Hi Nick,
I've been reading about these Ufer grounds recently. Never heard of them
before, in fact it seems like the consensus has always been that you should
NOT ground your tower to the rebar. I can recall stories about concrete
tower foundations being cracked (almost exploding in some stories) form the
tower being attached to the rebar when a direct lightning strike hit.
Obviously, however, if it is in the NEC it must be a valid technique.
As I have a large supply of copper pipe and fittings I was thinking the
buried 7'x7' square of copper pipe around the foundation (but in the dirt...
probably treated with bentonite to improve the conductivity) would be good.
I was thinking of using type L soft copper to run from the ground "hoop" to
the tower and just connecting it to the hoop by soldering it to fittings in
the hoop. The soft copper could easily be formed to make a gentle
transition from tower to ground... no sharp bends to confuse the electrons.
I've made a variety of bus bars and other heavy conductors by flattening and
machining copper pipe of all sizes. It's easy to work with, has a fairly
good surface area if you are concerned about conducting at RF, and also has
a reasonable cross section if you are more concerned about conducting DC.
It's easy to calculate equivalent wire gauges for different pipe sizes.
I don't have an electrical inspection to be concerned with; I just want it
to work. All my inspectors will be looking at is the structural foundation.
Also, I'm blessed by being in the one area in the entire US (SF Bay area)
that has the fewest lightning strikes per year. Many (most?) guys out here
don't ground anything against lightning strikes and I've never heard on
anyone being hit. That's as opposed to my old QTH in Zero land where I have
one friend who has experienced multiple hits. In the past I've never
grounded my towers out here, but I thought I would ground this one. For one
thing, it will be 35' to 40' taller to the top of the mast than anything
I've had in the past.
However, I'm still learning about these Ufer grounds, so maybe I'll change
my mind before we pour the concrete.
Thanks & 73 - JC, K0HPS
-----Original Message-----
From: towertalk-bounces@contesting.com
[mailto:towertalk-bounces@contesting.com]On Behalf Of Nick Pair
Sent: Sunday, July 02, 2006 6:34 PM
To: towertalk@contesting.com
Subject: [TowerTalk] Grounding base slab and pier tower bases
Ufer grounds are bare solid copper wire buried in the first 3 inches of a
concrete pour with the tail brought above the surface to tie into whatever
you need to ground. The NEC (National Electrical Code) requires a minimum of
20 feet and a wire size of #2 solid bare copper. This method usually is
cheaper than copper clad ground rods or even galvanized pipes when you
consider the cost of connecting wire and approved clamps. The concrete
enhances the contact with earth and makes the best ground per area covered.
Be sure to clamp the wire to the rebar cage with a approved clamp. This is
all required by the code so be sure to do this if you are going to have any
electrical inspections. In the case of a 9' by 9' base I would run the #2
Cu 3" in from edge of perimeter of the square and 3" from the bottom of the
pour. Then take the tail up and out the top of pour for connection to tower
and tuners etc., with no splices in slab. For your base it would take about
40' for #2 solid
and one clamp. I'm sure that would be cheaper than four rods, five clamps
counting the rebar one, and interconnecting rods. Anyone considering a new
house or shack remote from house electrical grounds would benefit from this
type of ground system. Just be sure to get it in before concrete foundation
pour and have inspected before covering and you'll make your inspector very
happy.
Good luck,
Nick WB7PEK
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