[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: Grounding Question.

Original poster: "Gerry  Reynolds" <gerryreynolds@xxxxxxxxxxxxx>

Hi Glen,

Just to summarize what others have said and add third comment:

1. Secondary base, center terminal of safety gap, and strike rail (if used) need to be grounded to a separate RF ground (not connected to mains ground). I like to also ground the NST (if located under or very near the TC) to RF ground. Any control panel/variac/sheet_metal that you may come in contact with during operation needs to be grounded to mains ground.

2. Chokes in series with the NST HV bushings is NOT recommended. Use the Terry filter (RC low pass filter to keep RF off the NST - see archieves)

3. The schematic shows C1 and C2 from line (and neutral) to mains ground. This is suggestive of a line filter that I do recommend. However there is a limit on the size of C1 and C2 because there is a limit on how much current can be in safety ground for safety reasons in case safety ground opens up. Line filters usually use a common mode choke to turn any common mode stuff on hot and neutral into a differenctial mode signal that can easily be filtered with a cap between HOT and NEUTRAL (no limit on size).

Gerry R.

Original poster: "Glen McGowan" <glen.mcgowan@xxxxxxxxx>

I'm building a TC from the attached schematic. From the looks of the drawing I'm double grounded. The secondary is grounded to the mains and earth. The NST's are all grounded via a shared grounding plate which is mains grounded.


C1 and C2 are there to limit noise fed back into the house wiring (some of it at least). I understand that grounding the secondary to the grounding plate can produce lethal currents but is there any advantage to doing this? This may be a rhetorical question. I assume the secondary would "choose" the earth ground before it reached the mains ground because earth would be the shortest distance. But according to the drawing the NST's HV and LV's are both using the mains ground as is the secondary (has a "choice" of using mains or earth).

I apologize if the post was hard to follow. I've scratched the same spot on my head for the past hour. It's starting to bleed.