Re: [TCML] Primary Support Materials

[Gary Lau <glau1024@xxxxxxxxx>]

It's not clear that folks are in agreement on whether PVC is prone to
surface tracking.  Here's my thoughts.

If PVC were inherently prone to surface tracking, we'd all be in trouble, as
pretty much all of our secondaries are wound on it, right?  Surely a
secondary coil has a far higher voltage gradient than a primary support.

I think Ralph's account of a PVC antenna support succumbing to carbon
tracking is not surprising, given that it occurred when it was covered with
dew.

FWIW, I had carbon tracking on some (dry) Lexan primary supports - I had too
many unused primary turns adjacent to a grounded strike ring.  Anything will
surface track, then carbon track, if it's carbon-based.

That said, it's hard not to notice the discoloration of white PVC near a
spark gap.  If that brown stuff is more conductive than PVC (don't know),
perhaps there is a higher risk of surface tracking on PVC near the gap,
although I've never heard this reported.  But secondary coils are
sufficiently shielded or distant to not be affected.  I'm guessing the same
is true for primary supports as well.

Regards, Gary Lau
MA, USA



On Tue, Aug 24, 2010 at 9:35 AM, David Rieben <drieben@xxxxxxxxxxx> wrote:

> Hi Greg, all,
>
> Yes, I certainly agree that PVC is farily prone to
> tracking, especially when used in key insulative
> components of a fair sized VTTC (personal ex-
> perience with this). I've also discovered that it
> does not fair too well over the long term as the
> containment tube for a multiple "RQ" style sta-
> tionary spark gap, as white PVC tends to de-
> velop a yellowish-brown tinge, which is brittle
> and tends to be somewhat conductive, in the pre-
> sence of the strong UV radiation from the SG.
> However, I have had absolutely no trouble along
> these lines using it (gray electrical grade PVC) as
> primary support rails in my large coil, which is now
> about half way into it's 7th year of existance. And
> I don't think that it's really THAT ugly ;^))
>
> David Rieben
>
>
>
> ----- Original Message ----- From: "G Hunter" <dogbrain_39560@xxxxxxxxx>
>
> To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
> Sent: Monday, August 23, 2010 10:12 PM
> Subject: Re: [TCML] Primary Support Materials
>
>
>  I'll second that motion.  I've been using PVC pipe and zip ties for my
>> primary supports since the 1990's.  I've never noticed any particular
>> propensity for PVC to break down and carbon track--not any worse than any
>> other plastic.  This is the quickest, cheapest way for the non-machinist to
>> build a primary support.  If you require an appearance-grade coil, do
>> something else.  The PVC pipe method isn't pretty.
>>
>> Greg
>>
>
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