If your house is more then eight feet from the water line the metal
service lateral will be longer then eight feet. Since it's entire
length is installed below the frost depth it is at least likely to be a
better electrode than the two eight foot long driven rods.
Be advised that many larger diameters of underground piping can be
purchased with plastic linings and coatings. What appears to be plastic
piping may be coated steal.
"This alternating current stuff is just a fad. It is much too dangerous
Does NEC do engineering studies like this? I see #4/0 and 250MCM bonded to
ground rods and loops designed by system power engineers. Commercial or
industrial facilities may have a grounded fault of 200,000A or more so do
you really want to use #6?
Do you really want to ground such a system with just a ground rod?
Such systems usually use building steel and underground metal water
pipes as the primary grounding electrode(s). Yes, as you stated, such
systems do require the primary grounding electrode conductor to be
larger, as do _houses_ when the primary grounding electrode is an
undergound metal water pipe. However, even on those large systems, the
sole connection to a ground rod is still only required to be a #6
copper, per (2002) NEC 250.66(A). You can connect a 250 MCM to a
ground rod on such systems if you want, even Cadweld it, but it still
won't dissipate any more electrons to ground than a #6 because of the
limitations of the ground rod itself, as determined by engineering
studies. IMHO, that's why ground rods suck, while they are better than
nothing. Driving them deeper helps too.
For residential, 200 amps and below, IMO, it's easier to install bare
#4 for the entire system ground, even for ground rods, because it
avoids confusion and mostly because #4 doesn't require physical
The OP wanted to know why a _smaller_ wire was ran to the ground rod.
Sorry for not being clear.
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