[TowerTalk] lightning protection

[Pete Smith]

At 08:21 AM 3/2/2009, Paul Kelley N1BUG wrote:
>....
>Most hams here rely on disconnecting cables for lightning
>protection. I am no exception, but last June I had a very convincing
>demonstration of the fact that disconnecting things offers no
>protection from a direct strike. EVERY cable from the towers was
>disconnected in my basement, with at least three feet of dry air
>between the ends of those cables and the mating ends of cables
>running up to the ham shack. In the shack ALL power, phone, and data
>cables were unplugged with at least two feet between receptacles and
>cords. One of my towers took a (small?) direct hit. Following the
>deafening snap and blinding flash throughout my home, I spent an
>hour nervously picking up fragmented remains of ham gear that had
>been blown apart. I've spent much of the last nine months rebuilding
>and repairing what could be salvaged. I'll spend the next several
>years recovering financially. The ham gear was at "ground zero" but
>I lost most of my household electronics and appliances too.

On the other hand, if you are like most of us, there really is no good 
alternative to unplugging everything going to the tower.  You can spend 
thousands of dollars on Polyphaser hardware, but unless your shack is 
absolutely properly engineered, you will still have damage from a strike, 
perhaps far worse than with disconnection.

My shack is on the second floor - my ground leads have significant 
inductance at the frequencies relevant to a lightning hit.  It's an old 
house, with some real question-marks as to how the electrical wiring was 
done.  I chose to disconnect everything at the entry panel, in one of the 
double-hung windows, rather than attempt to re-do so much.

Three years ago in August my tower, about 200 feet from the house, took a 
major direct hit.  Everything on the tower (two rotators, an antenna 
switchbox and a stackmatch) was fried.  None of my ham equipment was harmed 
in any way.  My wife's and my computers were damaged, probably due to 
induced voltage on our wired ethernet network.  Our telephone answering 
machine was damaged ... and that was it.

I infer from this that the damage we had, except on the tower, was due to 
induced voltages on various conductors, resulting from the nearby strike, 
rather than directly conducted strike energy.  A whole-house surge 
protector attenuated the energy on the house's above-ground AC service, and 
a gas-tube protector did the same on the above-ground cable 
service.  Except for the answering machine, the telco's gas-tube protector 
saved our phones.

The best part was that our homeowner's insurance paid for replacement cost 
of everything that was damaged.

73, Pete N4ZR