nec 250-83

Made and Other Electrodes, NEC 250-83

	Where none of the electrodes specified in Section 250-81 is available, one or more of the electrodes specified in (b) through (d) below shall be used.
	Where practicable, made electrodes shall be embedded below permanent moisture level.
	Made electrodes shall be free from nonconductive coatings, such as paint or enamel.
	Where more than one electrode is used, each electrode of one grounding system (including that used for lightning rods) shall not be less than 6 ft (1.83 m) from any other electrode of another grounding system.
	Two or more grounding electrodes that are effectively bonded together shall be considered a single grounding electrode system.

(a) Metal Underground Gas Piping System. A metal underground gas piping system shall not be used as a grounding electrode.

(b) Other Local Metal Underground Systems or Structures. Other local metal underground systems or structures, such as piping systems and underground tanks.

(c) Rod and Pipe Electrodes. Rod and pipe electrodes shall not be less than 8 ft (2.44 m) in length, shall consist of the following materials, and shall be installed in the following manner:

(1) Electrodes of pipe or conduit shall not be smaller than 3/4-in. trade size and, where of iron or steel, shall have the outer surface galvanized or otherwise metal-coated for corrosion protection.

(2) Electrodes of rods of iron or steel shall be at least 5/8 in. (15.87 mm) in diameter. Stainless steel rods less than 5/8 in. (15.87 mm) in diameter, nonferrous rods, or their equivalent shall be listed and shall not be less than 1/2 in. (12.7 mm) in diameter.

(3) The electrode shall be installed such that at least 8 ft (2.44 m) of length is in contact with the soil. It shall be driven to a depth of not less than 8 ft (2.44 m) 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 at least 2 1/2 ft (762 mm) 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 250-117.

(d) Plate Electrodes. Each plate electrode shall expose not less than 2 sq ft (0.186 sq m) of surface to exterior soil. Electrodes of iron or steel plates shall be at least 1/4 in. (6.35 mm) in thickness. Electrodes of nonferrous metal shall be at least 0.06 in. (1.52 mm) in thickness.

(e) Aluminum Electrodes. Aluminum electrodes shall not be permitted.