RE: blown NST's

["Rick Richard" <ollopa-at-jps-dot-net> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

I don't think your NSTs will work very well no matter what you do, until you
fix the shorts.  Hopefuly you only have some carbon tracking, and your wires
aren't melted.

I have "de-potted" one of these resin transformers once.  I have some pictures 
of it, too.  You will have to use a hacksaw or hammer-and-screwdriver to cut 
away the metal case.  I found that soaking this resin in kerosene for a day
would soften the resin enough to chip away a centimeter of it.  You have to
repeat this process of soaking for a few hours, chipping, and soaking again 
for a couple days.  Eventually you'll be able to break off large chunks, and
this is the point at which you have to proceed carefully!  Even though you can 
break off huge pieces, right down to the NST core, don't do it!  The secondary
windings are soaked with that resin.  If you take off a large piece, you will
likely tear the secondary windings apart and make the weekend's labor 
worthless.  you might want to use a large-toothed hacksaw to carefully cut the
resin away from the core.  

--Rick--



On 07-Sep-00 Tesla list wrote:
> Original poster: "Richard Barton" <richardbarton-at-caving5.freeserve.co.uk> 
> 
> Hi all
>       For around 4 years I've used 3 NST's (12/30 each) hooked up
> in parallel, using a static gap, with no problem. Recently I build a rotary
> gap..... now all three NST's seem to have blown !
> They are all shorting to the metal case internally.... one of them has a
> real bad DEAD short, and knocks the trips out immediately.
> The other two seem to knock the trips out after a minute or so, they
> have a fairly high leakage to the cases, but it's not a dead short.
> Now, I've read all about this business of de-potting NST's, but these
> ones seem to be potted in resin ! At least , it looks like resin to me.
> It's very hard to even scratch, and the stuff is a pale yellow colour, so
> I reckon it's impossible to de-pot these. They are "RICCI" units.
> Can someone confirm that these are resin-potted ?
> Further to this, if I can't de-pot these, is it not possible to used them if
> I
> either-
> A. Use them without the cases earthed (Dangerous ?)
> or....
> B. Cut the cases off with tin-snips, and peel the metal off (Also dangerous
> ?)
> These units are housed inside a cabinet, and could be mounted on rubber
> mountings to isolate them from ground, thereby getting rid of the tripping
> problem, but will they work properly if they are not earthed ?
>                                               Richard Barton.