On Wed, 26 Jan 2005 15:48:51 -0500, Tom Rauch wrote:
>Anyone know what the resistivity per unit volume concrete
>is?
In doing research for my white paper on power and grounding, I
learned that you can buy different types of concrete designed for
either very high or very low resistivities, depending on your
application. There are, for example, mixes for use as ties on
electric transit systems that have extremely high resistivity, and
mixes designed for use in Ufers that have very low resistivity. And
there's everything in between.
When I posed a question on the RFI list re: concrete and grounding,
Dale, WA9ENA, who is an EMC engineer at Rockwell-Collins, responded
with his research/study from sources (including AT&T) that concrete
that becomes part of the path of a lightning hit CAN, indeed,
explode.
I think the bottom line is that any concrete that could become part
of the path of a hit be engineered so that it is a relatively high
resistance part of that path, and that any Ufers (intentional, low-Z
ground elements) NOT be part of a structural system.
Jim Brown K9YC
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