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.
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.
73,
... Joe, W4TV
On 12/8/2013 11:59 PM, Jim Lux wrote:
On 12/8/13 8:46 PM, Joe Subich, W4TV wrote:
I think as a practical matter, whatever transient suppression you do
at the entrance to the shack is going to be the same whether the
cables are laying on the ground, suspended 10 feet off the ground,
or buried a couple feet deep.
Not if the cables are coming off the tower 10 - 15' high unless one
has a grounded metallic "cable bridge" above the cables and connects
the cable shields to the bridge/tower where they leave the tower.
With cables exiting the tower some distance above ground, the lightning
protection at the shack entrance will be much more critical.
But what would you do differently, transient protection wise?
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.
A strike right to the cables? Is that particularly likely, given that
there's a tall tower and a not as tall house next to it?
Conventional transient suppression techniques work for phone and power
lines, which run above ground for miles.
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