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Re: the physics of a neon sign
>. The old metal flex conundrum,
>thank God we're now officially able to use plastic conduit without needing to
>do legal research to justify it. That was tortous circular reasoning. You
>needed the metal conduit to protect from the wire burnouts that were caused
>by the metal conduit, but didn't need it if you didn't use it because the
>only reason for the burnouts and arcing was the existence of a ground plane
>hugging a 15kV wire. Sort of like overloading a plane with parachutes in case
>the plane went down from being overloaded, or something like that. About time
>someone would recognizet that the only way the wires get burned out is from
>exposure to a gnarly ground surface only 1 millimeter away.
>
>Have made a good living replacing 3/8" metal flex conduit by 1/2" plastic
>smurf (indoors), which, working with Carlon's VP I got listed this year,
>finally. Outdoors, I use Carflex liquidtite.The metal's not the solution,
>it's the problem. I've never had any arcing problems as long as I have used
>it. I also do a nice service I call "dividing down" the circuit for one of
>those buzzing, wire burning, overloaded (tubing wise) signs, where I take out
>the 15kV transformer and install 2 9kV transformers, splitting the circuit in
>half. I usually do this in connection with removing all the metal flex EMT
> and replacing it with ENT. This has never failed to turn a problem sign into
>a faithful performer. Never a fire, unless someone else messes with it.
Jeff,
We had quite a go-round early-on in the list about installation techniques.
At that time I went on at great length about my own "tried-and-true"
bulletproof techniques, which pretty much make the same claim as yours: many
signs in the field without failure, never a fire, six years in business
doing signs night-and-day, and a good living made by "curing" the ills of
chronically troubled (competitor's) signs. The techniques I use are pretty
much the same as yours (smaller transformers, short transformer leads, load
to 80% max with a meter, etc) with one notable exception: I ALWAYS use metal
flex, either 3/8" or 1/2", and I ALWAYS use generic bottom-of-the-line GTO,
and I've not had any GTO burnout on any signs ever (oops I take that back:
just before I left Hawaii I had a GTO failure -- it was a two-year old sign
where I inexplicably used a 15k on an indoor PK housing -- musta been out
of twelves and in a deadline rush). (And, of course, this doesn't count the
sign installations done for other companies, who typically overload the 15k
trafo and then require servicing once or twice per year).
This leaves me to conclude that it's not so much the conduit (be it metal
or plastic) but the other techniques that have been discussed (though
clearly the type of casing makes a big difference when using large
transformers, or when a long run from the transformer to the first tubes is
unavoidable).
-Ted Pirsig