[Elecraft] potential of static damage

Fri Mar 14 21:45:06 2003

For those of you worrying about grounding, part of the problem in
understanding what goes on is that the amount of charge delivered by a
lightning strike completely overwhelms the ability of the material in
the "ground" to "absorb" the strike.

For most of our everyday uses, the ground is a huge electron sponge
that behaves as a huge neutral. Not so in a lightning strike.

The capacitor effect formed by a charged cloud overhead can accumulate
the opposite charge over hundreds of acres below. When a strike
occurs, the short circuit to the capacitor occurs JUST AT THE POINT OF
THE STRIKE.

This means that all the charge meant to neutralize acres of opposite
charge is present in a tiny area around the point of the strike while
the opposite charge is still spread over the acres.

The next thing that happens is that the huge charge at the strike, and
the opposite charge all over the acres flow toward each other to
neutralize each other. This can occur with an ionized path in the
ground itself (killer of buried telephone cables) or in a "wave" that
spreads out over all or a large part of the compass.

THAT is when all of the damage occurs that is not precisely at the
point of the strike. This is sometimes called induced, though that is
a bit of a misnomer.

There will be a very large current that will spread out from the
strike point, that does not come to equilibrium until the opposite
charges are satisfied.

This ground charge equalization current is subject to the same ohms
law and impedance issues as any current.

What goes wrong if ALL THE GROUNDS IN AND AROUND THE HOUSE are not
tied together?

Remember that the charge is moving AWAY FROM the strike point to
equalize. The house may have a crawl space or a basement. Either is a
BLOCK to current. The crawl space will be drier than around the house
(or you wish it was) and less conductive. The basement is just an
impassible block.

Grounds on the strike side of the house will charge up to whatever the
ground is as the charge "wave" goes by. If that ground is directly and
heavily connected to a ground on the other side, the charge will use
the ground tie to move through/under/whatever your house to the other
side. If not?

For the period of time that it takes for the charge to move AROUND the
house (not long, really, but long enough), the strike-side GROUND WILL
BE HIGH POTENTIAL to anything connected to a ground on the other side
of the house.

If there is a connection, but it is circuitous, or has an impedance to
it, and cannot carry a large surge current, the effect is reduced but
still present.

If there is not a single point entry and ground for EVERYTHING
conductive, and I mean EVERYTHING, then grounds have to be connected
across. EVERYTHING includes ANY conductor of ANY type leaving the
house, including pipe, tubing, etc, besides RF and electrical
connections.

Failure to do so and you have the likes of one story already posted to
this thread.

This equation can be complicated by parallel conductors buried next to
one another, etc, etc, but the principle remains the same.

My son-in-law mistakenly left the neutral/safety ground leads
ungrounded at an outbuilding that he ran power to. A lightning strike
A QUARTER MILE AWAY in line with the power run put all the conduit in
the building above ground (including the concrete floor), including
the frame of the drill press he was using. He woke up five minutes
later after being thrown 20 feet clear across the room.

I think I was most fortunate not to have a death in the family that
day.

Takes far less than that to smoke a piece of electronic gear.

73 and stay safe,

Guy.

----- Original Message -----
From: "Leo Starrenburg PA5LS" <[email protected]>
To: "Elecraft Reflector" <[email protected]>
Sent: Friday, March 14, 2003 5:28 PM
Subject: Re: [Elecraft] potential of static damage

>
> > What would be of
> > concern to the front end, as in ANY rig, is the induced surge from
a
> > nearby lightning strike.
>
> Hi Ron and Elecrafters,
>
> a couple of months ago we had a strike of lightning nearby, and I
had left
> the antenna connected to my K2. There was no damage other than a
"confused"
> K2: I had to do a full reset and re-program my personal settings.
>
> After this experience I rearranged the layout of the antenna feeders
to
> allow for easy disconnecting the antennas from the rigs after
operation.
>
> 73' Leo.
>
>
>
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