First, happy anniversary Cam!
As to running a copper cable from the top of the tower down to ground it is
really a waste of copper. The tower itself has much lower inductance than
the wire will have so most of the current will flow in the tower along with
some in your coax lines and some in your down conductor. Even if you put an
air terminal (lightning rod) above the tower connected to the down conductor
the current will be induced into the tower and the tower will still carry
the majority of current.
Your experience is timely for the subject at hand. For all concerned, keep
in mind that all lightning strikes are not equal. Only a small number of
even direct strikes are large enough to do major damage. But there is a wide
rang of strength in lightning strikes. If nothing is done for survival such
as a little grounding and bonding it does not necessarily mean that you are
doomed to destruction. On the other hand if you do major grounding and
bonding it does not mean that your equipment is going to survive everything
but it will greatly increase the chances.
You should put jumper straps around each tower joint to make low resistance
paths around the joint. (this is a part of most good commercial grounding
and bonding)I assume that the arcing was at leg joints which is common
during a large strike.
This is exactly what can happen in the bearings of the rotator if you do not
put a strap around it from the mast to the tower. The bearings do not make a
good low resistance connection just as a tower leg joint does not make a
good low resistance connection. This can be verified with a milliohmeter in
either case.
Or you can do nothing and hope for the best as some suggest.
Anyone ever notice how many position pots are bad in the Ham M and t2X
series rotators? I have a half dozen of them at the time with at least half
of them with bad pots. Not sure if it is caused by lightning but I can see
where it could easily be as the center arm of the pot is electrically
connected to the upper housing of the rotator. A moderate lightning strike
with the rotator not bypassed and the rotator case gets elevated in voltage
and part of it can go right thru the pot.
73
Gary K4FMX
> -----Original Message-----
> From: towertalk-bounces@contesting.com [mailto:towertalk-
> bounces@contesting.com] On Behalf Of Cam and Juli Hedrick
> Sent: Thursday, December 14, 2006 5:13 PM
> To: towertalk@contesting.com
> Subject: Re: [TowerTalk] Lightning Damage to Rotor Housings.
>
>
> OK Gang, here's my experience:
> I lost a TX2, thrust bearing, mast, and Telrex 20m 6 element Monobander to
> a
> direct hit last year. I have commercial level ground grid beneath my
> towers
> and have sustained lightning strikes before. This of course was a direct
> strike and the others obviously weren't. I had the tower itself inspected
> for damage and replaced two sections due to arcing that had occurred.
> Now,
> all of my towers have a 00 cable running from the top down to the grid. I
> figure copper will take the hit before the tower next time.
>
> Now I'm off to my anniversary dinner with the Love of My Life.
>
> Cam Hedrick
> WA4JKW
>
>
>
> _______________________________________________
>
>
>
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