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Lightning Strikes

> > > I remember a few years back when I was down in Corpus
> and
> > > one of the Corpus TV towers got hit by lightning. My
> Aunt
> > > and Uncle's house are about 5 to 10 miles from most of
> the
> >
> >> Chris from Milwaukee
> >
> It surely seems like everyone has a few good lightning
> stories.
> I've seen AM directional towers take hit after hit and a
> second after, the transmitter would come back up and keep on
> ticking.
>
> It was also a very picteresque site to be driving past the
> World Trade Center in NY one afternoon and see and hear that
> thing get hit in an electical storm.
>
> The sight of an approaching storm will also tend to get you
> down off the radio tower when you're up for a climb rather
> quick.
>
> One strike I remember is when I was the engineering
> supervisor at the Staten Island Teleport. It's a rather
> large installation with several dozen large domestic and
> international satellite antennas with RF and control
> buildings located thoughout a large infield.
>
> One afternoon I was with a few techs working on something in
> "Shelter 6" as we called it. The afternoon sunlight suddenly
> darkened and turned into a dark violet glow, then a rather
> large lightning hit struck something somewhere. From inside
> the equipment shelter I saw a purple arc come dancing down
> the inside of the steel door towards ground.
>
> As soon as the lightning cleared I found many of the motor
> contactors that steer the large satellite dishes had welded
> shut and caused the antennas to move off the birds until
> they came to a mechanical or electrical stop. After
> replacing enough gear to enable the dishes to track again,
> what followed was a heavy week or 2 of overtime repairing
> and replacing chips, transistors and relays mostly on the
> antenna controllers that track inclined orbit satellites.
>
> Some of the other non critical things had gotten zapped such
> as the facility PA system, etc.
>
> More recently at a studio STL tower the strobe light
> controls that light the top obstruction light and some
> computer KVM extenders inside a room where many of the lines
> come in got zapped.
>
> When installing a ground system it is usual practice to keep
> the flow to ground directed in a downward manner for the
> system to be effective.
>
> George Kowal CBNT
>

Of course, your AM transmitter would come right back up unless it was a Harris MW-1A. We had one of those at WRIV. Our experience was that it was stunningly unreliable particuarly when there was lightning in the air. LILCO power surges, lightning, even snowfall would kill off at least one PA module.

Then, in 1998. . .the mother of all lightning strikes. And after one year of trying to get it back up to 1,000 watts. . .we replaced it with a Collins 820D2 1 kw transmitter. The Collins is very stable, very reliable and there is something to be said for the sound of tubes.
 
Good points. I really like Ufer grounds and buried ground rings. Clamps are useless. Soldered joints slightly less so. Cad-weld is best for everything you can do.

I also isolate racks and transmitters from the floor, enter all cabling and power through the tops only, and ground from the top. I don't want the preferred route of discharge to pass through a cabinet -- you need to think about controlling magnetic fields as well as electric energy. I'm big on Polyphasers on ancilliary antennas and telco lines. (T1 CSUs and Burk modem boards tend to become fuses rather quickly without them) Optilators are supposedly even better, but I haven't used them yet.

There is one device used at a transmitter site that will withstand any lightning discharge known to man, and that is the ancient old Western Electric phone with a "Bell System Property Not For Resale" stamp on it. Don't throw it out. You'll need it to call the power company.

> OK
>
> as a veteran of more lightning damage than I care to recount
> (20 yrs in broadcasting + 15 in the 2-way business), here's
> my thoughts on it:
>
> 1) you can never prove you had enough grounding; only that
> you didn't
>
> 2) bond EVERYTHING together.....transmitter, racks, telco
> ground, power company ground with copper strap; ground those
> out as many sides of the building as possible to SEVERAL
> rods at each point
>
> 3) ground guy wires
>
> 4) it doesn't matter if, during a strike, that the equipment
> in the building is at 'X' potential above ground, as long as
> ALL of it is at the same potential
>
> 5) REA grounds suck, big time
>
> 6) ditto telco 'grounds'
>
> 7) if a new installation, overkill it in the plans, then
> double it at install time
>
> 8) pray a lot
>
> E
>
 
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