[TowerTalk] CATV & Phone grounds
jc-smith at comcast.net
Tue Jul 11 14:30:18 EDT 2006
The ground situation here has been constantly improving. When we moved in
there was one ground rod (presumably 8') tied to the electric service
entrance with #10 solid copper wire, and also to a hose bibb. The original
TV cable was grounded to some emt conduit in the garage, and the telephone
was grounded to another hose bibb. Probably typical for a house built in
When I set up my shack I added another 8' ground rod directly below the
operating position and tied that in to the 1" copper water main, which
entered the house a few feet away. A few years ago we did an underground
utility conversion and the county required another ground rod at the point
where the water main enters the house. Apparently the one I installed for
the shack wasn't close enough (about 4' away). It also had to be tied back
into the service entrance with solid copper wire, which I ran through the
attic. I don't think it was required, but since the original rod was
getting old and I didn't know how long it was in the first place I added
another 8' ground rod where my conduit came up in the garage at the service
entrance and tied it in with all the other grounds there. Or I should say I
used it as the new main ground (with #6 solid copper wire) and tied all the
other grounds to it. We now have a single cable (underground through
conduit) that handles digital phone, high speed internet and CATV, and they
grounded that to my #6 main ground wire when they installed their boxes.
The regular phone line, which arrives through another conduit, is currently
unused and not grounded.
If you are wondering how much conduit is in that trench, there is one 3" for
the 240VAC, and four 2" for telephone, cable and spares. Multiply that
times two (part of the way) because my neighbor (Gino, with the backhoe, who
helped me dig the tower foundation) and I did it together, and consider that
all that pvc pipe had to be laid side by side, not stacked, and spaced 1"
apart with sand, and you can imagine the size of trench we had to dig. Our
driveway is 100 yards long so they also required pull boxes, which we were
able to use as the split-off points for Gino's and my systems. I won't say
it was fun, but it was an interesting project.
That's the current ground situation. I'm definitely going to ground the new
tower, probably with two rods on each leg and type L soft copper tubing for
the ground "wires." How the tower ground system gets tied back into the
other grounds is still up in the air. I changed my mind about burying a
horizontal perimeter ground "rod" when I backfill around my pier for two
reasons. 1) I'll be using a special backfill mixture designed for
compacting, but not necessarily for good electrical conduction, and 2) The
tubing connecting the tower legs to the perimeter ground would be it the way
of the earth-ramming machine.
Thanks & 73 - JC, K0HPS
From: towertalk-bounces at contesting.com
[mailto:towertalk-bounces at contesting.com]On Behalf Of Red
Sent: Tuesday, July 11, 2006 9:02 AM
To: JC Smith; TowerTalk
Subject: Re: [TowerTalk] CATV & Phone grounds
I had been pondering your earlier post regarding need for a perimeter
ground or loop. PolyPhaser made an argument in their earlier book,
Grounds for Lightning Protection, for this and I observe that commercial
installations use a perimeter ground. I don't recall the reasoning.
Perhaps someone on this list can enlighten me and others.
Meanwhile, it sounds to me like your system ties utility and station
grounds together. A consideration is minimizing impedance between
them. Copper pipe should be better than wire. I think the soldered
joints are probably ample in area and they are water cooled, and both
the resistance at RF and the inductance are less than what smaller wire
would present. Is the routing of the pipe reasonably straight? Are
the tower and station grounds composed of several ground rods or other
contacts spread over an ample area? Might you improve the utility
ground by adding some rods, spaced at twice their depth? You don't want
one ground point to be poor with respect to another.
This lightning protection issue is always a probability game. You can't
reach 100% safety and you must trade-off cost of additional features vs
their added protection. Unfortunately, I can't quantify the added
protection of some of those features.
73 de Red
JC Smith wrote:
>It makes sense that all grounds be tied together, but a question is how?
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