1. Grounding Electrodes

2. Definition of a Grounding Electrode
Article 100 –
Grounding Electrode:
A conducting object through which a direct connection to earth is established.

3. 250.4 General Requirements for Grounding and Bonding
250.4(A)(1) Electrical System Grounding
Electrical systems that are grounded shall be connected to earth in a manner that will limit the voltage imposed by lightning, line surges, or unintentional contact with higher-voltage lines and that will stabilize the voltage to earth during normal operations.
Informational Note: An important consideration for limiting the imposed voltage is the routing of bonding and grounding electrode conductors so that they are not any longer than necessary to complete the connection without disturbing the permanent parts of the installation and so that unnecessary bends and loops are avoided.

4. 250.52 Grounding Electrodes (A) Electrodes Permitted for Grounding
Metal Underground Water Pipe
Metal Frame of Building or Structure
Concrete Encased Electrode
Ground Ring
Rod Electrodes and Pipe Electrodes
Other Listed Electrodes
Plate Electrode
Other Local Metal Underground Systems or Structures

5. 250.52(A)(1) Metal Underground Water Pipe
Shall be in direct contact with a minimum 10 ft of earth
Shall include any well casing effectively bonded to the pipe
Shall be electrically continuous by bonding around insulating joints

6. 250.52(A)(2) Metal Frame of Building or Structure
Provides two conditions under which the metal frame of a building or structure can be judged suitable:
10 ft or more of a single structural metal member in direct contact with the earth or in concrete directly contacting the earth
Use of hold-down bolts securing the structural steel to a concrete encased electrode that complies with (A)(3) and is located in the support footing or foundation.

7. 250.52(A)(3) Concrete-Encased Electrode
A concrete-encased electrode shall consist of at least 6.0 m (20 ft) of either:
One or more bare or galvanized or other electrically conductive coated steel reinforced bars or rods not less than 13mm(1/2 in.) in diameter, installed in one continuous length, or if in multiple pieces connected together by the usual tie wire or other effective connection method
Bare copper conductor not smaller than 4 AWG
Encased by at least 50mm (2 in.) of concrete Electrode shall be:
- at least 20 ft in length
- reinforcing bars or rods not less than ½” in diameter
- bare copper conductor not less than #4 AWG
Reinforcing bars may be bonded together by the usual steel tie wires

8. 250.52(A)(4) Ground Ring
A ground ring encircling the building or structure in direct contact with the earth, consisting of at least 6m (20 ft)
of bare copper conductor
not smaller than 2 AWG.

9. 250.52(A)(5) Rod and Pipe Electrodes
Electrodes of Pipe
- 2.44m (8 ft) minimum length
- 3/4 in. “trade size” minimum diameter
- be of iron or steel and shall have the outer surface galvanized or otherwise metal-coated for corrosion protection
Electrodes of Rod
- 8 ft minimum length
- 5/8 in. (0.625”) minimum diameter
- 1/2 in. (0.500”) minimum diameter for stainless steel, and copper-coated or zinc-coated steel when listed

10. 250.52(A)(7) Plate Electrodes
Plate electrodes shall expose not less than 0.186m2 (2 ft2) of surface to exterior soil
Electrodes of bare or conductively coated iron or steel plate shall be at least 6.4m (1/4 in.) thick
Solid, uncoated, non-ferrous electrodes shall be at least 1.5mm (.06 in.) thick

11. 250.52(A)(8) Other Local Metal Underground Systems or Structures
May include piping systems, underground tanks, and underground well casings not effectively grounded to metal water pipe.

12. 250.53 Grounding Electrode System Installation Summary
If practicable, rod, pipe and plate electrodes shall be installed below permanent moisture level
Grounding electrodes shall be spaced not less than 1.83m (6 ft) apart where more than one electrode is specified
Informational Note: the paralleling efficiency of rods is increased by spacing them twice the length of the longest rod.
A bonding jumper shall be sized and spaced according to NEC
If a metal underground water pipe is used, it shall meet NEC requirements
A bonding jumper that is the sole connection to the supplemental grounding electrode shall not be required to be larger than 6 AWG copper wire.
Ground rings and plate electrodes shall be installed not less than 750mm (30 in.) below the surface of earth.

13. ANSI/NEMA GR 1-2007 Zinc Coated Ground Rod Electrodes
Diameter Ranges for Zinc Coated Steel Rods
Finish Diameter Range, Inches
Trade Sizes Minimum Maximum 5/ 3/
Note: The above dimensions may vary if ground rod is certified to a U.S. nationally recognized standard.

14. ANSI/NEMA GR 1–2007 Copper-Bonded Ground Rod Electrodes
Diameter Ranges for Copper-Bonded Steel Rods
Finish Diameter Range, Inches Trade Sizes Minimum Maximum 1/ 5/ 3/

15. ANSI/NEMA GR 1–2007 Copper-Bonded Ground Rod Electrodes
Thread Specifications
Trade Sizes Thread Length Thread B Profile (in. +1/8, -1/16) (UNC)
1/ /16 9/16-12
5/ /16 5/8-11
3/ /4 3/4-10 /

16. Properties of ANSI/NEMA GR-1 Zinc-Coated Ground Electrodes
Zinc-Coated Steel
Straightness variation ≤ inches in 5 ft
Steel core tensile strength ≥ 80k psi
Zinc deposit shall be minimum inches
Legibly marked with manufacturer’s identification
ASTM Standards -
ASTM A 370 – Tensile strength
ASTM A 123 or ASTM A 153 – Zinc coating
ASTM E 376 – Coating thickness measurement

17. Properties of ANSI/NEMA GR-1 Copper-Bonded Ground Electrodes
Copper-Bonded Steel
Straightness variation ≤ 0.25 inches in 5 ft
Steel core tensile strength ≥ 80k psi
Copper deposit shall be minimum inches
Legibly marked with manufacturer and catalog or equivalent designation
ASTM Standards -
ASTM A 370 – Tensile strength
ASTM E 376 – Coating thickness measurement

18. Resistance of Electrodes
Water pipe – no NEC requirements
Building steel – no NEC requirements
Concrete encased – no NEC requirements
Ground ring – no NEC requirements
Rod, Pipe, and Plate – 25 ohms or less
A second rod is required if the first rod’s resistance is non-compliant
NEC Section
Supplemental Electrodes for metal underground water pipe
- Where of pipe, rod or plate – NEC (A) (2) is applicable

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