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Re: SAFETY GAP CONNECTIONS



Original poster: "Barton B. Anderson" <bartb@xxxxxxxxxxxxxxxx>

Hi Ed, All,

A thought just ran through my brain pan as the Merlot passed by:

Not all NST's are capable of tying the hv terminal low (rf ground). If the secondary center tap is tied to the case, then you would only have 1/2 voltage from the NST (the rf ground side would be null and void). In those cases, a 3 terminal gap would be necessary. However, all potential and distribution transformers should be fine with the hv terminal tied to rf ground.

Just thought I should mention that since I referenced the method.

Take care,
Bart

Tesla list wrote:

Original poster: "Barton B. Anderson" <bartb@xxxxxxxxxxxxxxxx>

Hi Ed,

I showed my preference hookup in the related post. I prefer a 2 terminal system to be at rf ground, one output tied to rf ground, and the case of the transformer at rf ground as well. Same would go with a 3 terminal safety gap system. The rf ground side is noisy and I don't think anyone would argue against that, but the noise is not reflected back on mains ground when mains ground ends at the control power cabinet and rf ground is at the transformer case. I agree, the case center tap and center terminal of the safety gap should "not" be separated.

However, I don't see a perfect system out there. There are reasons on both sides of the old argument "where does mains ground end and rf ground begin". For myself, I want them separated. So, I chose to keep all hv situations on rf ground and the low voltage side at mains ground. For this to occur, mains ground must end at the control panel.

Take care,
Bart

Tesla list wrote:

Original poster: Ed Phillips <evp@xxxxxxxxxxx>

From some of these discussions I get the impression that there is a recommendation that with a "two-gap" system protecting an NST the center terminal of the gap should go to "an RF ground" SEPARATE from the center tap (usually case) of the NST. That sounds wrong to me as I can't see how such a connection would necessarily protect the transformer from inadvertent over voltage conditions. Connection to the center tap AND a good RF grounds makes more sense.

Ed