Subject: Re: Grounds?
From: Terry Fritz <twf-at-verinet-dot-com>
Date: Sat, 23 Jan 1999 11:04:58 -0700
In-Reply-To: <Pine.GSO.3.96.990122115914.19720A-100000-at-xmission.xmission -dot-com>
This is a good question. Here is what I do and it seems to work well.
RF grounds that need to handle high currents (100s of amps) such as in the
primary circuit (safety gaps) or very high frequencies such as the
secondary ground, need to be short, heavy, and directly to a water pipe or
good ground rod. This ground needs to be able to carry hundreds of amps at
high frequency. If the ground is poor the energy will find somewhere else
to go. The household AC wiring ground is NOT good for this. I connect all
the RF Tesla coil parts (safety gaps, secondary ground, neon case,
sync-motor case, and all the stuff right at the coil) directly to this good
heavy ground. If you like to hit a grounded target with the streamer, I
would connect that ground directly to the base of the secondary coil. This
will contain the powerful RF and electrical signals created in the minimum
space. Don't arc to the AC wiring or AC ground - that's "bad".
The only electrical wires I bring back from the coil are the AC neutral
and hot wires for the neon. These go directly to a line filter and MOVs
that are grounded to the normal AC wiring ground (I should probably also
use a filter right at the neon also to keep the RF out of the return
wires). All the variac and control circuits are grounded to the AC ground
system. The sync motor is run from AC but I use the RF ground rather than
the AC ground since there could be an arc to the motor from the primary
system that would have to be dissipated.
If I am using a computer, digital scope, printer, or other high value
equipment. I use another separate ground and AC system for these which
consists of a separate ground rod system (the power is brought through a
long extension cord). The equipment that the scope and computer connect to
is isolated by fiber optics and such so the grounding and AC power for the
high value equipment is completely separate from the control and coil
systems. There are no direct electrical connections to the coil control
equipment or the coil itself. Of course, there is always some risk using
such equipment around Tesla coils but I accept that.
I use MOVs and line filters all over the place but these need to be
grounded to the appropriate system depending on what signals they may see
in the worst case. Basically, if it is very high current, very high
voltage, and/or high frequency it needs to go to the good RF ground. Noise
and electrical safety type grounds away from the coil should be the normal
AC wiring ground.
It is always a good idea to check the AC wiring grounds to be sure they
are properly wired. There seems to be a surprisingly common problem with
that. Contractors really need to be a bit more careful...
People in apartments or that don't have a good RF ground are going to have
problems. I really don't have any good ideas on that. Electrically, if
you run a TC without a good RF ground, all kinds of messy things could
happen. At least be sure the AC ground is very good. If you have NO
ground points at all, it's time to move :-)
At 12:08 PM 1/22/99 -0700, you wrote:
>A quick grounding question. Where should the grounds be connected? I have
>two available grounds, RF and utility. Should all grounding be to the RF
>ground or should something be on the utility?
>Neon transformers and saftey gaps have grounds in the primary, and the
>secondary coil has one. I know the secondary should be on the RF ground,
>what about the primary circuit?
>Logic tells me the RF ground is best, but is seems like that would provide
>a path to connect the primary and secondary together when the saftey gaps
>fire. A second ground rod could provide extra isolation between primary
>How do those doing shows and demos at schools handle the problem? A good
>RF ground is hard to find in those situations.
>Or am I not thinking clearly?
>The recent postings regarding the death of a child on a TC have provided
>extra motivation to bring up my saftey levels (never can be too carefull).
>I want to make sure I'm not putting HV in the wrong places with my coil.