ground rod


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Old 12-13-15, 12:36 PM
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ground rod

An electrician added an additional ground rod to my house to bring it up to code. After several failed attempts to drive it straight down (hitting ledge at 4")he gave up and drove the rod at a shallow angle. My guess is that the rod is only 1-2 feet deep. Is this acceptable?
 
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Old 12-13-15, 01:00 PM
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No and he should have known better then that.
How far out from the foundation was he trying to drive it.
He may have hit the footing it he was not out far enough.
 
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Old 12-13-15, 01:31 PM
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You can drive ground rods at 45 or dig a trench and bury them horizontally.
 
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Old 12-13-15, 06:51 PM
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He was not hitting the footers. It's NH and he was hitting granite. I thought going in at an angle was a better idea than my suggestion of just cutting the rod off at 4'.

Not that I'm planning on moving anything, but how deep would the trench have to be?
 
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Old 12-13-15, 07:36 PM
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NEC Article 250:
3. The electrode shall be installed such that at least 8 feet of length is
in contact with the soil. It shall be driven to a depth of not less than 8
feet except that, where rock bottom is encountered, the electrode shall be
driven at an oblique angle not to exceed 45 degrees from the vertical or
shall be buried in a trench that is not less than 2-1/2 feet deep.
The upper
end of the electrode shall be flush with or below ground level unless the
aboveground end and the grounding electrode conductor attachment are
protected against physical damage as specified in Section 250-10."
Highlight added by me.
 
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Old 12-13-15, 08:28 PM
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Do not cut the rod. You need 8' of direct earth contact minimum. The top needs to be flush or below the surface.
 
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Old 12-14-15, 06:35 AM
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Sorry. The "cut the rod" comment was intended as a joke. I should have added one of those smiley thingys. It was not cut but I'm sure that it exceeds the 45* angle.
 
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Old 12-14-15, 07:03 AM
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When the geology is all rock there's only so much you can do. Code specifies 30" deep for horizontal rods, but it sounds like that might even be a significant challenge if you have solid granite at 48". The best solution is simply to add additional ground rods at whatever depth or angle you can feasibly achieve.
 
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Old 12-14-15, 04:21 PM
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Thanks Ben for some common sense advice. My electrician is a good guy and he knows we're prepping this house to sell. I am 100% positive that he would do nothing to jeopardize that. My questions were as much out of curiosity than anything else - like wondering what would you do if your house is sitting on surface rock?

I've done a little reading and I know the <25 ohm ground requirement but how/where is that measured?
 
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Old 12-14-15, 04:56 PM
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I've done a little reading and I know the <25 ohm ground requirement but how/where is that measured?
That IS the question.

You would normally measure between the ground rod and a known good ground. A known good ground would be a metal water service if you have city water.

The ground rod would not be connected to the service during the testing.
 
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Old 12-14-15, 06:40 PM
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The testing equipment takes time and is expensive. It is normally easier to drive a second rod and be done with it.
 
 

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