----- Original Message -----
From: "Bill Austin" <billaustin@powernet.net>
To: <towertalk@contesting.com>
Sent: Saturday, March 20, 2004 12:01 AM
Subject: [TowerTalk] New Tower Grounding Advice
> I'm putting up a new 60ft self-supporting Trylon. I'm wondering how
> much and what type of grounding needs to be done. Any advice and
> suggestions would be greatly appreciated.
Check out the Erico, Polyphaser, and ICE sites.. they've got lots of info...
>
> I bought three grounding kits with the tower, one for each leg. I plan
> to tie the three rods together using some #4 solid copper. I plan to
> tie the electrical grounds for each of the three buildings near the
> tower into this loop. Each building has it's own breaker box and ground
> rod, and all three connect back to the same distribution panel.
Go to the library and check the NEC for how the power distribution grounding
MUST be done. There's specific requirements for the design of the grounding
system and for the size of grounding conductors, etc. For instance, are the
subpanels in the buildings fed with underground conduit/raceway or overhead
lines?
Don't try to make your electrical power ground serve as the lighting ground
or the RF ground. Three needs, three ground systems, three sets of
requirements. In short:
1) Power ground - serves to keep cases of equipment at a safe potential when
an internal fault occurs. Has to be low enough impedance at 60Hz to make
the breaker trip in the case of a short to case.
2) Lightning ground - served to conduct very high peak currents with fast
edges into the ground, without inducing voltages or currents in surrounding
stuff. Inductance is critical (because lightning has high di/dt). Also,
you want to minimize "step" potential (that is, the voltage between two
points on the surface of the soil a few feet apart). Power dissipation
capability is also important (which is a balance between resistance and
thermal capacity... mostly, you're depending on the soil to be the "load")
3) RF ground - this is for your antennas, etc., and needs to be an
appropriate impedance at your operating frequency. You want the RF ground
to be separated enough from #1 and #2 that voltages induced in those ground
systems don't wind up in your radio gear.
I also
> have a lightning rod to go on top the tower, and plan to run a separate
> copper wire down the tower to the grounding loop at the bottom.
The tower IS a lightning rod.
>
> I've been reading the archives for some time now. I was looking at
> Roger Halstead's site (linked in a recent post) and all the work he did
> with his towers. I was just wondering what else I should plan on doing.
> We have the rebar in, and I hope to be pouring concrete next Friday.
Consider putting the appropriate amount of bare copper wire into the
concrete to make a UFER ground. Concrete, in the soil, is a fairly good
conductor, and has a huge contact area (more than any dozen or so ground
rods you might laboriously hammer into the ground would have).
>
> Thanks & 73,
> Bill - KD7ZAH
>
>
> _______________________________________________
>
> 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.
>
> _______________________________________________
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> http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
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.
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