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Two Grounding Rods


Mike Lamb
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Well, then how do you find them? How do you verify proper clamps?

That should be verified at the time of installation. Afterwards there's, in theory, no reason to verify it.

Ultimately, if someone wanted to verify proper grounding, he could perform resistance testing:

http://ecmweb.com/grounding/electric_gr ... echniques/

In addition to driving rods fully into the soil, I'd recommend burying the conductor to protect it from weed whackers & such.

- Jim Katen, Oregon

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Well, then how do you find them? How do you verify proper clamps?

That should be verified at the time of installation. Afterwards there's, in theory, no reason to verify it.

- Jim Katen, Oregon

Theory has its shortcomings. Ground clamps do sometimes come loose, often enough that I've boilerplate for it.

Marc

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Give the cable a gentle tug. That's what I do when I can actually see it. If the first rod is close to where the cable enters the soil, it should not give more than a couple of inches. If it feels firm I make a presumption that it's firmly clamped to its rods below grade.

Every once in a while I'll have a cable come right up out of the soil with the clamp attached or without a clamp attached. If it's a short section that just disappeared below grade it's obvious that there aren't two driven electrodes and I write it up. Sometimes the cable will come up with the clamp attached and the end will trail off below grade to the next electrode. If that continued cable feels solid I make a presumption that it's only disconnected from one electrode. I don't dig down to find the first electrode and then try to follow the cable to the second electrode. I'm not about to start rooting around next to the foundation with a spade.

ONE TEAM - ONE FIGHT!!!

Mike

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Give the cable a gentle tug. That's what I do when I can actually see it. If the first rod is close to where the cable enters the soil, it should not give more than a couple of inches. If it feels firm I make a presumption that it's firmly clamped to its rods below grade.

Please don't do that Mike. There are enough situations where current is running through the GEC, albeit at less than line voltage, where you could end up creating a shocking experience for yourself. I think if you are that curious about what might be going on a few inches below the top of the soil, you can scrape away some of the dirt.

The general safety principle here is that grounding connections of all sorts are first-to-make, last-to-break, and that on the off chance something could become energized by breaking it, you certainly don't do it barehanded.

and back to the first topic - the NEC has required this second ground rod since the 1918 edition. The wording then was actually clearer than it is today:

Where, because of dry or other high re-

sistance soils it is impracticable to obtain artificial

ground resistance as low as 25 ohms, two

such grounds 6 feet apart if practicable must

be installed, and no requirement will be made

as to resistance.

There was no scientific basis for the 25 ohm rule back then, and the only rationale for keeping the rule seems to be "well - it's been working OK to have this in the code." For contrary evidence, see the thread on CSST bonding.

Douglas Hansen

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