On 7/16/13 5:45 PM, les wrote:
I am putting up a new tower and was wondering if the ground rod for it
can go through the concrete in the base or is it better to place it
outside the concrete base?
_
you don't really need a "rod" into the base to make a good ground. A
"concrete encased grounding electrode" (also known as a Ufer ground,
after Herb Ufer, who invented them) has a lower resistance to "ground"
than almost anything else you might come up with.
To make a CEGR/Ufer what you do is either "bond" to the rebar cage or
put 20 feet of suitable bare copper wire (AWG 4 or bigger) into the
concrete arranged so it's reasonably spread out (e.g. burying a coil of
copper wire doesn't do much good).
Bonding to the rebar works if
a) the rebar isn't the kind covered with an insulating coating
b) you have a good way to bond to it
c) the rebar is tied together reasonably tightly.
Some ways that folks get the bond is by bringing a piece of the rebar up
through the top of the concrete, and then using a suitable clamp to
that. (that makes a bit of a challenge.. the clamp is then something you
need to maintain).
THe other way is to run a copper wire down into the concrete and clamp
it to the rebar. Again there's the whole "suitable clamp" thing,
although once encased in concrete, it's not like the bolts will come loose.
So that's why the most common Ufer ground is the 20 feet of AWG 4 in the
concrete (wrapped around the rebar cage for instance.
What is *really really* important is that NOTHING should penetrate the
concrete/soil interface. No rebar sticking out of the side of the
concrete below grade. No copper wires sticking out to bond to ground
rods. No rods sticking out the bottom of the concrete. Only concrete
should be touching soil.
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