If you get really uptight about your connections consider this... The
proscription against welding the rebar is a rebar strength issue. Just
extend the rebar a bit past its "standard planned length" and weld to
the extension which is not involved in the design of the cage. I have
welded stainless steel tabs to steel with ease. Then I could use SS
bolts to secure copper ground strap and not get the corrosion I would
expect with plain steel. The forgoing will work but as Jim L says, it
may not make much of an improvement.
When in doubt I typically opt for the more is better approach.
Patrick NJ5G
On 5/3/2014 8:44 AM, Jim Lux wrote:
On 5/2/14, 6:04 PM, N3AE wrote:
I've been following this thread with interest.
What's the proper way to bond galvanized steel anchor rods to the
rebar cage to get a good Ufer ground? The UST specs specifically
state not to weld the rebar (because they call out ASTM A-615 rebar,
not the weldable A-706).
tie it.
A variety of testing has shown that the metal conductors in a concrete
encased grounding electrode do not have to be continuous. There was
one paper where they tested versions of Ufer grounds where the
segments of rebar that were welded, segments that were tied, and
segments that were just laid together. They all worked acceptably.
I'm sure there are pathological cases: if you had a bunch of 6" long
pieces of rebar randomly placed in a big block of concrete) that
technically meet the 20 feet of conductor guideline; but, I would
think that pretty much any "conventional" assembly technique would work.
It's mostly about providing a suitable large area contact with the
surrounding soil, and after that, making the current density in the
metal and at the metal to concrete interface low enough.
My plan is to use bronze rebar ground clamps rated for direct burial
for both the wire-tied rebar cage and the anchor rod connections,
with #4 AWG solid copper wire between them and a bit of stainless
shim stock between the clamps and the galvanized anchor rods (for the
dissimilar metals problem - galvanized with copper-bronze clamps).
All the above encapsulated in the concrete pour.
Make sense? Are the SS shims overkill or even undesirable (compromise
the tightness of the connection to the anchor rods)?
Shawn - N3AE
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