Grounding need not be only "ground rods." For eons, the buried copper
wash boiler has been a far more effective "ground electrodes" much like
a sheet of copper buried deep enough or a mesh of bare wire. The rod is
not the only good ground electrode, just the most convenient to install,
even if not the most effective. If driven with a hammer the vibration of
the rod can cause only the lowest tip to actually by in intimate contact
with the dirt or if driven the "easy way" with a little water and
repeated up and down motion, it can have virtually no contact with the
dirt until frost and rains fill in the hole in a few years. These have
been known problems ever since the 1916 NBS report on grounding. Many
electrical inspectors reject rods driven with the water technique as not
meeting the rules for a DRIVEN ground rod. Some jurisdictions only
accept ground electrodes that are measured to have the accepted
resistance for that particular soil type. More or longer rods are often
demanded to keep the overall installation ground resistance down to some
specified value (typically 10 or 25 ohms).
Its overly restrictive to speak only of ground rods; its more general to
speak of ground electrodes which can include connections to building
steel immersed in ground contacting concrete.
73, Jerry, K0CQ
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Entire content copyright Dr. Gerald N. Johnson, electrical engineer.
Reproduction by permission only.
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