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What's Wrong Here?

Sep 13, 2007 12:30 AM, By Joe Tedesco, NEC Columnist

Hint: Sand is glass now.

Donald W. Zipse, a well-known forensic engineer and engineering consultant to the electrical industry, sent in this photo that was taken inside a cottage basement out on Cape Cod, Mass. “The two ground rods had a resistance reading of approximately 600 ohms,” said Zipse. “One rod revealed a reading of 900 ohms! I could not get around the other rod to take a measurement, however, calculations for the second rod resulted in a 1800 ohm value.”

There are two things wrong with this installation.

The rods were driven into desert dry soil. Since the rods were located in the basement there was no water available to wet the soil.

Assuming the rods were 8 feet long, the two rods were electrically acting as one. To obtain the maximum grounding effect, the distance between the rods must at least be the depth of the first rod, plus the depth of the second rod. Thus, the rods should be spaced no closer than 16 feet apart. This requirement can be found in the Institute of Electrical and Electronic Engineers (IEEE) Standard 142, The Green Book.

This installation is also a tripping hazard!