At 08:52 PM 1/3/2007, ersmar@comcast.net wrote:
>Dick:
>
> Below are some nuggets of wisdom I've gathered from reading
> the postings on this reflector over the years.
>
>1. You cannot protect the tower, antennas and rigs from a direct
>lightning strike. You can only attempt to minimize the damage if
>that happens.
>
>2. Your tower ought to have at least one ground wire, minimum of
>#8 gauge wire, to one ground rod within two feet of each tower
>leg. The latest version of the National Electrical Code mandates
>two ground rods and two wires at each leg.
Really? Which code? The 2005 NEC is silent on towers, per se. Art
810.15 says masts and metal structures shall be grounded in
accordance with 810.21. 810.21 just has the stuff about the size of
the wire, straight line runs, protection of the connections, and what
can serve as a grounding electrode.
Art 820 (CATV etc) has very similar provisions.
Maybe you're thinking of some lightning protection code? Or a
recommendation of a manufacturer?
>3. You ought to ground each coax cable shield to the tower at the
>top and at the bottom of the tower.
>
>4. You ought to install lightning suppressors on all wires and
>cables coming into your shack. Polyphaser makes these as do ICE and
>Delta. <All cables> includes the coax runs, your control lines to
>your rotator and antenna switch(es), and any DC or AC supply lines
>going up the tower.
>
>5. You ought to install these suppressors immediately outside
>your shack entrance onto a single-point ground (SPG) panel. This
>panel ought to be connected to another ground rod via another #8
>minimum ground wire.
Actually, the code requires no smaller than AWG10 for copper, AWG8
for aluminum, and AWG17 for copper clad steel or bronze. (obviously,
they're more concerned about mechanical strength than resistance,
given the small size allowed for steel). 810.21(H)
More to the point, to be code compliant, you don't necessarily need
another rod, BUT, if you do, the radio system ground must be
connected to the service entrance ground by a minimum AWG6 copper or
equivalent bonding jumper. The explanatory notes following 810.21(J)
say "... bonding requirement applies only to electrodes at the same
building or structure. The use of separate radio/television
grounding electrodes is not required."
> The ground connections from all the electrical systems within
> your house (electrical supply panel, cable TV, telephone, etc.)
> should also be connected to this SPG panel.
See above comments.
By the way, code compliance (or the desirability of it) is a funny
thing. On the one hand, I'm sure lots and lots of amateurs
(including myself) have strung up many, many antennas that are not
"code compliant" and have suffered no apparent disasters from it. I
don't think I've EVER used AWG10 hard drawn copper wire for a
transmitting antenna over 150ft, even though 810.52 requires it. I
did have that AWG20 or smaller wire that I shot over a tree several
hundred feet away come down in a moderate wind, though. Such is life.
On the other hand, code compliance is a "necessary but not
sufficient" sort of thing. Just because it meets code doesn't mean
it's safe. (There is a continual tension between developer/builders
and engineers on this. The engineer specs something slightly bigger
or stronger than code, because in their judgement it's needed. The
builder says, why are you going bigger than code. It's costing me
money to do that and I'm not required to exceed the code, just meet
it. What happens next depends on the kind of job, relationship, etc.)
As others have pointed out, you could do everything perfectly to
code, take a direct hit, and still get wiped out.
>6. You ought to search the TowerTalk archives for details on how
>to do all of these things.
Heh... if you thought reading through the polyphaser catalog was an
all night proposition.. the archives for TT (while fascinating) would
be even bigger. But, still, some judicious searching will turn up a
lot of useful info.
>7. When you have finished reading all you can stand, come back
>to this reflector again and ask some more questions. We're only too
>glad to help.
>
> What did I miss mentioning, gents?
>
>73 de
>Gene Smar AD3F
Jim, W6RMK
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