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Re: Grounding Question.

Original poster: Vardan <vardan01@xxxxxxxxxxxxxxxxxxxxxxx>

Hi Glen,

The safety ground for the 120 or 220VAC is great for 60Hz line current and grounding all the sheet metal and such. But it is no good for the RF base current ground of the secondary coil. The RF current from the secondary should go to directly a ground rod or other direct earth connection.

I would ground all the metal work and AC power stuff like the transformers to the AC line safety ground to protect against shorts in the usual way. For the secondary base connection, just get a few foot long length of ground rod or pipe and pound it into the ground or connect it to some other good direct earth ground.

On rare carefully thought out "little" coils the AC ground might be used. But for most coils, the RF ground needs to be a short direct path to the earth " totally separate" from the AC ground. RF on the AC ground might really mess around with any electronic stuff on the line and the ground wiring is terrible at RF frequencies anyway.

Some older than 5 years old coil plans are sort of "odd" and need to be looked at in a more modern light where "real" engineering is used 8-)) Typically they are filled with errors that have been corrected in modern times. But for now, ground the base of the secondary to a nice earth ground rod.

Feel free to ask about any other odd things with the plans you have. In general, someone got it to work that way. But if something does not seem right, we can help.

I bought a few coil plans from Information Unlimited too 30 years ago. I think some of those plans are still the exact same ones they had then!! They should still basically work, but some things are commonly done differently now days.

I assume yours is the BTC4 here:


They mention:
"A metal control panel is connected to earth ground along with the secondary output coil return, reducing line voltage shock hazards."

I think they got that "WRONG"!!!!!!!!...

Sometimes RF currents from the coil are not grounded well by the AC ground. Small RF currents can get on the control panel metal work. So a separate "THIRD" RF ground rod is used just to ground the control panel from the RF. However, in that case, the control panel RF ground and secondary RF ground are NOT the same!!! The control panel is grounded buy the AC ground and an RF ground rod, and then the secondary is grounded to a "totally different" RF ground rod. But for you coil, just the AC ground for the control panel is fine. The third RF ground for the control panel is more for coils like this:


This has been mentioned here on the list by myself and others before. I think that might have gotten back to the plan makers here - and gotten misinterpreted. :-(((



At 11:33 PM 7/16/2006, you wrote:
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.