Bonding everything (all grounds) to the main A.C. grounding electrode in
accordance with the National Electrical Code avoids voltage differential
during strike events. (at least that seems to be my experience with
commercial repeater installations with antennas at 197 feet or higher)
73 ES DX,
Gary - AB9M
On 1/13/2016 12:30 PM, Gary Schafer wrote:
Lightning can be thought of as a constant current source. A strike will
contain X amount of amps and it will conduct that amount of current to
earth. If there is resistance/inductance in the path, the voltage will rise
to whatever is needed to maintain the X amount of current.
So yes, leaving ungrounded coax cables laying on the floor is a bad idea.
The voltage will rise until it is high enough to create an arc to a path to
earth to dissipate the charge.
You most always should have two ground systems unless your tower is right at
the shack entrance.
The tower should have its ground system at the tower base, ground rods
radials etc.
Then you need a similar ground system at the shack entrance where your
single point shack ground system gets grounded. This needs ground rods,
radials etc.
You should always tie both ground systems together and to the power ground
for safety. The ground lead between tower and shack will dissipate some of
the lightning energy and help equalize voltages in the area but it should
not be a substitute for a ground system at either end.
Both ground systems are important as you want to discharge as much energy to
earth right at the tower as possible if the tower is struck or energy is
induced into it.
The ground system at the shack will take up a lot of what is left over that
the tower ground system did not take care of and it will dissipate a large
part of energy if a strike comes in on the power line or phone/TV etc.
lines.
Having all the equipment, power, coax etc tied together at the single point
ground panel keeps the potential the same on all lines as they enter the
shack. The fact that the single point panel has a ground lead a few feet
long to its ground system will allow some voltage rise there but all lines
to the equipment will have near equal voltage.
If the power comes into the shack from a ways away of the other side of the
house a good thing to do is run an ac line (from an outlet in the shack)
over to the single point ground panel where AC protectors are placed on that
line and then power all of your equipment only from that AC outlet on the
single point ground panel. That will place the AC power at the same level as
the coax lines.
73
Gary K4FMX
-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of
StellarCAT
Sent: Wednesday, January 13, 2016 11:16 AM
To: tower
Subject: Re: [TowerTalk] Grounds, 'remote' towers, 'house' power system
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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