Connect counterpoise to cage. There’s really no inside or outside at these frequencies.
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> On Oct 15, 2026, at 18:51, George Schramm <georgeschramm5@xxxxxxxxx> wrote:
>
> Ok, good to know on the emi filters. I'll look them up to be sure. The coil
> is designed to run at 131khz, although hopefully they'd have some use
> blocking hf (mhz) transients generated by the spark gap firing.
>
> As far as the faraday cage, should the inside be grounded to the
> counterpoise, and the outside to safety ground? Or leave the cage inside
> disconnected from the rf ground and just surrounding the coil?
>
> Thanks for your help!
>
>> On Thu, Oct 15, 2026, 3:54 PM Jim Lux <jim@xxxxxxxxxxxxx> wrote:
>>
>>
>>
>>
>>
>>
>> Faraday cage or simulacrum is he way to go. You could use something like
>> 4" reinforcing mesh for both the counterpoise and the walls and roof of the
>> cage. Or whatever is structurally, aesthetically, etc suitable.
>> You'd want to have that cage connected to "green wire" earth ground for
>> safety - if someone touches it, with bare feet on floor, you don't want a
>> shock.
>> Isolated things near a tesla coil running can pick up a surprising charge.
>>
>> I'd not worry about a ground rod.
>> RF choke on power wires is a good thing. The Corcom filters *might* be
>> ok. You need to look up the data sheet and see what frequencies they are
>> good for. If your coil is running at 100kHz and the filter is a low pass
>> with a cutoff of 1 MHz, that doesn't do much good. Those filters are
>> designed for particular applications - some are good for low frequencies,
>> others are looking for 10s of MHz (e.g. to keep computer noise out of a
>> power line or box)
>>
>>
>>
>> On Thu, 15 Oct 2026 12:33:00 -0700, George Schramm <
>> georgeschramm5@xxxxxxxxx> wrote:
>>
>> Hi all,
>>
>> I'm currently building a dual mot asrsg 6" tesla coil, and i'm debating
>> different grounding scenarios and am looking for advice.
>>
>> Ideally i'd like to run the coil in my garage, with a, say, 4'x4'
>> galvanized metal roofing counterpoise, surrounded by a Faraday cage that
>> also connects to the counterpoise, as well as the strike rail and mot cores
>> and safety spark gap. The coil would be completely encased.
>>
>> Another option I was thinking is running a standard copper ground rod
>> outside, no faraday cage, in this instance I was wondering if I can connect
>> my mot cores to mains ground, maybe with a rf choke on the mains ground
>> line to discourage rf from the power supply flowing back in through the
>> mains ground wiring. Is this acceptable?
>>
>> The coil will run dual mot with a voltage doubler, 500pf 40kv bypass caps
>> and 2x 1kohm 225watt resistors forming a low pass rc filter. Along with a
>> safety spark gap connected to rf ground.
>>
>> I also have two 30a Corcom emi filters, one at the input of the control
>> box, and one on the output of the 20a variac.
>>
>> Power input is limited with a 120v 20a circuit, (us)
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>>
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