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Re: Random TC Questions

Original poster: "Gerald  Reynolds" <gerryreynolds@xxxxxxxxxxxxx>

Hi Jim,

I'm studying your reply carefully trying to understand a different point of view. I'm glad you didn't use building code in your arguments cause all of my sources seem to indicate that the code applies to the building and any permanently installed electrical equipment. The TC (I believe we both agree here) is not in any way building code complient considering the exposed hazardous voltages (primary, secondary, etc). Perhaps it is useful to talk about two situations: inside where earthground may not be close at hand, and outside where it is available.

Original poster: "Jim Lux" <jimlux@xxxxxxxxxxxxx>

> Do you really think that tying the strike rail and secondary base to the
> green safety wire is going to make the TC any safer??

I think that the counterpoise, or anything that you will be standing on,
that is connected to the bottom of the secondary should be tied to
protective ground (green wire). The idea is to minimize the possibility of
injury or fire in the case of a fault.  It's not unheard of for the 110V or
10+kV to short to TC components (something falls on the coil, you get a
flashover, etc.).  If I am standing on the concrete floor, or happen to be
touching something with a grounded metal case, AND I happen to be touching
the TC counterpoise at the same time, I don't want to be fried.

I agree it would not be pleasant to be standing on a counterpoise that got energized to a hazardous voltage by a fault while touching an object that is grounded. I think we both agree that the base of the TC needs to be grounded and that something will act as a conterpoise whether it be natural or artificial.

If INSIDE, the floors are of questionable grounding and if they conduct for any reason (wet wood, concrete), a fault could make them hazardous with respect to ground. I think this may be a good reason for an artifical counterpoise that is well grounded. If people are standing on the artifical counterpoise (and they dont need to be), it would be safer to have it grounded to the green wire if other things in the room are grounded to the green wire. In general, high power coils probably should not be inside, but if they are, the artifical counterpoise should probably be 3D (to protect the walls, floor, and ceiling from a strike that could start a fire. One thing that should be realized is that the green wire goes back to the breaker panel where it connects to neutral. This node is then grounded to earth by a connection to a water pipe (existing code when our house was built) or to a rod in the ground (apparently todays existing code). Therefore a counterpoise grounded to a waterpipe or to a rod in the ground can be the equivalent of the safety ground.

If OUTSIDE, your counterpoise is earth and the TC should be directly grounded to it. If all objects and persons are at a safe distance, there is no fault that can raise anything outside this safe distance to a hazardous voltage.


If you think you
> need a strike rail then I'll let you touch the strike rail or base > during
> operation. If you tie it to the green safety wire then any strike to
> objects earth grounded will cause the return current to come back thru
your
> house wiring to find its way back to the base of the coil. That could
kill
> your computers plugged into the mains even if turned off. If you think
> this is a code issue, then this has got to be an issue of "can touch" > and
> certainly not "intended to touch". Then what do you do about the top
> load??? That can be touched too. You, as operator, have the
> responsiblility to see that it is not.

Sure.. If you can set up your system so that it's entirely floating, and
that a strike never goes anywhere near a "grounded" object, you can not
safety ground the secondary.  However, that's a fairly big challenge.

I never advocated a floating system. I too believe that the coil base and strike rail need to be grounded. My biggest concern when using the green wire as a ground is return currents coming thru the house wiring.



As for RF return coming back through the "greenwire ground", that's why you
should put a choke in the connection.  The safety ground is for 60Hz, not
for RF.  However, whether it's explicitly connected or not, the streamers
can still put significant voltages into the house grounding system by
inductive coupling. The streamer is a fairly fast, fairly high current
transient (i.e. high di/dt) and the area of the loop is fairly large
(secondary, topload, streamer, whatever it hits, return path to secondary).

Two problems with a choke. They are never ideal, they have parasitics and can resonate and pass RF energy. Secondly, they can only discourage RF return currents in the green wire if an alternate return path is provided for. If no alternate return path exist, all of the RF base current will flow thru the green wire ground whether or not the choke is present.

> If the green safety wire is used to ground the TC (like for indoor
> operation where an earth ground is not close at hand) then, as you say, > a
> counterpoise will be necessary to intercept any strikes and allow its
> return current (and RF return current) to go directly back to the base > and
> not thru the house wiring.

If you don't have a counterpoise, where do you think the RF return currents
are going?  Why would they not follow the green wire ground back through the
interwinding capacitance of the HV transformer to your coil?

Without an artifical counterpoise (btw, I'm not opposed to use of such a counterpoise, just very cautious about the use of the green wire for grounding the TC), the walls and such will be the counterpoise and the RF currents (both conduction and displacement) will flow from them into earth (that's what they are connected to). So the TC base will need to be earth grounded to allow the RF current to return. This return path could be the green wire or it could be a dedicated wire to earth ground. I prefer to minimize the currents in the green wire by providing this alternate path.

Gerry R.