Original poster: Sparktron01@xxxxxxxxxxx
Excellent question! First Terry Fritz had the idea first of placing an
RFI ballast choke between the "safety ground" (grounding conductor)
and the case of a NST or MOT farm. Lets assume a 120V, 20A branch
circuit capacity and you want the touch voltage to be less then 30Vrms
(not making these numbers up, anything below 42V peak or 30V rms
is considered "touch safe" if exposed). Also assume maximum let through
current is 40A before OCD opens (fuse, CB or PCB trace your pick).
This calculates out to a 60Hz impedance of 0.75 ohm (30V/40A), and
a theoretical calculated impedance (if all inductive) of 1.25k ohms at
100kHz (linear increase with frequency , Z = wL). This calculates out
to ~ 2mH inductance, which could be easily built using a ferrite ring
or toroid, and high current wire.
> But how do we bond it to ground? After all, a
> short of any of the hots to the conduit will make the whole thing
> hot, and a long piece of flexible metal conduit on a concrete floor
> isn't necessarily going to trip any breakers or blow fuses to
> indicate the fault. And it isn't safe, either, since the conduit is
> connected at the panel end and therefore accessible during normal
> (plugged in) operation. So we can't leave the conduit floating.
> One end (at the coil?) to RF ground? Remember, the theory is to
> have low impedance to RF ground. But we have other concerns as well.
> So other end (at the control panel?) to house ground? But then what
> if it takes a streamer hit?