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Registered Member #3904
Joined: Sat May 21 2011, 10:32AM
Location:
Posts: 28
I'm wondering how best to ground my NST. At the moment it's connected to mains ground and the secondary has its own RF ground (see A).
Would it be a really bad idea to connect the innermost winding of the primary to RF ground and disconnect the NST's mains ground? (see B) If I was using something other than a center tapped NST, would this be the preferred configuration?
Alternatively, should the center tapped NST be connected to RF ground? I'd really like to understand the pros and cons of each.
Registered Member #4052
Joined: Thu Aug 11 2011, 04:43AM
Location: IN ,USA
Posts: 69
In my experience with SGTC's the RF ground likes to arc to things. Which shows that it is carrying high voltage. Admittedly I have never had a good RF ground to properly earth my spark gap coils, because they have to be ran outside and need an extensive ground.
However even with a proper ground I do not think that you will want the chance of high voltage feedback into your NST. I think that no matter what you do with the RF ground you will want your NST on mains ground to protect it from shorting out.
After all NST's can be quite fragile. If you were using a pole pig it probably would not matter if you even had anything grounded.
I connected mine to mains ground, and secondary to copper pole in yard. Hee hee I draw the schematic almost everywhere, but I draw it a little bit different.
Registered Member #3885
Joined: Sun May 15 2011, 12:47AM
Location: Newton, Massachusetts, United States
Posts: 94
Your MST MUST be connected to mains ground via its center tap at all times! If mains ground = RF ground, then that's even better, but you should never leave your entire NST's case floating at several thousand volts.
Registered Member #3904
Joined: Sat May 21 2011, 10:32AM
Location:
Posts: 28
Daniel Kramnik wrote ...
Your MST MUST be connected to mains ground via its center tap at all times! If mains ground = RF ground, then that's even better, but you should never leave your entire NST's case floating at several thousand volts.
What's the most likely bad thing that's going to happen if it isn't grounded? What scenarios are going to kill it?
Registered Member #4052
Joined: Thu Aug 11 2011, 04:43AM
Location: IN ,USA
Posts: 69
If you let your NST float at high voltage then there is going to be a huge difference in voltage between the primary winding and the iron core of the transformer. the NST's primary is only meant to be 220v from ground. I would assume that the primary shorting out would be far worse that the secondary. Best case senario for this type of failure is probably a flipped breaker and ruined transformer, worse case would the transformer catches fire and/or sends high voltage back into mains.
As Daniel Kramnik it would be ideal if your RF ground was efficient enough to be equal to mains ground. However from what I have see this is rarely the case.
Also in a NST the secondary is only insulated to half the output voltage because the midpoint is grounded. For example a 10Kv NST will always have one terminal at +5Kv and the other at -5Kv. So grounding one side of the transformer may also cause a problem with that.
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Where to ground NST?
