[RFI] ISOBAR

[Roger (K8RI)]

On 9/19/2012 2:24 PM, Dale Svetanoff wrote:
> David,
>
> All I can say about my post is this:  IT WORKS.
>
> YES, the power ground "bounces" up and down to the tune of lotsa' kV, no
> doubt about it, during a strike.  However, ALL of the grounds are bouncing
> at once, and yes there will be some time (phase) differential involved
> because of path length.  A variety of sources I've reviewed over the years
> say that typical products used in residential electrical power distribution
> have an inherent flashover of about 600 V.  Well, if I was seeing many kV
> of differential between my grounds and the power feeders, I should have
> plenty of arc tracks inside my breaker panel, outlets, and so forth.  None
> observed so far.
>
> Remember, the radiated field from the strike envelopes the house wiring in
> one huge common mode coupling of energy.  (My main tower is within 40 feet
> of the shack corner of the house, plenty close to get lots of coupled
> energy.)  Therefore, the actual hots and neutrals are bouncing around with
> common mode induced (especially on that Romex), plus whatever energy had
> coupled onto them via the protectors, rigs, and so forth.  Let us not
> forget that the poor old pole pig is sitting there (75 feet away on a pole)
> getting its secondary side bounced all over, but it doesn't flash over
> because its grounded case is tied to the bouncing ground bus (with power
> company approval).  The bouncing is in relative unison, thus minimizing
> differential potentials..
>
> I strongly suggest that you go on-line and read MIL-HDBK-419A, which
> addresses facility grounding.  You may also wish to consult
> MIL-STD-188-125-1, which concerns nuclear EMP hardening for fixed site
> facilities and to which I was an invited industry representative
> contributor.  Those documents, combined with the QST series of articles by
> Roger Block (of Polyphaser fame), provide a pretty good summary of accepted
> (and proven) techniques for lightning protection of radio and other
> facilities.  I also consulted with engineers from other aerospace companies
> on the lightning transient issues for the F-35 Joint Strike fighter.
>
> In short, I don't think I'm protected - I KNOW I'm protected because when
> the lightning struck, I did not become a carbon block in my chair and none
> of my equipment anywhere in the house was damaged.  In fact, I was able to
> keep transmitting with the stub that was left of my Cushcraft Ringo dual
> bander after the strike vaporized the top 1/3 of the antenna.  Note:  I was
> not intentionally trying to get zapped.  The fact that my station got hit
> as I was conducting emergency traffic related to severe storms was
> coincidental.  I must caution you, and all others: do not try this on your
> own.  Leave "live fire testing" to professionals (whether they intended to
> do so or not).  The only difference between the first strike (in 2008) and
> the second one (in 2009) was that I was not on the air during the second
> strike, but my equipment was fired up and running.  Again, ZERO damage,
> except for another vaporized dual band antenna atop the tower.
>
> The issues you cite in your clip (regarding distance between parts of the
> system) from my post are, quite frankly, ones that I had concerns about
> when building the station and its protection scheme.  Guess what?  I don't
> worry about them anymore.
>
> 73,
>
> Dale Svetanoff, WA9ENA
> Sr EMC Engineer
> E-N-A Systems, LLC
> Specializing in shielding applications, system grounding, and lightning
> protection
>
>
>> [Original Message]
>> From: David Robbins <k1ttt at verizon.net>
>> To: <rfi at contesting.com>
>> Date: 9/19/2012 11:23:09
>> Subject: Re: [RFI] ISOBAR
>>
>> Sep 19, 2012 11:55:43 AM, svetanoff at earthlink.net wrote:
>> "
>> I have 2 aluminum entrance panels: a small one on the south end of
>> the house and a large one on the north end, 54 feet apart. They are both
>> bonded to the perimeter ground. The perimeter ground is bonded to the
>> electric power ground right adjacent to the power entrance, on the south
>> side of the house. My shack is in the NE corner of the basement and is
>> bonded to the north entrance panel. ALL cable I/Os pass thru protectors in
>> one of the two entrance boxes.

People don't realize that even with a properly grounded home, a single 
point ground and entrance panel where *everything* comes in that due to 
the Dv/Dt the voltage differential between rooms on one end of the house 
to those on the other end may be thousands of volts.

Then to complicate matters the routing of telephone lines and cable to 
various parts of the home can make things unpredictable as the 
instantaneous voltages on the branches will vectorarilly(sp?) add at any 
specific spot. The result depending in the location of the strike as 
those locations closer to the strike will rise first.

I gave up and hoped for the best on the CAT5e and CAT6 as I not only 
have the house wired but an additional 3 runs from about mid house to 
the shop that are 130 feet long. The network in both the house and shop 
connects to equipment that also has antennas and power connected AND the 
house and shop are on different electrical feeds.


>> "
>>
>> And this is a perfect example of how people who understand impedance, but
> not lightning transients, think they are protected, but they aren't really.
> That 54' gives enough time for a lightning surge coming from the shack end
> of the ground ring to raise the voltage on the shack equipment cases before
> the lightning protection at the power entrance sees the surge and equalizes
> the power conductors with it to protect the equipment.  remember, the power
> conductors coming from their entrance panel are at their normal 120v level
> until the surge current travels all the way to the panel, 54', through the
> surge arrester there, and back another 54' to the radio room.  that is
> something more than .33usec which can give even a moderate lightning stroke
> time to get the ground voltage up to 10's if not 100's of kv above the
> power ground.  that gives more than enough time for a flashover from the
> ground to the power line through the radio to do damage.

And a really close strike can induce substantial voltages in 
interconnecting wires.  A lightning strike a mile away can induce well 
over a 1000 volts per meter of wire so think what a close one can do. 
How much wire is just in the walls of the house?

73

Roger (K8RI)

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