Ground Rod Installation

Grouch

Grouch

Senior Member
Location
New York, NY
The attached image is from the NEC handbook, showing the ground rod fully buried. In electrical rooms of buildings in NYC, you always see a few inches of the ground rod above the slab, as well as the clamp where the GEC connects, before penetrating the slab. How many inches of the ground rod is allowed to be above the slab? And is it stated in Article 250?

Ground rod.jpeg
 
NEC 250.53 states that ground rods must be driven so that at least 8 feet are in contact with the earth. However, some portion of the rod (typically a few inches) may be exposed above grade to facilitate access to the connection point for the grounding electrode conductor (GEC). There is no requirement that I know of that states how many inches are allowed above the slab.

It is also important to note that you can only install a ground rod at an angle when a full vertical installation is not possible.
 
IEEE 80/23 9.4 Basic aspects of grid design
c) A typical grid system for a substation may include 4/0 bare copper conductors buried 0.3 m to 0.5 m (12 in to 18 in) below grade, spaced 3 m to 7 m (10 ft to 20 ft) apart, in a grid pattern. At cross-connections, the conductors would be securely bonded together. Ground rods may be at the grid corners and at junction points along the perimeter. Ground rods may also be installed at major equipment, especially near surge arresters. In multilayer or high resistivity soils, it might be useful to use longer rods or rods installed at additional junction points.
NESC C2/2007 094. Grounding electrodes. B. Made electrodes 2. Driven rods.
c. Driven depth shall be not less than 2.45 m (8 ft). The upper end shall be flush with or
below the ground level unless suitably protected.
EXCEPTION 1: Where rock bottom is encountered, driven depth may be less than 2.45 m (8 ft), or other types of electrode may be employed.
EXCEPTION 2: When contained within pad-mounted equipment, vaults, manholes, or similar enclosures, the driven depth may be reduced to 2.3 m (7.5 ft).
If the connections between rods and copper conductor is through mechanical connectors a handhole may be installed in order to use this for ground tests. If the connection is of cadweld type the ground rod end will be at copper conductor level.
 
baserunner4 said:
NEC 250.53 states that ground rods must be driven so that at least 8 feet are in contact with the earth. However, some portion of the rod (typically a few inches) may be exposed above grade to facilitate access to the connection point for the grounding electrode conductor (GEC).
Click to expand...
How can an 8' rod have 8' in contact with the earth and still have a few inches exposed above grade?
 
Making sure I follow: the NEC doesn't state how much of the ground rod can be exposed on the upper end. So it can be a few inches... as long as the ground rod is 9 or 10 feet long, we meet the requirements of having at least 8 feet of ground rod buried. Do I have this correct?
 
Grouch1980 said:
Making sure I follow: the NEC doesn't state how much of the ground rod can be exposed on the upper end. So it can be a few inches... as long as the ground rod is 9 or 10 feet long, we meet the requirements of having at least 8 feet of ground rod buried. Do I have this correct?
Click to expand...
That is the way the code is written, so technically this is correct. Any protrusion above grade on an 8 ft ground rod would be an inspector looking the other way.
 
Grouch1980 said:
Making sure I follow: the NEC doesn't state how much of the ground rod can be exposed on the upper end. So it can be a few inches... as long as the ground rod is 9 or 10 feet long, we meet the requirements of having at least 8 feet of ground rod buried. Do I have this correct?
Click to expand...
Keep in mind that a ground clamp attached to a rod that is exposed is often likely to be subject to physical damage and would therefore require some sort of protection. By installing it flush or below the ground the protection would no longer be required. Then there is also the issue of proving to the inspector that the rod is actually longer than 8' when it is not installed all the way into the earth.
250.10 Protection of Ground Clamps and Fittings.
Ground clamps or other fittings exposed to physical damage shall be enclosed in metal, wood, or equivalent protective covering.
Click to expand...
 
infinity said:
How can an 8' rod have 8' in contact with the earth and still have a few inches exposed above grade?
Click to expand...
The NEC does not specify the length of the rod to use. In this case, a 10' rod would be required, or two 8' rods would need to be connected together. There is no concern of physical damage, as this is located in a corner of an electrical room in NYC, most likely in a basement. Flush installation is not possible. Visual inspection is required, and the rod is embedded in a concrete pad. Therefore, the size is inspected before the concrete pour.
 
baserunner4 said:
The NEC does not specify the length of the rod to use. In this case, a 10' rod would be required
Click to expand...
If you are going to leave a few inches above the ground you are correct.
baserunner4 said:
or two 8' rods would need to be connected together.
Click to expand...
You would probably need two 10' rods as well unless you have the right equipment to prove one is 25 ohms or less.
 
Larry, that was not the question. How you get it to comply with words of the code can be achieved in a number of ways.

Not to mention you are repeating what you already said
 
You must log in or register to reply here.
Top