by Jim White and Ron Widup, Shermco Industries
2012 Edition NFPA 70E
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INFORMATIVE ANNEXES IN THE 70E
Annexes in NFPA 70E are used to supplement the information in the standard and are not part of the standard insomuch as they are not mandatory. The new title for the annex section is Informative Annexes. While people do not often review the annexes, perhaps because they do not recognize their importance, the annexes help readers to better understand the standard and the reasons the NFPA 70E committee has made some of its decisions.
Annex A is a listing of all standards referenced by NFPA 70E. This list includes ANSI standards, IEEE standards, ICRP standards, ASTM standards, IEC standards, and the NEC. The most recent versions (as of the ROC/ Second Draft meeting) are used as references for each standard.
Annex B contains a listing of informational references, which may also include standards. The primary difference between Annex A and Annex B is that the standards within Annex A are considered part of the standard and thus include mandatory elements, and the documents listed in Annex B are informational only.
Annex C has information about limits of approach. Information contained within Articles 110 and 130 are expanded upon in Annex C, and more detail is provided about the shock approach boundaries. As an example, C.2.1 discusses the following:
• The distances in columns 2 through 5 of Tables 130.4(C)(a) and (b) were derived from the basic minimum air insulation distances in IEEE Standard 4, Standard Techniques for High Voltage Testing, Appendix 2B for voltages 72.5 kV and less, while IEEE Standard 516, Guide for Maintenance Methods on Energized Power Lines was used for voltages above 72.5 kV).
• Column 2, Limited Approach Boundary (Exposed Movable Conductor), uses OSHA’s requirement stated in 29 CFR 1910.333(c)(3)(i).
• Column 3, Limited Approach Boundary (Exposed Fixed Circuit Part) comes from NEC Table 110.26(A)(1) for 151 volts to 600 volts, NEC Table 110.34(A) for 750 volts to 145 kV and OSHA 1910.333 for voltages above 145 kV.
• Column 4, Restricted Approach Boundary, primarily comes from the National Electrical Safety Code, ANSI C2 and
• Column 5, Prohibited Approach Boundary, is from a combination of experience and NEC Tables 230.51(C) and 490.24.
Annex D, Incident Energy and Arc Flash Boundary Calculation Methods, has information concerning several methods that can be used to calculate incident energy and the arc flash boundary with IEEE 1584, Guide for Performing Arc-Flash Hazard Calculations being one of them. Each method discussed has limitations of use, and in some cases, one may be more appropriate than another.
As an example, IEEE 1584 can only be used to determine incident energy for voltages from 208 volts through 15,000 volts
in metalenclosed equipment (arc-in-a-box) with short-circuit currents between 700 amperes to 106,000 amperes.
The Doughty/Neal method can be used to determine incident energy for three-phase systems of 600 volts and less, when the shortcircuit current is between 16,000 amperes and 50,000 amperes.
The Ralph Lee method is used for determining incident energy on a three-phase system above 15,000 volts in open air. The text portion of IEEE 1584 is included as part of Annex D for reference.
Table D.2 contains very useful information, in that it estimates the arc-flash boundaries for various system voltages and short-circuit currents in a large petrochemical plant. This should be of use to almost anyone who works in a large facility and wants to know the risk of an arc-flash burn, even though the table applies specifically to petrochemical plants.
Some of the arc-flash boundaries are eyeopening, and one should take the time to read and understand Annex D.
One change to Annex D is in D.6 Calculation of Incident Energy Exposure Greater Than 600 V for an Arc Flash Hazard Analysis.
Often the software for arc-hazard studies is set at a twosecond maximum fault duration, which is normally satisfactory for the purposes of arcflash analysis. The fault duration is based on the belief that in two seconds the worker is either on his way out of the room or the exposure has passed, but that may not always be the case.
For example, a person working inside a cabinet or in an area that has restricted access such as a bucket truck as described in the following example may be exposed to an arc for longer than two seconds. In situations such as this, the worker has little choice other than to do the best he can to protect himself until the danger passes. Fortunately, most such incidents would probably be from a single-phase fault; therefore, the incident energy would be reduced from a three-phase arc. However, the incident energy is proportional to time, so the longer the arc lasts, the more heat is produced.
The wording for this new section is “If the arcing time, t, in Equation D.7.3(c) is longer than 2 seconds, consider how long a person is likely to remain in the location of the arc flash. It is likely that a person exposed to an arc flash will move away quickly if it is physically possible, and 2 seconds is a reasonable maximum time for calculations. Sound engineering judgment should be used in applying the 2-second maximum clearing time, because there could be circumstances where an employee’s egress is inhibited.
For example, a person in a bucket truck or a person who has crawled into equipment will need more time to move away.”
Annex E through Annex P Although there are many more informative and important annexes within the 70E, space restrictions unfortunately prevent us from detailing each one.
Readers should take the time to study and understand the remaining annexes.
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SUMMARY
Information in the 70E standard and the annexes is constantly changing. The NFPA is moving to an on-line submission and review system to streamline the process, and the 70E changes approximately every three years. Proposals (Public Input) must be submitted before the new closing date of June 22, 2012. Some items could use editing for clarification, and reader suggestions are welcome to help improve this edition. After all, this is your safety standard. Help make it a better by providing constructive inputs for change.
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Ron Widup and Jim White are NETA’S representatives to NFPA Technical Committee 70E (Electrical Safety Requirements for Employee Workplaces).Both gentlemen are employees of Shermco Industries in Dallas, Texas a NETA Accredited Company.
Ron Widup is President of Shermco and has been with the company since 1983. He is a Principal member of the Technical Committee on “Electrical Safety in the Workplace” (NFPA 70E) and a Principal member of the National Electrical Code (NFPA 70) Code Panel 11. He is also a member of the technical committee “Recommended Practice for Electrical Equipment Maintenance” (NFPA 70B), and a member of the NETA Board of Directors and Standards Review Council.
Jim White is nationally recognized for technical skills and safety training in the electrical power systems industry.
He is the Training Director for Shermco Industries, and has spent the last twenty years directly involved in technical skills and safety training for electrical power system technicians. Jim is a Principal member of NFPA 70B representing Shermco Industries, NETA’s alternate member of NFPA 70E, and a member of ASTM F18 Committee “Electrical Protective Equipment for Workers.”
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