Re: NST and GFI ?
On second thought, you're right. There shouldn't be any inherent
current imbalance because the spark is an induced current. What goes
in on the hot side of the primary should come out on the neutral side
of the primary regardless of arcing (unless, of course, you have
arcing to either of the hot or neutral lines). I've had problems running
Tesla coils off of GFI outlets (they trip). I have a prototype GFI which
I could measure a current imbalance that exceeded the trip threshold (as
opposed to RF noise or something).
One thing comes to mind... My transformer was center tapped (but I didn't
ground the case--at least not deliberately). I was using a safety ground
(third prong) as the ground for my secondary. Suppose for the moment that
my transformer case wasn't as isolated as I thought. It is concievable
that there could have been a current (e.g. from the ground to the
transformer case) that was causing the imbalance I was reading and trip
the GFCI. There wasn't anything obvious (such as an arc striking the
transformer--internal arcing in a transformer is usually, but not always
pretty obvious). I don't suppose any other ideas come to mind as to why I
could measure a current imbalance.
On Wed, 16 Feb 2000, Tesla List wrote:
> Original Poster: "Jim Lux" <jimlux-at-jpl.nasa.gov>
> Not quite.. I think an earlier post from Reinhard laid this out pretty
> well.. The arcs and corona coming off the secondary are not "referenced"
> to the primary circuit, but to the RF ground (which might be the third
> prong). The current in the primary of the NST will be properly balanced
> and the GFI won't trip.
> > From: Tesla List <tesla-at-pupman-dot-com>
> > To: tesla-at-pupman-dot-com
> > Subject: Re: NST and GFI ?
> > Date: Tuesday, February 15, 2000 11:48 PM
> > Original Poster: spam_proof-at-worldnet.att-dot-net
> > That stands to reason. In the US, GFI/GFCI's are set to trip if the
> > difference between the current coming from the hot and going back into
> > neutral is more than 5 milliamperes. If you're using (like me) a ground
> > such as a drain pipe, that is current which is coming from the hot, but
> > not returning on the neutral. Two good ways to get around this:
> > 1. Don't use a Tesla coil on a GFI outlet. Ground fault circuit
> > have a higher tolerance (can't remember the exact current off the top of
> > my head) and will be able to take a bigger Tesla coil.
> > 2. Although I don't recommend it, you can use the neutral (prong on the
> > left) as a ground and make sure all of your sparks hit the neutral on the
> > Tesla coil side of the outlet (e.g. using a neutral from another outlet
> > or "upstream" from the outlet won't do). Keep in mind that St. Elmo's
> > fire is current going to ground, so just because you don't see sparks
> > doesn't mean you aren't leaking current. I would recommend against this
> > because, inter alia, a substaintial number of outlets are reverse-wired.
> > If you do this and you are reverse wired, you'll have 120v exposed metal
> > you might not be aware of...touch your Tesla coil chassis while you are
> > leaning against a radiator or some other grounded object and you're
> > There are other problems associated with using the neutral as a ground,
> > but I won't bother going into them.
> > On Mon, 14 Feb 2000, Tesla List wrote:
> > > Original Poster: Esondrmn-at-aol-dot-com
> > >
> > > In a message dated 2/13/00 5:56:59 PM !!!First Boot!!!,
> > > writes:
> > >
> > > << Original Poster: CTCDW-at-aol-dot-com
> > >
> > > GFI protection is generally NOT considered a good thing for coils..I
> > > actually been able to run my coil (15/60) from a GFI outlet, but I
> > > that
> > > is the exception, rather than the rule.
> > >
> > > chris
> > > >>
> > > Chirs,
> > >
> > > That's good. Heck, I have an old refrigerator out in the garage that
> > > even run off of a GFI outlet. Too much leakage current I guess.
> > >
> > > Ed Sonderman
> > >
> > >