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Re: [TCML] Re: Grounding NSTs (Special Case?)
Jim is right. But it doesn't take much to make a good ground for the
secondary. We've used a screwdriver pounded into the dry desert soil and
caliche with a drip set up to wet the area around the screwdriver, out on
the end of 20 feet of wire. Sounds pretty kludgey (sp?) but it worked fine.
The secondary impedance is pretty high. It's a good idea to have the
counterpoise grounded, hopefully to the actual Earth, but to the green wire
if you can't do that.
From: Jim Lux
Sent: Wednesday, May 01, 2013 3:08 PM
Subject: Re: [TCML] Re: Grounding NSTs (Special Case?)
On 5/1/13 12:41 PM, Brandon Hendershot wrote:
Something else I should mention, since I have no way of installing a real
ground rod, I use a counterpoise as the RF ground in my system.
Everything else in the coil is finished and ready to run, as soon as we
resolve where to ground the NST's (if anywhere (I read that leaving the
NSTs ungrounded causes permanent damage)) I can fire it up for the first
time. Hope you guys can come to the rescue again ;)
Cases of NST to electrical safety ground (aka green wire ground) in the
Bottom of secondary to counterpoise
Counterpoise to greenwire ground.
The idea here is that if you have a spark(s) that touches the primary
(at 15kV) AND the counterpoise (or NST case) at the same time, you don't
want anything you touch to be at 15kV. Think of a spark as a temporary
low resistance connection. So imagine what currents would flow or
voltages would be reached it you took a long cliplead and hooked it from
anything to anything. In particular, you want anything that *might* wind
up connected to the primary (several kV with a fair amount of current)
to be bonded to a good safety ground.
Two reasons to ground the cases..
1) If the case shorts to the power line, you want the case at a safe
voltage to touch.
2) The insulation on a NST is on the HV windings. A spark that bridges
HV to case (e.g. spark to primary and case at same time) will put 15 kV
on the case, and the insulation to the powerline might break down. If
you get a spark going between power line and case, that might be *very
exciting* (for a while)
Reason to ground the RF counterpoise
1) You might touch it. If a spark touches counterpoise and primary at
the same time, and the counterpoise isn't connected to safety ground,
then the counterpoise is at several kV relative to you.
You could, if you like, ground the RF counterpoise to the green-wire
ground using a big RF choke to block the RF, but to let line frequency
power work pass.
On Tue, Apr 30, 2013 at 11:06 AM, Brandon Hendershot <
I know this topic has been beaten like a dead horse, but I can't seem to
come to agreeance with the final verdicts in the archives.
I know that the NSTs should NOT be grounded to safety/third prong ground
since that would inject tons of lovely RF into mains and since the
shouldn't come into contact with them for any reason during operation,
grounding them there wouldn't be any more beneficial than at RF ground.
My only qualms with tying into RF ground is that any strikes to a target
or strike rail would connect the HV streamers to the core of the NSTs.
Nothing about that sounds particularly pleasing in my mind.
So, I'm wondering if the NSTs need to be grounded at all. My NSTs are
situated out of reach of both the operator and any secondary streamers.
(While I feel this may also be an asinine assumption,) I don't see any
for a ground in this situation.
Hope someone can clear this up for me
P.S, I'm thinking about following another list members advice and using
coaxial cable to connect the NSTs to the spark gap and connecting the
shielding of the coax to RF ground to protect the NST's secondaries from
any secondary strikes. My concern with this is similar to what I just
mentioned; any strikes to RF ground would be connected to the coax
shielding. I don't know that I trust the insulation in the coax (which
gaps/cracks from what I can see) to stand off the voltage of the TCs
output, let alone the 7.5kV from the NSTs.
I wouldn't use coax for that..
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