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Re: NST and GFI ?

Hi Reinhard,
                   I can't give you a reason but I can tell you GFI units
do not like coils.  At the industrial museum Brian&Mike ran at the GFI
breakers kept tripping all night, real pain as they were at the other end of
the building.
That may just have been beacuse they were having strike problems to the
supply transformer.


Regards
Nick Field


> Original Poster: "Reinhard Walter Buchner" <rw.buchner-at-verbund-dot-net>
>
> Hi Ed, Chris, all,
>
> > Original Poster: Esondrmn-at-aol-dot-com
> >> << Original Poster: CTCDW-at-aol-dot-com
> >>  GFI protection is generally NOT considered a good
> >> thing for coils..I have  actually been able to run my coil
> >>(15/60) from a GFI outlet, but I think  that  is the
> >>exception, rather than the rule.
>
> > Chirs,
> > That's good.  Heck, I have an old refrigerator out in the
> >garage that won't even run off of a GFI outlet.  Too much
> >leakage current I guess.
>
>
> Having posted this before, I still CANNOT find a single reason
> why a coil canīt be powered off a GFI outlet. I run my coil off
> a GFI outlet, too, and have never set the GFI off due to coiling.
> Using a NST that encorperates a GFI internally is another thing,
> esp. if the GFI checks the secondary side of the NST (as some
> German units, that I have seen, do). This wonīt work, but on the
> low (mains) side, I see no way that a normally operating TC will
> trigger a GFI.
>
> A GFI does nothing more than to check that voltage *coming* from
> Ph is returned properly via the N line (and not via Grnd). It does
> NOT measure the voltage ON the ground line in any true way.
>
> I have a 3 phase 380V/40A/30mA GFI in my shop and basement
> house wiring. I always power my TC from this part of the house
> and my GFI has never tripped because of a running coil. It really
> shouldnīt either. Why? Well the GFI is designed to trip under two
> circumstances:
>
> a.) fault current from N to Grnd.
> Although usually residing at the same potential, it is possible
> (doesnīt hold true for U.S. residential wiring, as there is no
> three phase wiring) that N may actually float above "zero"
> volts, esp. if R-S-T (3 ph.) arenīt loaded equally, which is
> why you donīt want a short between N and ground.
>
> b.) fault current from Ph to Grnd.
> Quite obviously, you donīt want to "raise" the potential of
> the ground line and this isnīt the way the current should
> (the GFI thinks, ooops, some has his fingers on the wiring
> and trips) flow. Like when some gal insists on using a
> hairdryer IN the bathtub and then drops it into the
> water ;o)
>
> It should NEVER trip, when the current flows from Ph-N,
> which is exactly what we have in a TC circuit. There (should)
> NEVER be any current flowing from Ph to Ground in a TC,
> as there is NO direct connection bewtween Ph and Grnd. In
> other words, the secondary is (AND should be) completely
> isolated from the mains wiring. Once via the primary and
> secondary and once via the HV xformer. The fact that you
> are (esp. if you donīt use a dedicated ground) "nailing" a few
> hundred kV into the ground canīt trip a GFI, because there is
> no relation to the mains phase and this is the only thing that
> the GFI really tests.
>
> Personally, I feel a little *safer* with a GFI, because it CAN
> and SHOULD trip under the following circumstance:
>
> a.) As I coil outside, it enhances the safety, if I ever should
> get *caught* in the primary (i.e: mains) wiring of the HV
> circuit. Of course, it wouldnīt help me on the HV side of the
> power circuit, as this is, once again, isolated from the mains
> part via the xformer.
>
> A GFI COULD trip under the following circumstance:
>
> a.) You get an arc from the secondary to the primary (not the
> strike ring) and this overvolts the HV secondary of the
> transformer, which in turn arcs to the primary winding of the
> xformer (aka back to the mains). However this is highly
> unlikely and IF it does happen, youīll need to worry about
> more than just a tripped circuit breaker or GFI ;o(((.
>
> Coiler greets from Germany,
> Reinhard
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