Hi Stan and thanks,
Gary here... I'm sure we're on the same page ... but...
I'd take exception with some of this. First it is actually the voltage that
does most of the destruction - ok - lets say 'a good deal' of the
destruction - albeit the current through an inductor is what causes that
voltage to rise very rapidly and to whatever voltage is needed to complete
the circuit and keep the current flowing ... leaving the coax on the floor -
the path that it can find IF through that is established because the voltage
goes extremely high breaking down the path and thus allowing the current to
(continue) follow that path. That stated of course high currents that are
conducted over any conductor will cause damage as well - so bottom line is
it is both voltage and current...
I'm sure we've all seen the trick of leaving the coax on the floor and
watching arcs from the center to the shield ring of the connector ...
voltage.
And one would need to take care when saying "all equipment being at the same
potential"! The real world has inductances all over the place - so there are
differences in voltage all over the place. Getting to a close approximation
is all one can hope for. Indeed if one has no damage strike after strike I'd
agree they've gotten 'close enough' for all practical purposes. But just
running wires in essence gets you to a DC ground ... not necessarily or even
probably a lightning ground.
What I want to happen is for the energy to be dissipated at the tower. If I
can keep the path from not being through the coax/control lines then an
effectively placed ground system will do just that. Connecting any wire of
reasonable size (affordable) over long distances just muddies the waters.
I just re-read an article on lightning protection in QST back in 2002 ...
and indeed it suggests if the distances are more than 100' to establish SPG
at each end and to not connect them together. Likewise it suggests longer
runs of cable/coax - being poor conductors due to their high inductance -
reduce the currents - and thus voltages - to the far end ... i.e. the shack.
Gary
K9RX
-----Original Message-----
From: Stan Labinsky Jr.
Sent: Wednesday, January 13, 2016 11:50 AM
To: StellarCAT
Subject: Re: [TowerTalk] Grounds, 'remote' towers, 'house' power system
-----Original Message-----
From: StellarCAT
Sent: Wednesday, January 13, 2016 9:28 AM
To: tower
Subject: [TowerTalk] Grounds, 'remote' towers, 'house' power system
I’m a bit confused by the push to connect my tower to the house power
coming in – direct of course ... but nonetheless connected.
Well Stellar, we tie the antenna system ground and the power ground together
so that the bulk of the strike current does NOT flow through the equipment.
If you look at the typical setup, every time you hook up the coax and plug
in the radio you have already made that connection (between the antenna
ground and power ground) but, do you really want strike current to use your
radio as a path to equalize the strike potential?
The direct connection attempts to bypass the "thru-the-rig" strike current
flow.
Add to that, ALL the radio equipment's grounding connections (the green
wire, the round pin on the power plug) should be tied to the antenna
grounding point where the antenna leads enter the building, referred to as
the Entrance Panel in some literature. Check out PolyPhaser White Papers on
the subject... eye opening!
That way ALL the radio equipment is at the SAME potential during the strike
event (picture the radio being inside of a bubble, connected to the outside
world at ONLY ONE POINT), so NO, or very little strike current flows through
your equipment.
BTW, it is strike CURRENT that kills radios! Current pulses flowing over
the ground circuits inside that thousand dollar radio will kill sensitive
components by the inductive coupling between circuit traces on the printed
circuit boards. Yea, really!
I've even heard of a situation (actually mentioned during a paid electronics
noise elimination course I was enrolled in years back) where strike current
flowing down to ground by way of the building's lightning rod's down lead
inductively coupled energy into the building's power wiring, lighting up the
whole 110/220 being fed to the office computers with shocking results. It
does happen.
Now, assuming that you lay those unhooked antenna cables on the ground
outside of your shack, well, OK. But there are reports of folks who just
laid the unhooked cables on the shack floor. Lightning came for a visit and
found whatever path to ground it could to discharge itself. The fire
department then came and cleaned up the mess.
Hope this gives you some new ideas to consider.
73 Stan
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