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Re: feed thru insulators (fwd)



---------- Forwarded message ----------
Date: Thu, 23 Apr 1998 08:38:24 -0700
From: Jim Lux <jimlux-at-earthlink-dot-net>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: feed thru insulators (fwd)


> 
> 
> 
> ---------- Forwarded message ----------
> Date: Tue, 21 Apr 1998 15:48:48 -0400
> From: Kevin Wahila <kevinw-at-stny.lrun-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: feed thru insulators
> 
> i unpotted my neons and am gathering materials to construct new housings.
> so far i only have some .25" plexiglass (lucite)  i plan on using plastic
> L-bar and nylon nuts&bolts along with acrylic cement to secure the lucite
> pieces together.  so far that seems to be no problem to me.  but i am
> having a problem finding feed-thru insulators for the HV output.  the
only
> place i found that sells them is Daburn, but they don't sell them in
> quantities less than 10.  I've seen them at the nebraska surplus web
site,
> but they are too large.  i was looking in the range of 1-2".  where can i
> get these from?  if i can't, are there any other comparable methods?  

Just use your acrylic (Lucite, Plexiglas) as the feed through insulator. It
is easy to machine, etc. The reason that the commercial units use porcelain
is that it is cheap (in large quantities) and heat resistant (necessary for
UL). You don't have either of these two requirements.  Just make sure that
the "creepage" distance to ground is at least 3 or 4 times the breakdown
voltage in free air. (i.e. for a 15 kV NST, the voltage to ground is 1.4 *
7.5kV = 11 kV) The free air breakdown distance would be about .15 inches,
so make sure that the distance from your terminal to ground, measuring
along the surface of the insulator (i.e. "creeping along") is 4 times that
(or .6 inches). Give it an inch and that will be nice and conservative.

The commercial NST has much bigger creepage distances mostly because they
have to work in the great outdoors, covered with grime and humidity, and
so, require longer creepage distances to avoid shorting.