I think all you guys have the concept down correctly, but this term
"single point ground" has always been a major point of confusion. It is
a terrible misnomer. I actually refuse to use it. Instead I substitute
the term "common ground tie point". When the SPG term is used, many who
are just learning or are unclear on the requirements think the term is
self explanatory and there can be only one ground in the system and that
is where their thinking starts to go astray. They then think you cannot
have two separate ground tie points either. They usually don't actually
consider the extreme of that concept which is, you cannot have an SPG at
all because someone else already has it. I was once called in to debug a
problem on a piece of electronic hardware, and when I got to looking at
it, the designer had run all the many grounds off each of the PC cards
and had taken them all back over 3 feet of wire and tied them all
together at one common point. What a disaster that was. Another case of
someone thinking that an SPG means only ONE ground.
I wish I could wipe the term completely, but it is firmly engrained in
our literature.
Jerry, K4SAV
Jim Brown wrote:
>On Fri, 05 Jan 2007 12:13:37 -0500, Les Kalmus wrote:
>
>
>
>>Should be OK, no?
>>
>>
>
>Not ideal. The BEST, by far, is for all cables -- power, antennas,
>CATV, telco to enter at the same point so that the ground
>connections between them can be as short as possible.
>
>Remember that the MOST important element of lightning protection
>is for all of those systems to be at the same potential when a
>strike hits. The wires connecting the grounds will carry current,
>and there will be both induced voltage and IZ drop across their
>inductance. So in the world of lightning protection, SHORT is
>important.
>
>Gary Schafer, K4FMX, said:
>
>
>
>>A single point ground is NOT a place or spot in the earth but it
>>is a point of common connection which can be anywhere designated.
>>
>>
>
>Yes.
>
>
>
>>The whole idea of a single point ground is to have a place to tie
>>all lines together with zero impedance between them. You can run
>>as many grounds to earth from that point as you desire. But all
>>cables entering the shack must be physically mounted to that
>>single point ground panel.
>>
>>
>
>AND THAT PANEL MUST HAVE A SHORT BOND TO ALL OF THE OTHER GROUND
>BONDS IN YOUR BUILDING -- POWER, CATV, COLD WATER, BUILDING STEEL,
>AND LIGHTING PROTECTION. Caps added for emphasis. This is quite
>important.
>
>As hams, we tend to focus on our INTENTIONAL antennas, but they
>are only one element of the problem. Lightning will see every
>other conductor in our home as an antenna, and will induce current
>onto each of them based on their length, orientation, and where
>they are connected. The telephone line is a very good receiving
>antenna for lightning. So is the power line. So is the downlead
>from a cable TV system. We ignore them at our peril.
>
>Several of my friends in the pro audio world who have no
>INTENTIONAL radio antennas at all have lost all of the Ethernet
>and printer interfaces in their home office computer systems from
>lightning.
>
>73,
>
>Jim Brown K9YC
>
>
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