NESC-2012-Part 4: Summary of Change Proposals
NESC-2012 change proposals have been published and are available for comment through May 1, 2010. Subcommittee 8, Work Rules Sections 40-44, is responsible for the changes to Part 4 of the NESC. The main change proposal includes a requirement for employers to determine potential electric arc exposures for employees who work on or near lines, parts or equipment 50- 1,000 volts. NESC-2007 does not specifically require employers to perform an arc hazard analysis on low-voltage systems so this will be a major change for 2012.
According to the 2012 proposals, NESC Subcommittee 8 established a Low Voltage Arc Flash Work Group (WG) to evaluate the necessary minimum clothing or clothing system requirements for employees working on energized lines and parts operating at voltages less than 1,000V and to develop a change proposal if needed. Based on utility specific tests, which are included in the proposals, and the application of an accepted industry standard (IEEE-1584-2002), the WG committee included the low-voltage system changes.
A new table 410-1 has been added for low voltages (50 to 1,000 volts) to offer employers the option of using tabulated values for clothing and clothing systems in lieu of performing an arc hazard analysis. The table identifies three operating voltages, including 50-250V, 251-500V and 501-1,000V, and is based on maximum fault current of 51 kA. Arc exposures indicate clothing and clothing system requirements of 8-60 cal/cm2 for metal-clad switchgear and motor control centers and 20-30 cal/cm2 for self-contained meters, pad-mounted transformers and panels and cabinets over 250V.
The new table (410-1) uses an 18-inch worker separation, which is unlike the existing higher voltage tables that use a 15-inch worker separation. The WG committee based the change on the application of IEEE 1584 test methodologies and typical working distances for low-voltage motor control centers and panel boards. The employee working distance is based on the incident energy on the worker’s face and body, not on the hands and arms.
Protective Clothing and PPE
Clause 9, flame-resistant protective clothing and personal protective equipment, is being proposed. It is being added to give more information on the intense thermal energy workers may be subjected to during an electric arc. The clause gives good methodology for risk factors to consider such as equipment condition, work methods, task elements, incident energy specifics and the flash hazard analysis. The clause also contains a number of low-voltage system evaluations providing incident energy levels for typical transformer installations.
Other proposed changes include but are not limited to a specific requirement to conduct a job briefing, an addition of MAD (minimum approach distance) tables, further comments on using IEEE 516-2009 for updated MAD distances, and some added notes on temporary protective grounding methods.
To read and comment on the proposed changes, IEEE offers for purchase change proposals for the 2012 edition. All comments must be submitted electronically through the following Web site: http://standards.ieee.org/nesc/rp/welcome.html.
References: NESC-2012- Change Proposals- Part 4 Rules for the Operation of Electric Supply and Communication Lines and Equipment.
About the Author: Pam Tompkins, a Certified Safety Professional and Certified Utility Safety Administrator, is President of SET Solutions in Lexington, South Carolina. The company specializes in helping small- to medium-size electric utilities comply with safety and training requirements. Prior to forming SET in 2000, Tompkins worked in the electric utility industry for more than 20 years.