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Re: To ground or not to ground?

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

Hi Dirk,

I missed a comma in my reply and think it was misinterpreted. The variac housing should be grounded to safety ground. I consider that to be part of the power supply box and the operator will come in contact with it during operation. The NST was excluded from this definition and assumed to either be under the TC primary or right next to it.. If the NST is with the TC, it is no longer a safety issue since no one will be near it during operation. For this configuration, I personally ground the NST to RF ground to help protect the mains wiring in case of a secondary to primary strike. Outdoor operation is also assumed where earth ground is the counterpoise. The variac controlled power cord from the power supply box to the NST can be a two wire cord. If a three wire cord is used, the safety ground wire should not be used. Same can be said for the fan power cord.

If indoors where a RF ground is not available, as Jim says, a conterpoise is required and needs to be grounded to the greenwire. Its function in this case is to collect all the RF currents caused by the secondary fields and return them to the secondary base to keep them out of the mains ground. This, however, is not perfect so power levels need to be kept low as well.

Gerry R.


Original poster: "Dirk Stubbs" <dirk@xxxxxxxxxxxxxx>

Thanks Gerry.

I have a total of three wires coming from  my control box.

1 - Variac controlled line
1 - Constant 120V line
1 - Neutral

Grounding of components in control box done through house ground except for
variac chassis as you mentioned.

Sounds like I have it all right.

Thanks again,
Dirk Stubbs

-----Original Message-----
From: Tesla list [mailto:tesla@xxxxxxxxxx]
Sent: Thursday, October 27, 2005 1:10 PM
To: tesla@xxxxxxxxxx
Subject: Re: To ground or not to ground?

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

Hi Dirk,

All the equipment that someone could normally come in contact with
during operation should be grounded to greenwire safety ground.  This
would include your power supply box defined to not include the NST
and the variac housing. The EMI filter needs this safety ground as
well to function.  I'm not sure what your over current protection is
(maybe a fuse or ckt breaker), but if it is in the power box located
with the operator and needs ground, then safety ground is the one to
use.  RF ground should not come into areas where people would be
during operation.  The NST located at the coil (underneath it lets
say) should be connected to RF ground and not to mains ground (in
case there is a secondary strike to the TC primary).  If the MOVs are
part of the Terry filter, they should be grounded directly to the NST
chassis as well as the cap portion of the filter.  The NST should be
powered by the output of the variac where as the fans should be
powered by a constant 120Vac and not go thru the variac.

Gerry R.

>Original poster: "Dirk Stubbs" <dirk@xxxxxxxxxxxxxx>
>
>I have a question regarding grounding of my TC components.  I am
>wiring up my power supply box which contains a variac, emi filter,
>and overcurrent protection. It will supply power to my NST and spark
>gap fan.  Some of the components in the power supply  require a
>ground such as the  EMI filter(10VR6), MOV's, and even my variac
>housing(would be nice). What ground do I use in my power supply? My
>house ground or my RF ground?   I know not to use the house ground
>for my RF ground. Does this also apply for grounding in my power supply
box?
>
>I looked in my NEC under article 250 but found nothing about
>grounding Tesla Coils or their power supply circuits. ;)
>
>Thanks,
>Dirk
>
>
>