Original poster: FIFTYGUY@xxxxxxx
In a message dated 3/21/06 8:04:53 PM Eastern Standard Time,
tesla@xxxxxxxxxx writes:
> I would also put a line filter on the primary side
>of a MOT or NST and a RFI choke (low impedance to 60Hz, high
>impedance to RF) on the ground between the case of the NST and a
>Terry filter on the HV side.
Dave, what kind of filter would you feel appropriate for the
RFI choke here? Would a ferrite bead/ring type as used on power
cords, with a couple turns of the wire connecting NST case and
Terry/RF ground be sufficient? Or are you thinking a larger
air-core coil? What value range?
>Grounding/bonding is a critical exercise to industrial equipment;
people >have
>DIED by having defective safety ground bonds.
Only because they touched something that was "plugged in" and
that they thought would be at safe potential while they were in
contact with it. Doesn't solve the problem with things still
plugged or hardwired in, or that store energy , such as caps or
batteries. And since we don't touch the high voltage side of our
Tesla coils while they are plugged in or while the caps are
energized, this shouldn't be an issue with NST cases unless the NST
is located at the control panel.
So let me throw this *new* question out there:
Even if you put the NST at the coil proper (in "high voltage
land"), you still have to run power (LV) wires to it. So how do you
ground things in case of a secondary strike to these LV wires?
I'm running my LV wires in a flexible metal gooseneck conduit,
so a secondary strike will hit the conduit instead of the power
wires. These power wires include the "hot" to the NST from the
variac, the "hot" to run the SRSG from the phase control, the "hot"
to run the gap cooling fans, and a neutral common to all three.
Obviously, a secondary strike to any of these would be bad. But the
conduit will be a relatively large piece of tubular metal laying on
the floor, so I'm hoping it will have low impedance to RF ground
and thus protect the wiring inside.
So far so good? 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?
And we can't bond it to *both* house and RF ground, because
that would be like tying both together. Maybe if the conduit was
itself an RF choke?
Perhaps the conduit should be nonmetallic up to the point of
the maximum expected reach of RF and streamer hits, but metallic
and tied to RF ground in the vicinity of the coil?
-Phil LaBudde