8/22/2019 nesc2007

1/22

PROPOSED CHANGES TO THE

2007 NATIONAL ELECTRICALSAFETY CODE

8/22/2019 nesc2007

2/22

Time Schedule for 2007 Edition of

NESC

July 17, 2003 Final date for receipt of proposals

Oct. 5-24, 2003 NESC Subcommittees meet

Sept. 1, 2004 NESC Preprints published

May 1, 2005 Final date for receipt of public

comments

8/22/2019 nesc2007

3/22

Time Schedule for 2007 Edition of

NESC

Oct. 2-20, 2005 NESC Subcommitteesreconsider recommendations

Jan. 15, 2006 Proposed revisions submitted toNESC Committee for ballot

May 15, 2006 NESC Committee submitsapproved revisions to ANSI

Aug. 1, 2006 2007 NESC published

8/22/2019 nesc2007

4/22

CP 2528- 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.

8/22/2019 nesc2007

5/22

CP 2715- Rule 94B7, Directly

Embedded Metal Poles

Allows directly embedded metal poles to be anacceptable grounding electrode if:

backfill is native backfill, concrete or conductivegrout,

embedment is > 5,

metal thickness is > , and

any protective coating is conductive.

8/22/2019 nesc2007

6/22

CP 2508- Rule 230, Uniform Clearance

Calculations

Moves current Rule 250 B, Figure 250-1 and Table

250-1 to new Rule 230.

Retains the ice loading districts for determiningclearances.

Changes loading districts to loading zones.

Wind loading values revert to 4th edition values.

Appendix B

8/22/2019 nesc2007

7/22

CP 2508- Rule 230, Uniform Clearance

Calculations

Wind loading values revert to 4th edition values.

Wind values are 8 psf for Heavy and Medium; 10 psf forLight.

The adder constants (0.3, 0.2 & 0.05) of Table 251-1

were deleted.

This will produce approximately the same sags as thelesser wind pressure in the 2002 edition with the adder

constant.

8/22/2019 nesc2007

8/22

CP 2630- 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 totruck 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.

8/22/2019 nesc2007

9/22

CP 2826- 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.

8/22/2019 nesc2007

10/22

CP 2737- 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.

8/22/2019 nesc2007

11/22

8/22/2019 nesc2007

12/22

EXTREME WIND LOADING

FORMULA

Load in pounds = 0.00256 (V2) (kZ) (Grf) ( I ) (Fg) (Cd) (A2)

0.00256 = Ambient air density value

V2

= Basic wind speed in miles per hour (squared) Kz = Velocity pressure exposure coefficient. This value is

defined in Tables 250-1 & 250-2 for open terrain and Tables250-3 & 250-4 for sheltered terrain.

Grf = Gust response factor defined in tables 250-1, 25-0-2,

250-3 & 250-4. I = Importance factor, 1.0 for utility structures and their

supporting facilities

Fg = Factor for Grade of Construction (0.87 for C, 1.0 for B).

Cd = Shape factor from Rule 252B2 (Rules N251A & 251B). A2 = Projected wind area squared in square feet

8/22/2019 nesc2007

13/22

8/22/2019 nesc2007

14/22

8/22/2019 nesc2007

15/22

CP 2766- Rule 250C, EXTREME WIND

Limits extreme loading on structures < 60.

Limits 0.00256V2kZGRF to 15 psf for Grade C.

Limits 0.00256V2kZGRF to 30 psf for Grade B.

8/22/2019 nesc2007

16/22

CP 2658- Rule 250D, Construction and

Maintenance Loads

Where maintenance & construction loads exceed the windand ice load:

All conductor support points shall resist the bare

conductor vertical loads expected to occur at saggingtensions times SF = 2.

All structural members supporting linemen shall be ableto support 240# vertical load in addition to the max loads

during maintenance.

When pulling thru stringing blocks, the pulling tensionmust be carefully controlled. If not, the pulling tensionshall be applied to the block attachment point timesSF=1.5.

8/22/2019 nesc2007

17/22

CP 2569- 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.

8/22/2019 nesc2007

18/22

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 limittransfer of a detrimental load onto the cable.

8/22/2019 nesc2007

19/22

CP 2815- 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/cm2, FR clothing shall be worn.

For V < 1000V, FR clothing with a min resistance of 4

cal/cm2 shall be required.

For V > 1000V, use Tables 410-1 & 410-2 or perform

an arc hazard analysis to determine FR clothing

requirements.

8/22/2019 nesc2007

20/22

8/22/2019 nesc2007

21/22

CP 2530- 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 1910.97, 1910.268

IEEE Std. C95.1-1999

8/22/2019 nesc2007

22/22

QUESTIONS?