RE: [TCML] Main ground vs RF ground

["Lau, Gary" <Gary.Lau@xxxxxx>]

The only place for using the mains-ground is for objects that one is likely to touch while energized.  The purpose is in the event that there is a short between the HOT line and the thing that one might touch - to provide a path to ground so that the fault current trips the breaker or fuse and neutralizes the threat.  

In a Tesla coil, there should be no objects beyond the variac case or control cabinet, that one might touch.  Only the variac case and control cabinet should go to mains ground, and the NST case must not be connected to that.  The NST case should be considered off-limits to touching (it will hurt the whole time...).  Unlike in a neon sign application in a pizza shop where a customer could reasonably make contact with the NST case, we and those under our supervision, should NEVER touch the NST case or any other part of a Tesla coil.  It is dangerous by nature and will never be UL-approved!

Using both an RF and mains ground for things that are RF-hot (NST case), is not conservative, it's just wrong and serves no purpose as far as minimizing RF interference.  One could argue that it may make the coil safer should there be a fault, but doing so destroys your effort to reduce EMI.  The Terry filter schematic is 100% correct.

Regards, Gary Lau
MA, USA

> -----Original Message-----
> From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
> Behalf Of chuck
> Sent: Thursday, November 19, 2009 11:47 AM
> To: 'Tesla Coil Mailing List'
> Subject: RE: [TCML] Main ground vs RF ground
> 
> "But since you are asking about NST's and the Terry filter,
> if you are running a single low powered NST with a Terry Filter, you may
> not have too many issues to be concerned about, but if you are running
> multiple NST's, I would consider a separate RF ground to be safe... "
> 
> Would I be correct to infer that using separate RF and mains grounds would
> the more conservative way to go? That is, while I run a low risk using a
> common ground with one or more NSTs, that risk is reduced if I use two
> grounds: a mains ground and an RF ground? If so, I need to alter my Terry
> Filter.
> 
> Shouldn't somebody issue a pen and ink change to the Terry Filter schematic?
> 
> 
> 
> 
> 
> -----Original Message-----
> From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
> Behalf
> Of BunnyKiller
> Sent: Thursday, November 19, 2009 12:17 AM
> To: Tesla Coil Mailing List
> Subject: Re: [TCML] Main ground vs RF ground
> 
> 
> Hey Chuck...
> 
> In the majority of instances, the RF ( or secondary base wire) should
> have its own "RF" ground rod. Hooking the secondary base to the "house"
> ground can lead to problems with items that contain circuitry boards...
> and thats about everything as far as appliances go... computers, ovens,
> stoves, refridgerators, garage door openers,  touch lamps ( the kind you
> touch to turn on) will eventually fall prey to the wrong grounding
> techniques. But since you are asking about NST's and the Terry filter,
> if you are running a single low powered NST with a Terry Filter, you may
> not have too many issues to be concerned about, but if you are running
> multiple NST's, I would consider a separate RF ground to be safe...
> Replacing the stoves controller board isnt cheap... ask me how I know
> about that one ;)
> 
> There are some instances in which the NST is wired with the case ground
> on the center tap of the unit... IIRC grounding the case and secondary
> becomes "weird"...
> not too sure about this situation....  see if someone else has that answer.
> 
> Scot D
> 
> 
> chuck wrote:
> 
> >Some coilers say that the NST may be grounded to the mains ground and
> >that the secondary of the TC should be grounded to RF ground and
> >emphatically declare that the two should never meet. Others say ground
> >is ground and it doesn't matter where the unit is grounded as long as
> >it is grounded. The famous schematic of the Terry Filters shows the NST
> >and the TC sharing a common ground.
> >
> >So which is it? Should the Terry Filter schematic be altered? Or not? I
> >hope for first lights by Thanksgiving so I need an answer ASAP.
> >
> >asimov13647@xxxxxxxxxxxx
> >Stuck in the (now infamous)
> >23rd NY Congressional district
> >
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> >
> >
> 
> 
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