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GFI Protection

 >>  The new NEC also states that ground fault protection must be included on
most instalations. Kind of makes mid"point/circuit'' grounding difficult. <<

 Hey Dave,

 Why do you think this?  A GFI only looks at what current comes back on the
neutral compared to what went out on the hot. If it is very close to the same
amount it assumes that there is a "leak" to ground where some of the current
going in is not making it back. Usually a correct assumption. As I said
before, in a current loop you the current returning should be the same as what
went out. I don't see where Mid-Point or Kenny's End-Point <g> ground scheme
should be a problem. There shouldn't be any more leakage and probably less than
a non-midpoint scheme.

 >>  Ted's note on keeping the GTO between the trans (secondaries) and the neon
short I also think is real important.  I worked on a border tube job (GTO in
metal conduit) with 15's and on each leg whin using a mA meter, the meter
would start wild jumping around stuff when the leads were over about 6 feet
long.  In talking to some transformer manufacturers about this they said it
had to do with corona in the conduit and the trans thought it was going direct
to ground (hey, I'm just a mechanical engineer, maybe some of the EE"s on the
neon list would please comment <<


 This is a LENGTHY subject (no pun intended...ok, maybe it was<g>). I've been
bitching for years on the use of metallic conduit for HV leads. The only way
to keep corona problems down is by judiciously figuring in that extra
capacitance effect into the load calculations. It is true that using smaller
size transformers will keep down the voltage since they will only go to their
maximum voltage rating. For instance, if you use a 6000V. it will only put out
a maximum of 6000V. or 3000V. if it is a midpoint model. Using a 7500V.
non-midpoint (which most are) is the SAME as using a 15000V. (Just to add to
the confusion). If you are overloaded (which you would be if you followed the
neon footage chart) on the transformer with GTO in conduit then you are
putting out those spurious harmonic spikes we mentioned and the voltages of
those peaks can become very, very high in the nature of 30,000V. or so. And
that is true even with a smaller sized transformer. At the same time that UL
and NEC are considering FAILURE modes as dogma for normal operation, they
don't consider that "normal" operation could CAUSE those modes. Certain to be
continued.....

 >> Also using the best silicone for secondary to neon leads in time will save
you money on service calls. If you're real cheap, use the black GTO fro the
end runs back to the ground on the transformer. <<

 Good advice for those who MUST use GTO in conduit or greenfield. As MC stated,
there is a lot of corona discharge associated with those overloaded and highly
spurious GTO runs in that conduit. Given that it is an enclosed space as far
as ventilation goes I would be very concerned about the abundant ozone that is
being produced as well as the ultra-violet from the micro-discharges all along
that system. This would certainly quickly break down any PVC or other plastic
insulation leaving all sorts of problems in that space. Like I like to
describe the UL's thinking "WHEN the fire starts it will be contained by the
conduit". The use of silicone is not only recommended but should be the ONLY
type allowed for this use. You can use regular GTO as Morgan stated for the
grounded returns as long as there is no failure of the ground connection that
isn't serviced for some time. The tubes should drop the voltage to safe levels
but as we have all seen those spurious spikes happen when the load goes high
and they could still present a problem. I'm SURE that UL has tested for this
though <g>.

 BTW, it didn't connect when Jacob welcomed MC to the list. I was still trying
to figure out who it was... too much ozone on the brain.  Thanks for the
reprints, Morgan...good bathroom reading. (Just kidding) and I'm glad to see
you made it here with us. I like all of the graphs and data to back up what
you say.  Sure beats "this sign caught on fire because it wasn't grounded
properly". HUH??!?  Lucky for me this is a closed arena and I can only receive
that many flames <BG>.






  E-mail from: Tom Biebel, 20-Dec-1995