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Re: skin effect
Arturo:
One point here. I realize that in Europe the maximum voltages are 10kV.
However, here in US the maximum is 15Kv. This is a standard condition. I
happen to agree with you that these are perhaps too high. I usually prefer to
use no more than 9kV, but there are times where it is unavoidable, and in
these situations special precautions are needed.
For one thing, you seem to feel that the parasitic capacitance of the wiring
will drain the power of the transformer, especially for long wiring. This
would be true if the old convention of using only metal conduit for wiring,
especially flex metal conduit, was still in effect. However, it is far
superior, and we finally have justified this technically and put it in code,
to use non-metallic conduit. In this event, you may use wiring of any length
whatever. The losses are negligible if you eliminate the capacitance using a
dielectric material in the conduit. I personally use Carlon Blue Flex for
interior, and Carlon Liquidtite Carflex for exterior applications. I have
wired signs and lighting with wiring lengths of over 150 ft with no adverse
effects, using non-metallic conduit. Wire burnout becomes negligible.
Reliability is greatly enhanced this way. There is practically no drop in
power, since the current of neon is so low. The effect is like a transmission
wire: how many miles do you have to go before you lose a kilovolt from a 30ma
current? Answer: Lots. I have wired up many residential covelighting
installations using these techniques, and have had practically no service
calls after installation this way. However, in these jobs, we only use 9kV.
This minimizes the corona effect, which thresholds around this point.
So you see, it's not so crazy.
Regards,
Jeff Golin