[TowerTalk] Ground rod sticker shock
Daron J. Wilson
daron at wilson.org
Tue Nov 9 18:02:20 EST 2004
> Copper pipe would be accepted under the code if properly
> installed. Without checking the code, off hand I would say that
> in a trench would meet the requirements.
I might argue that a copper water pipe may not be 'listed' for that
purpose, and as such might not meet the code requirements. NEC
250.52(a)(5) states that electrodes of pipe or conduit shall not be
smaller than 3/4" and where of iron or steel shall have the outer
surface galvanized or otherwise metal coated for corrosion protection,
so there is a concern regarding the size. The NEC also says (250.53(h))
that the Rod or Pipe electrode shall be driven to a depth of not less
than 8 feet, unless a rock bottom prevents that, then the rod or pipe
may be driven at an oblique angle up to 45 degrees, unless a rock bottom
prevents this. If neither of the above is possible, it may be buried
not less than 30" in a trench.
> If one is talking IEEE Std 142-1991 (the "green" book), chapter 4 goes
> a fair amount of detail about what is acceptable for grounding
> electrodes. What you are talking about with either ground rods or
> pipe is called a "made electrode" (differentiated from using something
> that's already there, such as well casings, piping, etc.). Section
> talks about Driven Electrodes. Then, there's the ever popular
> Encased Electrode (aka the Ufer ground). Finally, there's the 4.2.4
> electrodes" which refers to "buried metal strips, wires, or cables".
> depth at which the strips are buried may not be critical.... Tests by
> NBS show that resistance decreases only about 5% when burial depth is
> increased from 18 to 36 inches. Similarly, the effect of conductor
> extremely small."
Good information indeed. My point was for the price difference in a
ground rod and copper water pipe, it seems reasonable to me to just buy
the listed grounding solution and install it as recommended. Those
installs take a minute to drive the ground rod in, seems to me less
trouble then rigging up water (assuming you have pressurized water on
the site) and jetting copper water pipe in to save $2.
> Section 4.3.1 talks about choice of rods and mentions that the reason
> copper coating is NOT to make a better contact with the soil (there's
> of surface area), but to make a better contact with the (presumably)
> grounding wire.
> The code requires 8 buried feet, so the 10 foot standard rod gets you
> with 2 feet above ground to make the connection.
Made me look stuff up to learn, which is the purpose of discussion,
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