Good thoughts. Today I disconnected the RF ground from the RSG motor housing because of the concerns that I had about imperfect RF grounds. I will also build a RF grounded "target" near the motor as you suggest. Another thing I have done is to wire a MOV in parallel with the 120 volt RSG power line. The MOV is located back in the control cabinet. A streamer somehow coupling into the 120 volt RSG power line may blow the MOV which is good. If the MOV fails as a short then it will trip the 15 amp circuit breaker in the RSG control module in the power cabinet. I have gone back and forth on whether to use MOVs or not because they are really only for short duration occasional power line spikes. I also have some really beefy MOVs on the 240 volt mains line coming into the control cabinet as a last resort if EMI filtering is ineffective.
----- Original Message -----
From: "Gary Lau" <glau1024@xxxxxxxxx>
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Sent: Friday, August 11, 2017 5:57:47 PM
Subject: Re: [TCML] RSG grounding
Hi Steve,
Yes - very definitive thoughts! The RF ground should not be connected to
anything that doesn't have bullet-proof high voltage insulation to the
mains. Despite the connection to what is hoped to be an absolute ground,
there exists very high voltage transients on the RF ground node, relative
to the mains and everything else not in the TC circuitry, particularly when
there's a streamer connection to the RF ground. I've never heard of any
discussion on how to measure the RF impedance of an RF ground, but I
suspect it's pretty high. I once fried a lamp dimmer used to throttle
power to a blower for my spark gap, and I had the metal case tied to RF
ground. It's understandable to want to protect the motor from a strike - I
would recommend doing that with an RF-grounded target between the motor and
the likely direction of incoming streamers. Let the motor case just float.
Regards, Gary Lau
MA, USA
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On Fri, Aug 11, 2017 at 1:09 AM, Steve White <steve.white1@xxxxxxxxx> wrote:
> Does anyone have any thoughts on connecting the RSG motor housing to the
> RF ground? This is my current set up. What I am trying to protect against
> is the possibility of a streamer hit or an accidental connection to the
> primary tank circuit to the motor. It seems that without the RSG housing
> being connected to RF ground, any streamer strikes to the motor could
> couple an extremely high voltage back into the house wiring via the 120
> volt power line for the motor. On the other hand, since my strike rail is
> also connected to the same RF ground, any deficiencies in the RF grounding
> rod resistance to the ground could result in the streamer strike going
> through the motor anyway because of a lower impedance path.
>
> I should mention that I have been running with the RSG motor housing
> connected to RF ground with no apparent ill effects to the motor even
> though I get a lot of hits to the strike rail.
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