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radioman

Mon Oct 04 2010, 01:08PM

Registered Member #3026 Joined: Fri Jul 23 2010, 02:46PM
Location: Los Angeles, California, U.S.A.
Posts: 54

Can someone tell me the advantages/disadvantages of using two different grounding sources for my 7,500 volt NST tesla coil? I have the transformer case connected to the house power main ground line and a copper stake in the garden for the secondary coil and the center electrode of my safety gap. Herr Zapp said something that makes me think this is not the best idea. Also, what do the stars by the members names mean??

Thanks, Radioman

modularduck

Mon Oct 04 2010, 02:16PM

Registered Member #3094 Joined: Tue Aug 10 2010, 03:12AM
Location: portland, or
Posts: 30

Stars are based on number of posts if im not mistaken.

As for grounding, using a seperate HV ground will keep kick back from going into you houses electrical system and can improve performance i think. I have recently been having this issue with my homes alarm system being bugged by errant high voltage feeding back into the houses system and i don't really want to fry it. a good grounding rod driven through the foundation should fix this. I hope.

HV Enthusiast

Mon Oct 04 2010, 11:53PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

Thats a great question Radioman.

You want a dedicated RF ground (i.e. your copper garden stake) for the secondary as the peak ground currents in your secondary RF ground can be very high, as well as include lots of RF hash, for lack of better words.

A good ground connection prevents large voltages from developing across the RF ground (especially if you did use household earth ground where other equipment could see those voltage spikes), and a dedicated ground connection adds some isolation of the RF noise between your coil and the household earth ground.

Hope that makes sense.

Sulaiman

Tue Oct 05 2010, 05:29PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

Do not connect the center electrode of your safety spark gap to any earth other than the NST earth or you will get strange symptoms.
e.g. safety gap firing for no obvious reason.

Connect ALL earths to the utility/NST earth except maybe for the TC secondary and strike rail which may go to a separate earth.
If you are going to run indoors then use the utility/NST earth ONLY
If you are going to run outdoors then connect the TC secondary base and strike rail to 'real' earth.

Think about it .........
the arcs from the top of the secondary want to connect to the bottom of the secondary
indoors the arcs will go to utility earth then have to find their way back to the bottom of the secondary.

radioman

Wed Oct 06 2010, 01:37AM

Registered Member #3026 Joined: Fri Jul 23 2010, 02:46PM
Location: Los Angeles, California, U.S.A.
Posts: 54

Sulaimen

Thanks for your comment . But I donâ€™t really understand why I will get â€œstrange symptomsâ€ if my safety gap and my NST take different routes to ground. Isnâ€™t ground just ground?? What if I connect the transformer case, along with my secondary coil and the safety gap ground electrode, to my garden stake? Then only my metal control box, along with itâ€™s inclosed line filter, will be connected to my house wiring ground. I just donâ€™t feel happy about having the safety gap use house wiring. Am I wrong?

Sulaiman

Wed Oct 06 2010, 03:49AM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

Yes

ScotchTapeLord

Wed Oct 06 2010, 01:23PM

Registered Member #1875 Joined: Sun Dec 21 2008, 06:36PM
Location:
Posts: 635

The ground in your safety gap should be your house mains, since that is the ground around which your NST is balanced. If you're worried you should use an EMI filter on the NST's power input.

HV Enthusiast

Wed Oct 06 2010, 06:51PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

radioman wrote ...

Sulaimen

Thanks for your comment . But I donâ€™t really understand why I will get â€œstrange symptomsâ€ if my safety gap and my NST take different routes to ground. Isnâ€™t ground just ground?? What if I connect the transformer case, along with my secondary coil and the safety gap ground electrode, to my garden stake? Then only my metal control box, along with itâ€™s inclosed line filter, will be connected to my house wiring ground. I just donâ€™t feel happy about having the safety gap use house wiring. Am I wrong?

Because your house EARTH ground (Which your NST is connected and powered from) is not necessarily the same potential as RF ground. And RF ground, during operation and depending on impedance of your ground connection, could be bouncing all over the place.

radioman

Thu Oct 07 2010, 12:13AM

Registered Member #3026 Joined: Fri Jul 23 2010, 02:46PM
Location: Los Angeles, California, U.S.A.
Posts: 54

Thank you, moderator!

Russell Haley

Thu Oct 07 2010, 06:18AM

Registered Member #2478 Joined: Mon Nov 23 2009, 03:24AM
Location: Texas A&M University
Posts: 47

The house earth ground is attached to a ground stake somewhere, most likely on your property. The NST outputs are referenced to this ground. If you connect the safety gap center electrode to a separate ground stake, the current path will be NST output ->spark gap -> center electrode -> earth stake -> soil -> main house earth stake -> safety ground for entire house -> NST casing -> NST secondary ground return. This is most certainly not a desirable condition.

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