There were 3,688 proposals for changes to the newest National Electrical Code (NEC) and 2,349 comments processed by the National Fire Protection Association (NFPA) staff at NFPA headquarters in Quincy, Mass. The following is part four in a series of significant changes for the 2008 NEC. Part one appeared in the July 2007 issue of ELECTRICAL CONTRACTOR, part two appeared in the October 2007 issue, and part three appeared in the March 2008 issue. The 2008 NEC was formally adopted in August 2007, and new copies were available from the National Electrical Contractors Association (NECA) and the National Fire Protection Association (NFPA) as of September 2007.

The following are some of the most important changes. Strikethrough text shows deletions, and underlined text shows additions. Commentary denoted by red text also follows some changes for explanation.

2005 NEC—250.32 Buildings or Structures Supplied by Feeder(s) or Branch Circuit(s).

(B) Grounded Systems. For a grounded system at the separate building or structure, the connection to the grounding electrode and grounding or bonding of equipment, structures, or frames required to be grounded or bonded shall comply with either 250.32(B)(1) or (B)(2).

(1) Equipment Grounding Conductor. An equipment grounding conductor as described in 250.118 shall be run with the supply conductors and connected to the building or structure disconnecting means and to the grounding electrode(s). The equipment grounding conductor shall be used for grounding or bonding of equipment, structures, or frames required to be grounded or bonded. The equipment grounding conductor shall be sized in accordance with 250.122. Any installed grounded conductor shall not be connected to the equipment grounding conductor or to the grounding electrode(s).

(2) Grounded Conductor. Where (1) an equipment grounding conductor is not run with the supply to the building or structure, (2) there are no continuous metallic paths bonded to the grounding system in each building or structure involved, and (3) ground-fault protection of equipment has not been installed on the supply side of the feeder(s), the grounded conductor run with the supply to the building or structure shall be connected to the building or structure disconnecting means and to the grounding electrode(s) and shall be used for grounding and bonding of equipment, structures, or frames required to be grounded or bonded. The size of the grounded conductor shall not be smaller than the larger of either of the following:

(1) That required by 220.61

(2) That required by 250.122

2008 NEC—250.32 Buildings or Structures Supplied by Feeder(s) or Branch Circuit(s).

(B) Grounded Systems. For a grounded system at the separate building or structure, an equipment grounding conductor as described in 250.118 shall be run with the supply conductors and be connected to the building or structure disconnecting means and to the grounding electrode(s). The equipment grounding conductor shall be used for grounding or bonding of equipment, structures, or frames required to be grounded or bonded. The equipment grounding conductor shall be sized in accordance with 250.122. Any installed grounded conductor shall not be connected to the equipment grounding conductor or to the grounding electrode(s).

Exception: For existing premises wiring systems only, the grounded conductor run with the supply to the building or structure shall be permitted to be connected to the building or structure disconnecting means and to the grounding electrode(s) and shall be used for grounding or bonding of equipment, structures, or frames required to be grounded or bonded where all the requirements of (1), (2), and (3) are met:

(1) An equipment grounding conductor is not run with the supply to the building or structure,

(2) There are no continuous metallic paths bonded to the grounding system in each building or structure involved, and

(3) Ground-fault protection of equipment has not been installed on the supply side of the feeder(s),

Where the grounded conductor is used for grounding in accordance with the provision of this exception, the size of the grounded conductor shall not be smaller than the larger of either of the following:

(1) That required by 220.61

(2) That required by 250.122

Section 250.32(B)(2) permitted the equipment grounding conductor to be deleted in an installation where there is no continuous metallic path bonded to the grounding system from building or structure to building or structure. The grounded conductor would then be used for a path back to the original building or structure for any fault current. There was no way to effectively ensure that the two buildings or structures would remain isolated in the future. This change will help reduce the number of designs or installations where inappropriate neutral-to-ground connections can and often do happen at a later date by the installation of a grounding path between the buildings or structures. The comment has deleted (1) and the lead-in text in (B) since the proposal has deleted 250.32(B)(2). The phrase “new or existing buildings or structures only” was deleted in the exception to have the exception apply only to existing premises wiring systems.

2005 NEC—250.52 Grounding Electrodes.

(A) Electrodes Permitted for Grounding.

(2) Metal Frame of the Building or Structure. The metal frame of the building or structure, where any of the following methods are used to make an earth connection:

(1) 3.0 m (10 ft) or more of a single structural metal member in direct contact with the earth or encased in concrete that is in direct contact with the earth

(2) The structural metal frame is bonded to one or more of the grounding electrodes as defined in 250.52(A)(1), (A)(3), or (A)(4)

(3) The structural metal frame is bonded to one or more of the grounding electrodes as defined in 250.52(A)(5) or (A)(6) that comply with 250.56, or

(4) Other approved means of establishing a connection to earth.

2008 NEC—250.52 Grounding Electrodes.

(A) Electrodes Permitted for Grounding.

(2) Metal Frame of the Building or Structure. The metal frame of the building or structure that is connected to the earth by any of the following methods:

(1) 3.0 m (10 ft) or more of a single structural metal member in direct contact with the earth or encased in concrete that is in direct contact with the earth

(2) By connecting the structural metal frame to the reinforcing bars of a concrete-encased electrode as provided in 250.52(A)(3) or ground ring as provided in 250.52(A)(4)

(3) By bonding the structural metal frame to one or more of the grounding electrodes as defined in 250.52(A)(5) or (A)(6) that comply with 250.56 or

(4) By other approved means of establishing a connection to the earth

This section in the 2005 NEC created a possible problem using the metal water pipe as a method of effectively making the metal frame of the building or structure into a grounding electrode. Where only the metal water pipe and the metal frame of the building or structure are the electrodes, 250.53(D)(2) requires an additional supplemental electrode, of which one can be the metal of a building or structure. Where the building metal water piping system is replaced with nonmetallic water pipe, the building metal would no longer be an electrode, and total loss of an electrode for the building electrical system would be the result. The text was revised to correct this problem by requiring the building metal frame to be in direct contact with the earth for 10 feet or more, use the concrete-encased electrode, the ground ring, rods, pipe or plate electrodes, or other approved means of connecting to earth.

2005 NEC—250.52 Grounding Electrodes.

(A) Electrodes Permitted for Grounding.

(3) Concrete-Encased Electrode. An electrode encased by at least 50 mm (2 in.) of concrete, located within and near the bottom of a concrete foundation or footing that is in direct contact with the earth, consisting of at least 6.0 m (20 ft.) of one or more bare or zinc galvanized or other electrically conductive coated steel reinforcing bars or rods of not less than 13 mm (½ in.) in diameter, or consisting of at least 6.0 m (20 ft.) of bare copper conductor not smaller than 4 AWG. Reinforcing bars shall be permitted to be bonded together by the usual steel tie wires or other effective means.

2008 NEC—250.52 Grounding Electrodes.

(A) Electrodes Permitted for Grounding.

(3) Concrete-Encased Electrode. An electrode encased by at least 50 mm (2 in.) of concrete, located horizontally near the bottom or vertically, and within that portion of a concrete foundation or footing that is in direct contact with the earth, consisting of at least 6.0 m (20 f.t) of one or more bare or zinc galvanized or other electrically conductive coated steel reinforcing bars or rods of not less than 13 mm (½ in.) in diameter, or consisting of at least 6. 0 m (20 ft.) of bare copper conductor not smaller than 4 AWG. Reinforcing bars shall be permitted to be bonded together by the usual steel tie wires or other effective means. Where multiple concrete-encased electrodes are present at a building or structure, it shall be permissible to bond only one into the grounding electrode system.

This change permits the concrete-encased electrode to be located horizontally near the bottom of the footing or vertically within the portion of the footing that is in direct contact with the earth, rather than just horizontally within 2 inches of the bottom of the footing. An additional sentence has been added recognizing that there may be more than one concrete-encased electrode and thus only requiring one of the those to be bonded into the grounding electrode system.

ODE is a staff engineering associate at Underwriters Laboratories Inc., in Research Triangle Park, N.C. He can be reached at 919.549.1726 or at [email protected]. JAMES G. STALLCUP is the CEO of Grayboy Inc., which develops and authors publications for the electrical industry and specializes in classroom training on the NEC and OSHA, as well as other standards. Contact him at 817.581.2206. JAMES W. STALLCUP is vice president and senior editor at Grayboy.