Thanks to all for the answers, interesting feedback!, thanks!
Seems I will do it as actually, underground.
Cables will not be direct buried, will go through a plastic pipe, so I don´t
think that would have considerably more capacitance to ground.
Actually I´m afraid I will find some water or humidity inside the pipe and
along the cables. Will need to improve that, with a deeper channel, drainage
and a gentle slope to allow water does not stay inside the pipe.
Lighting is something to improve. A project for next year, very expensive
since I have more than 18 cables (coaxial and control lines) going to the
shack. It´s obvious that will need a Polyphaser sponsorship at CW5W :-)
Thanks!
Jorge
CX6VM/CW5W
-----Mensaje original-----
De: TowerTalk [mailto:towertalk-bounces@contesting.com] En nombre de David
Robbins
Enviado el: lunes, 09 de diciembre de 2013 10:58 a.m.
Para: towertalk@contesting.com
Asunto: Re: [TowerTalk] from towers to shack
>> Consider a direct strike to the tower? The cables being above or
>> below ground don't materially change the voltage waveform, at least
>> as selection of the suppression devices are concerned: it's kilovolts
>> you need to deal with.
>Cables "tapped" to the tower are coming off a voltage gradient from
>several
hundred KV at the top of the tower
>to zero at ground (if the tower is properly grounded). At 10 feet on a
>100
foot tower, one had several 10s of KV ..
>not easily dealt with using simple devices.
But of course ground is not 'zero' once the current traveling down the tower
gets to it, the ground potential rises also. What you need to protect
against are the signal/power carrying conductors having a different
potential than the shields of the coax or ground where the equipment is.
>> Conventional transient suppression techniques work for phone and
>> power lines, which run above ground for miles.
>Phone and power lines are not connected to lightning rods several times
>the
height of the lines.
Most distribution lines are at the TOP of the poles and get hit directly,
phone lines are usually 3/4's of the way or more up the poles... and even
more important they are not coaxial lines so the power carrying conductor is
hit which takes it directly into transformers, switches, and other
equipment.
Important Note, it is not the voltage handling capability of arresters that
matter, when the arrester turns on from a stroke it limits the voltage
across itself, that is what its purpose is! It is the current or integrated
energy handling capability of the arresting device that is important. How
you can help it is by keeping all the grounds bonded together, this keeps
the potential difference between the protected cable and the local ground
smaller which reduces the amount of current that the arrester must pass to
equalize the potential between the signal/power lead and ground.
David Robbins K1TTT
e-mail: mailto:k1ttt@arrl.net
web: http://wiki.k1ttt.net
AR-Cluster node: 145.69MHz or telnet://k1ttt.net
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