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Re: [TCML] Re: Grounding NSTs (Special Case?)



Connecting the secondary > to the counterpoise > to the safety ground, why
use a dedicated RF ground at all if I'm just going to be pumping RF into
green wire ground?


On Wed, May 1, 2013 at 3:08 PM, Jim Lux <jimlux@xxxxxxxxxxxxx> wrote:

> 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
> power cord.
>
> 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.
>
>
>
>
>
>
>  Thanks,
>> Brandon H.
>>
>>
>> On Tue, Apr 30, 2013 at 11:06 AM, Brandon Hendershot <
>> brandonhendershot@xxxxxxxxx> wrote:
>>
>>  Hi All,
>>>
>>> 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
>>> operator
>>> 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
>>> need
>>> for a ground in this situation.
>>>
>>> Hope someone can clear this up for me
>>>
>>> Thanks much,
>>> Brandon H.
>>>
>>>
>>> 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
>>> has
>>> 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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