Lightning events happen in a VERY short time
As I understand it, the conductors that you are using in your
lightning protection system to BOND all the chassis together
and thence to your entrance panel, and thence to your
grounding system (rods, horizontal connectors, et al) need to
be LOW INDUCTANCE.
IF I still grasp what Jim, et al. have been
trying to teach us about lightning protection vs. RFI
The GOAL is to keep our stations at the same
ground potential as where we want the lightning energy to
GO.... Because the lightning event IS going to enter your
shack if the event occurs close enough to ANYTHING connected
Thus, the GOAL is to keep the energy from the lightning event
on the grounding conductors and on the outside of the devices
(chassis) long enough for the energy to seek a "safe"er path
Inductance and resistance.... BOTH need to
be minimal in the path to earth ground so that the lightning
event can pass through the system without creating too high of
a ground potential difference anywhere and arcing/jumping from
a "safe" place to a "dangerous"/damaging place.
Resistance can be reduced by shortening a
conductor or merely making it BIGGER.... This reduces the
"resistance" to change in voltage in the event...
INDUCTANCE opposes the increase in CURRENT through the
conductor.... And as I understand it, inductance is reduced
in a conductor by INCREASING the surface area of a
conductor.... and the most reasonable way of doing THAT is by
using wide, thinner conductors like straps.... typically
COPPER straps as copper is the best compromise between lower
cost and higher conductivity.
Thus, in summary.... the conductors you are
using to bond everything together would IDEALLY be the widest
copper strap you can route from place to place....
Strap/sheet copper is notoriously hard to route around
corners, et al.... and this is ACTUALLY a good thing, because
lightning does NOT like to turn corners.... The strap/sheet
should be routed as close to a straight path as possible....
Where you MUST make direction changes, they should be as
gradual as possible... AND IF you must make a 90 degree
change indirection over a short radius, you should consider
engineering to do so with additional methods of reducing
inductance in other ways. (soldering/brazing folds, et al).
I know this isn't totally correct and
complete, but I think it's pretty close.
Clay Autery, KY5G
On 05/10/20 09:46, KE1F Lou wrote:
How would you measure that impedance? Between which two points?
On 5/10/2020 9:19 AM, john ni0k wrote:
Have you measured the impedance of your ground connection? If
the impedance isn't very low all the surge suppressors won't
help you. Telcos and cell sites will do this and add to the
ground system until it gets below 20 ohms. In some cases much
lower than this.
-de John NIØK
John Canfield wrote on 5/10/2020 8:08 AM:
I faithfully followed the grounding and bonding
recommendations in the ARRL book. My entrance panel is by
KF7P, every conductor (even the SteppIR 16
conductor control cable) that enters the shack is
surge suppressed - both at the tower base and the shack
entrance. The copper plate in the box is bonded to a ground
rod which goes to another ground rod a few feet away and
then on to the main AC load center ground rod and then up to
the ground buss in that box. In the KF7P entrance box, a
copper strap goes to a common ground buss in the shack.
Every piece of equipment in the shack is connected directly
to the common ground buss via braided wire.
My tower is 165' feet from the shack so there was no reason
to bond the tower to the entrance panel. All coax is in one
3" conduit and all other wiring is in another 3" conduit.
I've put a lot of research and effort (and $$$) into
lightning mitigation and I'm very happy with the results so
far. We've taken some very close lightning strikes in the
last few months.
Thanks to all for your tips and recommendations es 73 de