I've been following this thread for a while and wonder why no one has
mentioned that a 'ground bar' is NOT a single-point ground.
Think of the 'ground bar' as a series-string of very low value RESISTORS.
Now ... think of your equipment as being connected to the 'nodes'
between each of those resistors ... rig A at one end, then rig B at
the first 'node' ... rig C at the second 'node' ... etc.
During a lightning strike, the huge voltage of the strike MIGHT appear
across that 'string' of resistors, causing each 'rig' to be at a
DIFFERENT potential.
POOF !!
I suggest that each piece of equipment have its own 'ground wire' and
those all be connected to a SINGLE point, perhaps at a point closest
to the ground rod. (Mine are all connected to a #0 wire going through
the wall to the ground rod about 7' from the 'single point'.
Good luck.
Don
N8DE
Quoting Jim Lux <jimlux@earthlink.net>:
On 3/20/14 10:34 PM, Jim Brown wrote:
All of the replies I've seen here are obsessing on the wrong topic. By
all means DO take care to avoid oxidation and dissimilar metals
problems. But that ground bar, whatever it is, is NOT an important
element of what you're doing, which is primarily LIGHTNING SUPPRESSION,
but also minimizing hum, buzz, and RFI.
What matters is that EVERY CHASSIS in your shack be bonded together by
short fat copper, and that combination of chassis bonded to everything
in your house by short fat copper.
I agree on bonding, but not on fat. At RF frequencies, the inductance
(1 uH/meter) will dominate over the AC resistance. At 1 MHz
(lightning frequencies) 1 meter of AWG 16 copper wire has a AC
resistance of about 0.07 ohms. It has an inductive impedance of 6.3
ohms.
That includes antenna entry, every
ground rod, the power system ground, the telco ground, the CATV ground,
the satellite ground, structrural steel ground (if any), and, if your
tower is close to the house, the tower ground.
You are also forgetting that bonding between equipment should also be
short, fat copper. When you run wires from each piece of gear to a bar
at the back of he desk, that usually makes the connection more than
twice as long. That means double the resistance and double the
inductance. NOT a good thing.
The BEST bonding method in the shack is short, fat copper from chassis
to chassis of every piece of gear in the shack, then a bond from one of
those chassis (preferably the rig) to those other grounds in your home.
Chassis to chassis bonding minimizes hum, buzz, and RFI. Bonding all the
grounds together and to earth provides lightning safety.
I'd rather have someone use smaller easier to manipulate wire that is
short, than big fat stiff bars or wires that wind up being long.
And, of course, avoiding loops which can intercept the magnetic field
from a transient flowing in another conductor.
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