Hi Paul-
I thought that one is NOT supposed to ever weld to the rebar, unless the
rebar is spec'd for welding, which most are not; that all grounding wire
should be clamped to the rebar and then when the wire leaves the area of
the tower base, you should/could cad weld it to the ground rod system.
Am I wrong here? (I'm about to build a concrete tower base with a 5' x
5' x 8' deep hole and a lot of rebar).
Dick, K0CAT
============================
Paul Christensen wrote on 7/14/2016 10:48 PM:
It's looking more probable that the remote Internet site built last year by
N4CC and myself will require a complete move about a half-mile down the
road. Assuming this is the case, I want to pay particular attention this
time to Ufer grounding of the two tower bases. These are large Pirod
self-supporting towers with substantial concrete piers. The relevant
portion of Motorola's R56 standard is copied and pasted below. The soil in
this area is very sandy and at the current site, we ended up having to drive
down a total of four 24 ft. rods to get adequately low earthing resistance.
That was a rough day of work even with a hammer drill.
My thought is to "spiral wind" solid #2 AWG wire, beginning the bottom rebar
layer. Cadweld it at the start point, and then periodically Cadweld at
random points where the wire crosses other rebar sections. The wire would
exit at the top of the pier using a small-diameter PVC pipe as shown in one
of the R56 diagrams. As the wire nears the top, possibly it could branch
out into two additional directions for bonding to the tower base and
perimeter ring.
Any issues with this plan?
Paul, W9AC
Motorola R56 Ufer Guidelines:
. Concrete-encased electrodes shall be encased by at least 51 mm (2 in.) of
concrete, located within
and near the bottom of a concrete foundation or footing that is in direct
contact with the earth.
. Concrete-encased electrodes shall be at least 6.1 m (20 ft.) of bare
copper conductor not smaller
than 25 mm2 csa (#4 AWG) or at least 6.1 m (20 ft.) of one or more bare or
zinc galvanized or other
conductive coated steel reinforcing bars or rods at least 12.7 mm (0.5 in.)
in diameter.
. Concrete-encased electrodes shall be bonded to any other grounding
electrode system at the site.
See "Common Grounding (Earthing)" on page 4-5.
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