PROPOSED CHANGES TO THE 2007 NATIONAL ELECTRICAL SAFETY CODE

Time Schedule for 2007 Edition of NESC July 17, 2003Final date for receipt of proposals Oct. 5-24, 2003NESC Subcommittees meet Sept. 1, 2004NESC Preprints published May 1, 2005 Final date for receipt of public comments

Time Schedule for 2007 Edition of NESC Oct. 2-20, 2005NESC Subcommittees reconsider recommendations Jan. 15, 2006Proposed revisions submitted to NESC Committee for ballot May 15, 2006NESC Committee submits approved revisions to ANSI Aug. 1, NESC published

CP Section 2, Definitions Relocates and revises the definition of “readily climbable supporting structure.” Combines “readily climbable” and “not readily climbable” under one definition. Adds the notes that clarify what structures are considered not “readily climbable” to the code.

CP Rule 94B7, Directly Embedded Metal Poles Allows directly embedded metal poles to be an acceptable grounding electrode if: backfill is native backfill, concrete or conductive grout, embedment is > 5’, metal thickness is > ¼”, and any protective coating is conductive.

CP Rule 230, Uniform Clearance Calculations Moves current Rule 250 B, Figure and Table to new Rule 230. Retains the ice loading districts for determining clearances. Changes “loading districts” to “loading zones.” Wind loading values revert to 4 th edition values. Appendix B

CP Rule 230, Uniform Clearance Calculations Wind loading values revert to 4 th edition values. Wind values are 8 psf for Heavy and Medium; 10 psf for Light. The “adder constants” (0.3, 0.2 & 0.05) of Table were deleted. This will produce approximately the same sags as the lesser wind pressure in the 2002 edition with the adder constant.

CP Rule 232B3, Clearance to Support Arms, Switch Handles and Equipment Cases Adds switch handles to the rule. Requires a clearance of 15’ above areas accessible to truck traffic and 11’ under spaces and ways accessible to pedestrians if effectively grounded. Does not address switch handles not grounded. Excepts switch handles that “do not unduly obstruct a walkway.”

CP Rule 242, Grades of Construction for Conductors Requires conductors crossing navigable waterways requiring crossing permits to be designed to Grade B construction. Proposed because of downed overhead conductors hampering rescue craft during storm recovery efforts.

CP Revision of Sections 25, 26 & 27 Proposes incorporating the Reliability Based Method for determining structure loading. Consistent with ANSI/ASCE 7. New combined ice and wind loading map. Map based on 50 year ice and wind events. Provides a new formula for extreme wind. Eliminates the 60’ exclusion from extreme wind loading.

EXTREME WIND LOADING FORMULA Load in pounds = (V 2 ) (k Z ) (G rf ) ( I ) (F g ) (C d ) (A 2 ) = Ambient air density value V 2 = Basic wind speed in miles per hour (squared) Kz = Velocity pressure exposure coefficient. This value is defined in Tables & for open terrain and Tables & for sheltered terrain. Grf = Gust response factor defined in tables 250-1, , & I = Importance factor, 1.0 for utility structures and their supporting facilities F g = Factor for Grade of Construction (0.87 for C, 1.0 for B). Cd = Shape factor from Rule 252B2 (Rules N251A & 251B). A 2 = Projected wind area squared in square feet

CP Rule 250C, EXTREME WIND Limits extreme loading on structures < 60’. Limits V 2 k Z G RF to 15 psf for Grade C. Limits V 2 k Z G RF to 30 psf for Grade B.

CP Rule 250D, Construction and Maintenance Loads Where maintenance & construction loads exceed the wind and ice load: All conductor support points shall resist the bare conductor vertical loads expected to occur at sagging tensions times SF = 2. All structural members supporting linemen shall be able to support 240# vertical load in addition to the max loads during maintenance. When pulling thru stringing blocks, the pulling tension must be carefully controlled. If not, the pulling tension shall be applied to the block attachment point times SF=1.5.

CP Table 253-1, Rule 261A3, Table 261-1A, Fiber-Reinforced Polymer Structures Addresses the strength requirements and the strength factors for fiberglass poles and crossarms.

CP2622- Rule 351C, Location & Routing, Other Conditions In response to IR 524. Addresses the location of DB UG cable under an above ground pool. Recommends that DB UG cable should not be installed directly under buildings or other structures unless the structure is suitably supported to limit transfer of a detrimental load onto the cable.

CP Rule 410, General Requirements for Employers Requires that by 2009, an arc assessment be performed for employees that work on or near energized parts. If exposure > 2 cal/cm 2, FR clothing shall be worn. For V < 1000V, FR clothing with a min resistance of 4 cal/cm 2 shall be required. For V > 1000V, use Tables & or perform an arc hazard analysis to determine FR clothing requirements.

CP Rule 431C, Communication Antennas Prohibits workers from being exposed to radiation levels greater than those set forth by the administrative authority for 3 kHz < f < 3 GHz. OHSA , IEEE Std. C

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