RE: NST Safety Gap Question.

To: tesla-at-pupman-dot-com
Subject: RE: NST Safety Gap Question.
From: "William Parn" <parn-at-fgm-dot-com> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)
Date: Wed, 19 Apr 2000 11:41:09 -0600
Approved: twftesla-at-uswest-dot-net
Delivered-To: fixup-tesla-at-pupman-dot-com-at-fixme
Greetings,

> -----Original Message-----
> From: Tesla List [mailto:tesla-at-pupman-dot-com]
> Sent: Tuesday, April 18, 2000 1:37 PM
> To: tesla-at-pupman-dot-com
> Subject: Re: NST Safety Gap Question.
> 
> 
> Original Poster: "J. B. Weazle McCreath" <weazle-at-hurontel.on.ca> 
> 
> At 11:27 AM 17/04/00 -0600, you wrote:
> >Original Poster: "William Parn" <parn-at-fgm-dot-com> 
> >
> >
> >Greetings All,
> >
> >I picked up a second 9kv-at-30ma NST and decided that
> >I now will definitely need a safety gap.  So I 
> >hooked one up and paralleled the NST's.  The gap
> >constantly fired, it did not fire when connected
> >up to one NST directly.  So I doubled the spacing
> >of the gap and then it still fired often.  
> >
> >So I am wondering what are the basic rules for setting
> >the safety gap so that it only fires upon a primary
> >strike, or something potentially equally devastating?
> >
> >Or does it sound like I maybe have another problem, like
> >maybe to small a wire in the primary hookups?
> >
> >By the way my variac is electrically tingling me
> >with the two NST paralleled.  Will this stop if I
> >stop using the house ground for the NST's and variac?
> >
> >Many Thanks,
> >Bill Parn
> >
> Hello Bill:
> 
> The simplest and most effective way to set the safety gaps is to connect
> them, and only them, to your transformer(s) and set the gaps close.  
> They will fire initially, meaning you need to increase the gaps slightly
> and equally and try again.  Repeat this until you find that magic spot
> which is just beyond the point where they fire.  Secure them at this
> spacing and you're all set.

That is what I did initially, then when it would not stop firing I opened
it up to twice that distance and it still fired 1 to 2 times a second.
Maybe I need to redesign a better one, it is built inside a piece of
2" ID PVC pipe.  I built it in the form of a peace sign, instead of 
three equally spaced pies.  Maybe that is where it is going wrong.

> 
> Regarding the "tingling" off your variac, this indicates that it is hot
> with R.F. or possibly a ground fault exists.  Make sure that your T.C.
> secondary bottom, your center terminal of your safety gaps, and the
> cases of your N.S.T.'s are all connected together and to a GOOD ground
> separate from the third pin ground of your power cord.  The ground wire
> of your power cord should be connected to the metal frame of the variac,
> any metal parts of your control panel, and the ground terminal of your
> E.M.I. line filter only.

Okay sounds like a good plan to me.  I believe I have all the parts now
to design it just like you stated above.  One thing that I am still 
questioning a little is whether or not to connect the NST's up to the
same ground as the secondary though.  Would it maybe be better to have
a another isolated ground for the safety gap and the NST that are not
being pushed around as much as the ground hooked up to the secondary?

Would a isolation transformer help anywhere in this schematic?

> 
> 
> 73, Weazle, VE3EAR/VE3WZL
> 
> Listening: 147.030+ and 442.075+
> E-mail:    weazle-at-hurontel.on.ca
>            or ve3ear-at-rac.ca
> Web site:  www.hurontel.on.ca/~weazle
> 
> 

Many Thanks,
Bill Parn