[TowerTalk] Ground system design, RF vs AC

[Gary Schafer]

Perhaps part of the problem is understanding by some of the contributors 
as to what a single point ground system really is.

A single point ground system is a single point only as far as your radio 
and associated equipment is concerned. Meaning that all grounds and any 
other connections from the rig connect directly to one spot. This 
includes antennas, power and phone and or computer lines if involved. 
You want no other paths to your rig other than from that single ground 
connection point.

That single ground connection THEN gets tied to your ground system which 
can be several different connections to earth.

You can also have many other connections to ground outside like 
additional ground connections to your antenna lines etc.

In your case I would install a radial system just outside the wall of 
where you are mounting your protectors. Run radials out away from the 
house. Drive some ground rods in at an angle if you can.

Also run a ground wire outside the house around to where your power 
company ground is connected and connect to it with that wire. Connect 
the other end of that wire to your ground system that you have installed 
outside the house.
This will satisfy code requirements for having all ground systems tied 
together.

Run a copper strap or several heavy wires from your outside ground 
system into the protection system panel you installed just inside the wall.

You can run a power cord from a convenient outlet over to your power 
protection device to supply power. It is not important how that gets 
there. Just keep it away from the radios.

All your radio connections need to go to your protection panel. Don't 
get part of the AC power from another outlet. Only get it from that one 
on the protection panel. That will preserve your single point ground 
system. Also don't ground the radios to any other path other than to 
that protection panel.

73
Gary  k4FMX


Martin AA6E wrote:
> I appreciate the good counsel to date.  I am trying to zero in on a few
> issues.
> 
> 1.  The problem with connecting the AC green wire to the radio room
> ground and then connecting my bulkhead "SPG" to a new ground rod or
> even a perimeter ground connection is that my radio installation
> becomes part of the AC protective ground system for the house.  That
> is, any house fault or other current will partly be routed through my
> radio ground system. Is that what we want?  I believe the electrical
> code would permit the installation of an isolation transformer where
> the primary is grounded back through the house ground and the secondary
> is grounded locally.  That would be a serious expense for a possibly
> minor benefit - but it would ensure that house ground currents would
> not flow through the radio system.  I suppose it's more of an issue for
> industrial installations or recording studios...
> 
> 2.  If I install a new ground rod system near the radio room, it is
> unlikely it will be as good as the water pipe ground (about 35-40 ft
> distant) that is used by the house AC.  Especially since I can't drive
> any deep rods due to rock ledge.  How do I decide if it's better to run
> a low-inductance strap to the water pipe or to make as good a local
> connection as I can (horizontally buried cable or rod, probably)?  Of
> course, some say we should do both.  (More work!)
> 
> 3.  What's wrong with the following picture?  When we develop a local
> "single point ground" system, we are really defining a local ground
> reference plane.  If all wiring and equipment are protected by and
> bonded to this plane, why do we care if there is a good earth
> connection at all?  (It's like living in a Faraday cage, sort of.) Even
> the best ground is likely to have several ohms of DC resistance and
> maybe 50 ohms of reactance at 1 MHz.  Your random lightning bolt might
> give your system a 1 kA surge, raising your SPG to 1-10 kV relative to
> (distant) earth.  The earth ground system gives the current a
> controlled way to earth, but doesn't keep your SPG at zero volts.  As
> long as your gear is well bonded and surge protected, it may survive. 
> (Don't ask about the op!)  Thinking this way, we conclude that the
> questions about earth connections are about fire prevention & building
> safety (boring!), more than saving your equipment (important!).  Or are
> we missing something?
> 
> 73, Martin AA6E
> _______________________________________________
> 
> See: http://www.mscomputer.com  for "Self Supporting Towers", "Wireless Weather Stations", and lot's more.  Call Toll Free, 1-800-333-9041 with any questions and ask for Sherman, W2FLA.
> 
> _______________________________________________
> TowerTalk mailing list
> TowerTalk at contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
> 
>