its primary (due to
construction).  The core is grounded to the case and if the case is grounded
to the TC secondary base, the return path will be provided.

A strike to the TC primary, when the transformer is grounded to mains ground
and the TC secondary is grounded to a dedicated path to earth ground, will
almost certainly make its way to mains ground (unless there is a flashover
between TC primary and TC secondary before flashover between transformer
secondary and transformer case occurs).


 > Also, consider strike rings tied to rf ground (for all those folks who
 > use them).  A probability factor comes into play by an increase
 > frequency of hits (and you will get an increase in primary directed hits
if a
 > strike ring is used, and at times, the primary will get hit as well (espec
ially
 > for coils with poor field control). I just prefer to minimize the
possibility's.

YES, this is a concern.  The strike rail needs to be between the TC primary
and the topload to intercept the strike.  This of course shortens the
distance between the topload and a target.  Field control is important and a
raised topload (with a corona ring to protect the top turns of the
secondary) may be necessary to not increase the frequency of primary
directed streamers.

Take care,
Gerry R

 >>Transformer grounded to dedicated earth ground (aka RF ground):
 >>
 >>Benefit: a strike to TC primary that results in flashover to transformer
will
 >>directly return to the secondary ground and not contaminate mains power.
 >>
 >>Disadvantage:  transformer fault could result in a HOT case and no blowing
 >>of the breakers if the dedicated earth ground is not adequate.  If
adequate,
 >>the protection should be just a good as mains ground, but still no
 >>guarantees for the balasted pig or PT unless ground fault protection is
used.
 >>
 >>I think one should define danger zones in their system design.  If the
 >>transformer is within the danger zone,  grounding to the dedicated earth
 >>ground is OK.  If outside the danger zone, the transformer should be
 >>grounded to mains ground and the bushings protected from accidental
 >>contact.
 >>
 >>One persons opinion,
 >>Gerry R