While it may work for some, I'm not a big fan of the disconnect method. It
relies on the assumption that you will always disconnect *every* possible
path into the house. Those who disconnect all cables after every on-the-air
session might succeed at this, but many will forget to do it or will not be
home when the dreaded lightning storm approaches. If you forget just one
wire your entire house will be exposed to the danger. In other words, you
must disconnect every conductor *outside* the house. Yeah, you might save
the rig by putting it in the middle of the room, but a bolt of lightning can
jump an amazing distance from the end of a piece of coax laying on the
floor. The idea is to protect the house and everything in it. Secondarily,
you might want to protect those long runs of expensive hardline and rotor
cable, too.
Sometimes the disconnect method is simply not practical. If you've ever seen
the rat's nest of cables and wires at a major multi-multi, you know what I
mean. And those guys have the tallest towers with the most exposure to the
danger! The more complicated the station, the less feasible it is to
guarantee that everything will be disconnected at the proper time.
Also note that a lot of damage can be done by EMP from a moderately distant
electrical storm. Your tower doesn't have to take a direct hit for this to
happen. Surge induction can wipe you out as well. If you follow the
disconnect philosophy, this means you have to be even more vigilant and
aware of any electrical storms in your region. Many of us have found
ourselves needing to continue operating in a contest when an electrical
storm was in the area, but not close enough for there to be any danger of a
direct hit. You can't do that safely if you don't have surge protection on
every conductor in the station.
BC stations have always had to deal with this problem. It's not at all
practical for them to disconnect, yet they have an outstanding track record
of being able to stay on the air even when lightning storms are in their
vicinity. The technology exists, if you are prepared to do it right.
This means that if you are going to go the protection route, you have to
follow the rules: lots of ground rods, low impedance paths to ground,
reliable connections (Cadweld preferred for ground rods), entry bulkhead,
suppressors at both ends of every conductor that enters the shack (telco,
too), binding all grounds (telco, AC, station, bulkhead, tower) to a single
point ground, etc. It's not cheap: probably $1,000+ for the average SO2R
station.
73, Dick WC1M
> -----Original Message-----
> From: Pete Smith [mailto:n4zr@contesting.com]
> Sent: Wednesday, May 21, 2003 5:42 AM
> To: Wes Attaway (N5WA); ww5l@gte.net; Kelly Taylor
> Cc: towertalk@contesting.com
> Subject: RE: [TowerTalk] grounding
>
>
> At 09:30 PM 5/20/03 -0500, Wes Attaway \(N5WA\) wrote:
> >Going from a second floor room to ground for the
> >purpose of a so-called DC ground is not much of a problem.
> Your coax
> >should be grounded near the ground out at the tower, and maybe again
> >just outside the house before coming up to the second floor,
> so I don't
> >think it would much of an issue as far as the second floor goes. DC
> >grounding and RF grounding problems are two different animals.
>
> But lightning is much more like RF than DC, according to the
> Polyphaser
> book, because of the short rise-time. That's why they put so
> much emphasis
> on the use of short, wide, straight (low-inductance) copper strap for
> grounding their SPG bulkheads. I understand that
> hypothetically you could
> have a situation where a strike caused all the grounds in a
> station to rise
> to the same (relatively high) potential, and because there was no
> difference between them no damage would occur. But frankly,
> I'm not that
> confident of my ability to make that occur.
>
> It seems to me that all this is a matter of probabilities.
> Since I don't
> need 24/7 operational capability, I would rather disconnect
> all conductors
> going to my tower, in the belief that any direct strike or
> serious induced
> voltages are much more likely to arrive in my shack by this
> route. My AC
> service has a whole-house surge protector, all items in the
> station are on
> surge-protector strips, and my telephone line also passes
> through a surge
> protector. I'm sure there are still scenarios where I could sustain
> damage, but I think the likelihood is acceptably low.
>
> 73, Pete N4ZR
> The World HF Contest Station Database was updated 9 May 03.
> Are you current? www.pvrc.org/wcsd/wcsdsearch.htm
>
>
>
>
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