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GFCI trouble with Tesla use

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coaster_chris

Wed Sept 26 2007, 06:18PM

Registered Member #359 Joined: Sat Apr 01 2006, 09:27AM
Location: Utrecht, The Netherlands
Posts: 16

Hi all,

I've pulled my Tesla out from under a thick layer of dust, because I will be needing it during a Halloween event in October.

When I first tested the coil over at my dads place (last year) I was having some trouble with the ground fault circuit interrupter tripping every now and then.
I moved the coil over to my moms, where I used a counterpoise under the coil. And it all worked great! So I have had the coil up and running for ages over there, whiteout any trouble.

I was fiddling around in the garden again at my dads house, and there I hit the strange problem again!
The coil worked fine for the first couple of seconds, but again the GFCI was tripped.
Now I have no idea where the problem could be, because the only aspect where the situation differs is that I use a grounding rod which I stuck 1 meter into the ground, as to a counterpoise which I had used so far.
I cant really relate to this, as being the source of the trouble. :S

Then there could be multiple options, but because I don't have the option to find out what the answer is by blowing the GFCI a couple of times, I kinda was hoping maybe one of you guys had an idea. :)

The only things I could think of changing are:

- I think the most logic thing would be to ground my NST, which I have never actually done... and also wasn't recommended by some Dutch coilers. Since it is center tapped the core should be 0 volts.

- Replacing the rod by a counterpoise, as this has always worked so far... and by changing this it suddenly triggered the GFCI. But I can't really see that as being the reason for triggering the GFCI. because how could there be electricity leaking away in the secondary part? :s

- I have a bottom plate made out of 8mm MDF in my coil which all components rest upon. And the bottom plate is placed on the lawn.
My MMC rests on the bottom with the contacts which have 8Kv across them. This has always worked fine, but I know it is pushing it a bit. But then again there is no sign of direct arcing to the ground.

- Someone I know had this same problem a bit back, that was because his NST was arcing to gnd. but there just isn't the option of that here because my NST is insulated from gnd. en all connections are made with thick wire all floating in mid air and not touching anything.

Any thoughts on that? :)

Nik

Wed Sept 26 2007, 11:21PM

Registered Member #53 Joined: Thu Feb 09 2006, 04:31AM
Location: Ontario, Canada
Posts: 638

My advice would be don't use a GFCI plug.
They are very sensitive to electrical noise and not suited at all for use near a tesla coil. At work we frequently trip the GFCI breakers and recepticals with walky-talkies, I can only imagine what the noise from a tesla coil will do to.

...

Wed Sept 26 2007, 11:59PM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

As you probably know, a GFCI trips when it finds there there is a difference in the current on the hot/nuetral (or other hot if you are in a country with 220v). The current required to trip it is very small, on the order of 10ma.

When you run a tesla coil with a ground rod, you are getting a small DC offset, probably only a few mA, in the secondary current, which is enough to cause a ground fault.

When you use the counterpoise there is no where that the DC can go, it just charged up the metal plate, so you can't trip the GFCI.

ArcLight

Thu Sept 27 2007, 03:28AM

Registered Member #341 Joined: Thu Mar 23 2006, 07:41PM
Location: Northern Illinois, USA
Posts: 69

I have run my grounded SGTC for hours while plugged into a GFI outlet with no problem. The only filtering in my circuit is a Terry filter (thanks Terry,) but ran the coil for quite some time with no filtering what so ever with no problems. I know that the GFI functions, because my early coils used saltwater caps and I slopped some of the water once causing the outlet to trip. However, I have a GFI outlet in the kitchen that pops constantly with only a (two pronged, plastic cased, mounted on a wood cabinet) can-opener plugged into it.

Maybe you should change the outlet and see if the problem goes away.

Regards, ArcLight

coaster_chris

Thu Sept 27 2007, 11:09AM

Registered Member #359 Joined: Sat Apr 01 2006, 09:27AM
Location: Utrecht, The Netherlands
Posts: 16

We have the GFCI installed in the main fusebox, so it won't be possible to bypass it. (without breaking safety seals and stuff ;) )
We have them installed in all homes over here, they're triggered at a 30mA current difference. So it donâ€™t think the DC offset will be this large.

Here's a link to the type installed:
GFCI

Otherwise I guess I should just stick with a counterpoise, but this isn't the best solution.

ArcLight

Thu Sept 27 2007, 10:04PM

Registered Member #341 Joined: Thu Mar 23 2006, 07:41PM
Location: Northern Illinois, USA
Posts: 69

I never meant to suggest by-passing the GFI. My only objective was to determine if the problem is a defective/hair-trigger GFI or the coil. Once that is determined you'll have a better idea of the steps needed to correct the problem.

Where I live here in the States we are required to have GFI in the kitchen, bathroom, garage, and any outlet within 6 feet of a sink. This can be accomplished with a GFI breaker or by placing a GFI outlet first in the chain of outlets. Having the GFI built into all the breakers makes the job of trouble shooting much easier. Just swap the suspect breaker with a different one of the same rating in the box. It only takes a couple of minutes and if the replacement continues to trip, you know that your coil has sprung a leak.

Just as a side note, my NST is grounded to mains ground while everything else (coil, safety gap, targets, etc.) has it's own ground rod.

Regards, ArcLight

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