The only thing about lightening is it is unpredictable.
Lightening introduces voltage into your rigs through two methods;
Conduction and induction. I think most of us have seen the statement
that a typical lightening strike a mile away can induce as much a one
thousand volts per meter of conductor.
A strike to your tower is one whale of a lot closer, So, it can induce a
lot more than a thousand volts per meter into your house wiring. That's
electrical wiring, telephone wiring, Internet wiring, interconnecting
wires between equipment. IOW any conductors.
A strike to the tower will follow ALL conductors from the tower. The
pulse is divided between all grounding that is connected to the tower.
NORMALLY a good grounding network will reduce conducted voltages as you
move away from the tower. Coax with the shield grounded at the base of
the tower, benefits from this same grounding network.
If the rig is also connected to that grounding "system" there will be
some fraction of the original pulse that went into the ground. At the
same time, you have induced voltage in ALL house wiring that is
connected to the rig(s). This is NOT DC voltages, but rather a "ringing
AC voltage that peaks somewhere around 1 KHz.
Because of the different routes the voltage takes, the peaks are
unlikely to reach the rigs at the same time, meaning the voltage
differences may be very large. A common point ground for all wiring
located near the rigs can be helpful and certainly is a good idea (It is
recommended), but still offers no 100% guarantee.
It must be emphasized that NO grounding system offers 100% protection
because you have some finite voltage left after all the grounding that
depends on the strength of the strike, the conductivity of the earth in
which the grounding rods are driven along with the number of ground
rods. NORMALLY as you add to a well designed ground system, the better
the protection. BUT you quickly run into diminishing returns where it
costs a lot to get even a little more protection
"The best protection", although not usually practical is to disconnect
all wires into the rigs and at the inside of the common point ground
which leaves all lines coming in, grounded at that point.
NEVER disconnect the coax at the rig(s) and leave it/them laying on the
floor. That's worse than Ben Francklin's experiment and very dangerous.
They need to be waterproofed and thrown outside.
Hmmm Typed this the middle of the afternoon. Brought the monitor up and
it's still here.
73
Roger (K8RI)
On 7/20/2015 1:41 PM, Kent Olsen wrote:
Hi all
I have seen the video on the kf7p.com website about his great looking coax
entrance panels that I am planning on buying for my tower.
https://www.youtube.com/watch?v=in8x8juZTj8
Last night we had a thunder storm go over head and it got me thinking. In
the video Chris explains about the different connections. The connections I
will be referring to are the copper strap from the tower which is grounded
through some ground rods and the copper braid from your equipment to the
box. Last night I disconnected my coax from my radio and waited for the
storm to pass. If I were to connect the braid to my equipment and my tower
were struck by lightning would the energy from the strike go through the
strap to the box through the braid into my equipment in the shack causing
damage? Would the ground rod or rods dissipate enough energy to save the
equipment?
Thanks
73
Kent
NC6B
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73
Roger (K8RI)
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