Re: NST Safety and grouding

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Jason by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jasonp-at-btinternet-dot-com>

Hi Jim,

> I am new to the list and am in the process of building a 6" coil
> initially powered by a 15kv/60ma NST. I have read  many contrary
> references regarding RF protection and secondary spark protection. I
> have also read NOTHING SHOULD BE GROUNDED except the control panel (-at-
> household ground) and the strike ring and secondary base (-at- RF ground).
> The concern seems to be potential coupling BTW the primary circuitry to a
> secondary streamer of ionized air adding many amps -at- 60 hz /15kv + cap
energy
> which would likely be lethal if contact was made to anything living
> other then Godzilla.  I am planing to build a Terry Fritz NST protection
> circuit that depicts the Xformer case grounded to the RF ground, your
opinions?
I always ground my NST to mains ground, not RF ground. This is because if
the case is grounded to RF ground and the RF ground fails, the case of the
NST will float at high voltage, and inject HV into the centre tap of the
xfmr, and we have 'blue sparks from mains socket' scenario all over again. I
keep the NST mains grounded for that reason. The 'Terry Filter' on the other
hand is grounded to RF ground, for obvious reasons, (i.e. MOV firings).

> Assuming a RF grounded strike rail, some pertinent
> newbie questions follow:
>
> 1. Does the RF grounded  NST + Center taped spark also protect against
> this scenario?
Yes and no. For the protective SG to fire the primary strike has tp pass
through the caps, which some people say damages the caps. Personally I think
that caps are safe from primary strikes, because by nature the capacitor
junction will short out RF energy, as such from the topload od a TC. The
centre grounding of the NST does not have any effect on the PSG and the
strike rail.

> 2. Do most coilers place the NST under the Primary deck?
Many coilers place the NST under the deck - I dont, because I cant be
bothered to build an enclosure

> 3. If 2=yes, how do you protect 110v feed from a potential strike at
> higher powers?
Firstly, you can use a shielded cable, secondly, you give the coil a
breakout point, thirdly you give it a ground rod, or all of the above.

> 4. If 2=no, ditto the HV feed lines ( the spark gaps make sense here)?
On my coil, the HV lines are actually coaxial cable. I use UMR47 (?)
transmitting coax cable which has one end of the coax screen grounded to RF
ground. the inner core is the HV line, the outer core is RF ground. That way
if you get a line strike, then it just gets dumped to ground.

The one thing that you are forgetting is that if you have a strike rail then
you will not get line strikes, because it will naturally go to the ground
rail. Another tip - keep the primary wiring as small as possible. Amazingly
high currents flow, and have a habit of melting wires :)

> I have a 20a Powerstatand EMI filter for the control panel.
> I am also considering purchasing an isolation Xfomer as well.
I wouldnt bother with that filter - it won't work. For an EMI filter to be
effective, you need it to be rated as close to your power level as possible,
for example a 2KVA neon farm should have an 8A filter on it.

> I would appreciate you experience on these issues. Next, I'll bug ya
> about EMI, pulsed energy across costly electronics, and unhappy
> neighbors :-) Sometime the road I'll try to offer something back. Thanks
As long as you use a properly grounded EMI filter, line interferance should
be minimal. Unhappy neighbours are more of a problem, I suggest you run your
coil when they are not around, or give them a demo :)

Good luck,
Jason

> Wavetuner (Jim Mora)
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