Ground Rods

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camaelec

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Article 250.56 states that if a ground rod does not test to 25 ohms or less, then one additional ground rod is to be provieded. The code does not state that additional rods are required until the resistance is less than 25 ohms. Why is only one additional rod required?
 
camaelec said:
Article 250.56 states that if a ground rod does not test to 25 ohms or less, then one additional ground rod is to be provieded. The code does not state that additional rods are required until the resistance is less than 25 ohms. Why is only one additional rod required?
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I belive tests have shown 1 more will do it.
 
Cause you've worked hard enough after having driven 2 rods. :grin:

Actually, tests have shown that the effectiveness of driven ground rods are not improved much beyond 2.
 
And to go along with the other posts, installing more ground rods regardless of the resistance is simply wasting energy and the installers time.


Roger
 
there's an equation that explains why. I learned it in school, but for the life of me can't remember it. That was about five years ago. maybe one of you guys remember it
 
I really hope you can find that equation. I don't think any of us has any clue what-so-ever as to why two are enough.

carl
 
coulter said:
I really hope you can find that equation. I don't think any of us has any clue what-so-ever as to why two are enough.

carl
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Or as already stated, why two are even necessary.

Roger
 
coulter said:
I really hope you can find that equation. I don't think any of us has any clue what-so-ever as to why two are enough.

carl
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Most cases one rod is not close to 25 ohms and adding a second rod does not
change the reading very much. The code says that the second shall not be less that 6 ft from the second rod. Actually the resistance is improved when the distance is twice the length of the rods. For a 10 ft rod the second should be spaced at 20 ft. There have been posts indicating that the inspector required that the spacing be no more that 6 ft. Why just 2 rods, the mystery remains.
 
phishwi said:
I still have all my notes and books. I'm looking for it. If I can't find it, I will get in touch with him and post it
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Phishwi, don't look to hard, the reality is, additional ground rods are simply placebos.

Roger
 
phishwi said:
In WI we are required to drive two g. rods. Has to do with soil consistency. So if we did an ohms test and failed 25 ohms, We'd end up with three rods.
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And as far as earthing is concerned, what would 25 ohms do for safety or performance?

Does WI actually have the three rod requirement as a formal amendment to the NEC?

Roger
 
phishwi said:
state. Ive never done a test, or ever heard of anyone doing one. You guys ever do one?
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Yes we do test for ground resistance for engineers specifications.

We have three point fall of potential ground resistance testers and use them only for this reason and to show Medical equipment manufactures a facilities ground resistance, but when we ask either of them why it means anything, they mumble a bunch of BS that means about as much as how bad their favorite football team did this past weekend.:D

Roger
 
Kinda the same question as why only 6 AWG to a ground rod, because lightning does not care what size it is........well as i believe roger said the attachment is not for personal safety and more so for Lightning ( and it does not care...), Transients and Line Surges so basically shoot for 25 or less and if not install a second.....90% of the installers would not buy the equipment needed to actually do the test properly and if they purchased a 3 point measuring device would probably test that incorrectly anyway....so simply add the second rod and be done and move on.......after all thats what we have helpers for.....;( oh dear....I steppin in that one.
 
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