[TenTec] Station Grounding

[Dr. Gerald N. Johnson]

On Fri, 2007-01-26 at 20:26 -0500, Carl Moreschi wrote:
> The whole question here about grounding is really one of expense.  Clearly
> the best setup is to ground everything together from the tower to the shack
> with 0 gauge or larger wire.

18" wide copper strap is better, lower inductance.

> All bonds must present virtually 0 resistance.
> Even .001 ohms is too high with a direct lightning strike.  Commercial
> stations spend hundreds of thousands of dollars doing this and they do it
> well.

With a band of 18" wide copper strap around the building or at least the
room to be protected and with all ins and out going through Polyphasors
mounted IN the copper strap. Power and RF.
> 
> On the other hand, for an amateur station on a reasonable budget, grounding
> to the necessary level becomes expensive and possibly impractical.  The next
> best solution is to disconnect everything.
> 
> The first 5 years I lived at my Franklinton QTH, I lost from $1000 to $2000
> a year in electronic equipment from nearby lightning strikes.  I had the
> best grounding I could make, and all kinds of MOV lightning protectors
> including a whole house 3 legged protector at the power line entrance.  In
> fact my home owners insurance threatened to cancel me.  I then went to a 100%
> disconnect setup.  This meant that all my electronic equipment was
> disconnected from power lines, phone line, rotor control, everything.  I
> brought all these lines into my home through a a metal plate and
> disconnected everything at the plate.  Well, I lived there for another 15
> years and never, I repeat never had another problem from lightning.

When there's the voltage drop from a few kiloamps of lightning going
down the tower ground, it only takes a foot or two of gap to keep that
remaining voltage away from the electronic. But a smaller gap has cost
me equipment.

Then a few hundred amps going down a connected coax only made for and
amp or two tends to make gaps or to induce enough current to take out
radios by burning off the PC board traces (long after the semiconductors
have melted).

Good lightning protection is like making a good filter. You get a slow
roll off on a filter with a single reactive component. You get twice the
rate of roll off with two reactive components, one series and one shunt.
You keep out lightning some with one component, all the grounds you can
muster connected by the largest possible copper. That cuts the voltage
from megavolts to kilovolts. Say you have a big hit, 10 kiloamps. The
ground system may have 10 ohms, might have 40 ohms resistance. If 10
ohms, that still allows a voltage rise of 100KV. And it doesn't take
nearly the gap to hold of 100 KV than the lightning has already broken
down from cloud to ground. I think the station equipment should have all
its grounds tied together too, but only connected to the tower ground
when RF burns demand it during operation.

The codes are set all for grounding because that's easier to understand
and to inspect than to allow for other methods that may be superior. And
the codes have been that way for a century.
> 
> Carl Moreschi N4PY
> 121 Little Bell Drive
> Bell Mountain
> Hays, NC 28635

-- 
73, Jerry, K0CQ,
All content copyright Dr. Gerald N. Johnson, electrical engineer