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Re: the physics of a neon sign

>all crapped up after being exposed to a high electric field. The same field
>is concentrated and made larger for a given voltage V by a smaller distance d
>between  the wire voltage and ground potential in the denominator of this
>(E/d), so if you have a 3/8" metal conduit, you are dicing with death on wire
>burnout compared with your chances when you use only 1/2", but I don't

But isn't the wire touching the wall of the 1/2 conduit at nearly every
point down the run?   Seems to me it would even with 1" conduit unless you
had it suspended down the middle somehow.

>recommend either IF you go above 7.5-9kV. The exact threshold depends on some
>other conditions such as humidity, wire diameter, dirt, etc.. Dirk doesn't
>have this type of problem because in Europe, they are not looney enough to
>use our higher transformer voltages, so he faces a different set of rules and
>he can get away with murder compared with our problems using our largest 15kV
>transformer.

As you mention here, 15kv has different properties than 7500kv, and IMO
needs a different set of rules.  A GTO-less installation would alliviate
most of the problems 100%.

I think it's interesting to look at the electric power industry.  They pump
20, 40, even 100kv  (at hundreds of amps) down nearly every street in the
country.  And they use porous wood (which gets wet every rain) and bare
wires.  It's ceramic insulators and air-spacing that make this arrangement
very reliable and safe.  It usually takes a major natural diaster (tornado,
etc) to create an arc that actually ignites something else.

If you are forced to go high on transformer size by a large neon
>footage in your sign, use ENT, not EMT, you will find your day (and year)
>will go better, much better. That's why your strategy is fine, too.

I still don't trust ENT.  I've seen GTO in a channel letter installation
arc and burn right thru it.  I know that ENT itself does not conduct, but
how do you know someone won't lay something conductive on top of it after
you're gone?  Metal wall studs, EMT from future electrical work,
line-voltage romex or wires, etc.

   -John

______________________________________________________________________________

John Anderson
Mega Volt Neon, Inc.  - Austin, TX
dead@netcom.com
Host:  Internet Neon Mailing List