ground rod
#1
12-13-15, 01:36 PM
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?
#4
12-13-15, 07:51 PM
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?
Not that I'm planning on moving anything, but how deep would the trench have to be?
#5
12-13-15, 08:36 PM
Member
NEC Article 250:
Highlight added by me.
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."
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."
#8
12-14-15, 08:03 AM
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.
#9
12-14-15, 05:21 PM
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?
I've done a little reading and I know the <25 ohm ground requirement but how/where is that measured?
#10
12-14-15, 05:56 PM
Group Moderator
I've done a little reading and I know the <25 ohm ground requirement but how/where is that measured?
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.
