Expand All
TOC Search:
NEMA ABP 8-2016 Avoid Arc-Flash Occurrences by Following Industry Standards, 2016
- /
- A NEMA Low Voltage Distribution Equipment Section Document
- ABP 8-2016
- Avoid Arc Flash Occurrencesby Following Industry Standards
- Published by
- National Electrical Manufacturers Association
- 1300 North 17th Street, Suite 900
- Rosslyn, Virginia 22209
- © 2016 National Electrical Manufacturers Association. All rights, including translation into other languages, reserved under the Universal Copyright Convention, the Berne Convention for the Protection of Literary and Artistic Works, and the International and Pan American copyright conventions.
- NOTICE AND DISCLAIMER
- The information in this publication was considered technically sound by the consensus of persons engaged in the development and approval of the document at the time it was developed. Consensus does not necessarily mean that there is unanimous agreement among every person participating in the development of this document.
- NEMA standards and guideline publications, of which the document contained herein is one, are developed through a voluntary consensus standards development process. This process brings together volunteers and/or seeks out the views of persons who have an interest in the topic covered by this publication. While NEMA administers the process and establishes rules to promote fairness in the development of consensus, it does not write the document and it does not independently test, evaluate, or verify the accuracy or completeness of any information or the soundness of any judgments contained in its standards and guideline publications. NEMA disclaims liability for any personal injury, property, or other damages of any nature whatsoever, whether special, indirect, consequential, or compensatory, directly or indirectly resulting from the publication, use of, application, or reliance on this document.
- NEMA disclaims and makes no guaranty or warranty, express or implied, as to the accuracy or completeness of any information published herein, and disclaims and makes no warranty that the information in this document will fulfill any of your particular purposes or needs. NEMA does not undertake to guarantee the performance of any individual manufacturer or seller’s products or services by virtue of this standard or guide.
- In publishing and making this document available, NEMA is not undertaking to render professional or other services for or on behalf of any person or entity, nor is NEMA undertaking to perform any duty owed by any person or entity to someone else. Anyone using this document should rely on his or her own independent judgment or, as appropriate, seek the advice of a competent professional in determining the exercise of reasonable care in any given circumstances. Information and other standards on the topic covered by this publication may be available from other sources, which the user may wish to consult for additional views or information not covered by this publication.
- NEMA has no power, nor does it undertake to police or enforce compliance with the contents of this document. NEMA does not certify, test, or inspect products, designs, or installations for safety or health purposes. Any certification or other statement of compliance with any health or safety-related information in this document shall not be attributable to NEMA and is solely the responsibility of the certifier or maker of the statement.
- Foreword
- This is an update to a NEMA white paper originally published in 2003. To ensure that a meaningful publication was being developed, draft copies were sent to a number of groups within NEMA having an interest in this topic. Their resulting comments and suggestions provided vital input prior to final NEMA approval and resulted in a number of substantive changes in this publication. This publication will be periodically reviewed by the Molded Case Circuit Breaker Product Group of the Low Voltage Distribution Equipment Section of NEMA for any revisions necessary to keep it up to date with advancing technology. Proposed or recommended revisions should be submitted to:
- Senior Technical Director, Operations
- National Electrical Manufacturers Association
- 1300 North 17th Street, Suite 900
- Rosslyn, VA 22209
- This white paper was developed by the Molded Case Circuit Breaker Product Group of the Low Voltage Distribution Equipment Section of NEMA. Approval of this white paper does not necessarily imply that all members of the Product Group voted for its approval or participated in its development. At the time it was approved, the Molded Case Circuit Breaker Product Group had the following members:
- ABB Inc.—Wichita Falls, TX
- Eaton Corporation—Pittsburgh, PA
- General Electric—Plainville, CT
- Siemens Industry, Inc.—Norcross, GA
- Schneider Electric USA—Andover, MA
- 1 Introduction
- The hazards of arc flash have received considerable attention in recent time for a number of reasons. When an arcing fault occurs, the harmful results can be devastating and deadly for those who are not properly prepared. Because of the potentially long-term effects, not only is the individual impacted, but also the family and employer. Equipment damage is usually considerable, frequently resulting in extended down time for the installation. Awareness of this hazard has arisen through industry forums such as the IEEE IAS Electrical Safety Workshop and NFPA training conferences. Industry codes and standards have also included measures to reduce the effects of arc flash. These codes and standards help facility operators to take preventive steps.
- The purpose of this paper is to introduce the nature of the hazard and the industry codes and standards that address arc flash. It also introduces the requirements with which facilities must comply.
- 2 The Arc-Flash Hazard
- NFPA 70E-2015, Standard for Electrical Safety in the Workplace defines the arc-flash hazard as “a dangerous condition associated with the possible release of energy caused by an electric arc.” An arc flash is an explosion involving an electric arc operating at temperatures of several thousand degrees Celsius and a pressure wave created by the arc. Within a few milliseconds, the energy from this explosion can cause severe burns and damage to hearing, vision, taste and smell. Molten metal particles, equipment parts and other loose items are expelled from the arc area. As a result, multiple trauma effects can occur that frequently prevent the worker from returning to work and may cause hardship for the family in relationships and financial issues, as well as medical treatment issues. These effects sometimes result in death.
- Many electricians “take pride” in their ability to work on energized equipment without incident. Perhaps they and their employers are not aware of the risk they are taking. One unexpected condition can initiate the explosion, which is over before reaction time permits escape. Appropriate training and preparation can be done to minimize the effects of an arc-flash event. The potential hazardous energy associated with an arc flash can be calculated. Personal protective equipment (PPE) intended for use in the environment can be used. In fact, these steps of performing the calculations, providing the training, preparation and PPE are now industry requirements.
- 3 Industry Standards
- The primary industry standards that address the arc-flash hazard are these.
- OSHA, 29 Code of Federal Regulations Part 1910, Subpart S
- NFPA 70E, Standard for Electrical Safety Requirements for Employee Workplaces®
- ANSI/NFPA 70, National Electrical Code® (NEC)
- IEEE 1584, Guide for Performing Arc-Flash Hazard Calculations
- The Occupational Safety & Health Administration (OSHA) was created to assure safe and healthful working conditions for working men and women by setting and enforcing standards and by providing training, outreach, education and assistance. OSHA 29 CFR Part 1910.333 states in part that “Safety related work practices shall be employed to prevent electric shock or other injuries resulting from either direct or indirect electrical contacts when work is performed near or on equipment or circuits which are or may be energized…” Although a number of related requirements are included within OSHA standards, OSHA field personnel also reference the requirements of NFPA 70E to enforce safety related to arc flash.
- NFPA 70E might be thought of as a “how to” standard. It provides guidance on specific steps that must be taken to comply with the more general OSHA requirements. The NFPA 70E recognizes that there are circumstances that allow working on live, energized electrical equipment. As a result, recommendations and requirements are defined for the levels of protective systems and apparatus that must be in place when personnel are working near live energized electrical equipment. Strict guidelines are outlined in NFPA 70E for the various levels of PPE that must be worn by personnel in certain hazardous situations.
- IEEE 1584 provides definitive calculation steps in support of NFPA 70E. It provides a method to calculate incident energy from which decisions about the kind of PPE needed are made. The method takes into account the key role of the interrupting time of the overcurrent protective device. It also includes other factors such as the presence of an enclosure for the overcurrent protective device, the gap between conductors, the type of grounding system, and the distance from the possible arcing point to a person.
- In NEC Section 110.16, Arc-Flash Hazard Warning, electrical equipment, such as switchboards, panelboards, industrial control panels, meter socket enclosures, and motor control centers that are in other than dwelling units and are likely to require examination, adjustment, servicing, or maintenance while energized shall be field marked to warn qualified persons of potential electric arc-flash hazards. The marking shall be permanently affixed to the equipment or wiring method, and be of sufficient durability to withstand the environment involved. The label shall adequately warn of the hazard using effective words, colors, and/or symbols. It should be located so it is clearly visible to qualified persons before examination, adjustment, servicing, or maintenance of the equipment.
- Both the NEC, in Section 110.16, and the NFPA 70E require that equipment be field or factory marked with a label which warns qualified persons of potential arc-flash hazards. The label includes information to warn of conditions such as the Flash Hazard Boundary, the arc-flash energy (expressed in cal/cm2), and the recommended PPE level. An example of this type of label is shown in Figure 1.
- /
- Figure 1Example of an Arc-Flash Warning Label, per NFPA 70E
- Electrically Safe Work Condition
- Both OSHA standards and NFPA 70E require that equipment be placed in an electrically safe work condition before employees work on or near them. Essentially, this requires that equipment be de-energized and that verification be made that the equipment is truly de-energized before it is worked on. There are exceptions for cases in which de-energizing would introduce additional hazards or for cases in which the work cannot be done with the system de-energized. For example, to shut down a life-support system or a ventilation system for a hazardous location would introduce additional hazard. Trouble shooting might be an example of work that cannot be done with the system de-energized.
- The point is that the basic requirement, and it is a requirement, is to de-energize before working on equipment. The reason is that the hazard is removed by de-energizing. With careful planning, work can almost always be done with equipment de-energized.
- However, placing equipment in an electrically safe work condition involves the main steps in which an electrical conductor or circuit part has been disconnected from energized parts, locked/tagged in accordance with established standards, tested to ensure the absence of voltage, and grounded if determined necessary.
- These steps are done while the equipment is not yet verified to be in a safe condition, which requires that appropriate protective precautions including use of PPE are applied during the de-energizing process.
- Electrical Safety Program
- NFPA 70E requires establishment of an electrical safety program for each facility. The safety program provides for developing practices, providing training for employees and performance of a flash hazard analysis. It is the responsibility of the employer to provide the practices and training. In addition, the employer is responsible to make sure that qualified employees are in compliance with safety-related practices, that re-training is conducted as needed, and that records of the employee training are documented. The employee is responsible for implementing the practices according to the training.
- OSHA requires that employers must estimate the incident heat energy of any electric-arc hazard to which a worker would be exposed. In addition, employers generally must provide workers exposed to hazards from electric arcs with protective clothing and other PPE with an arc rating greater than or equal to the estimated heat energy.
- Arc-Flash Risk Assessment
- Prior to working on energized equipment, including working through de-energizing steps, NFPA 70E-2015 requires that an arc-flash risk assessment be performed. The assessment is required to determine 1) the arc-flash boundary distance and 2) the type of PPE required for work on each piece of equipment. In order to establish these requirements either an incident energy calculation is generally necessary, or information in tables from NFPA 70E may be used.
- 4 Incident Energy Calculations
- The arc flash boundary shall be the distance at which the incident energy equals 1.2 cal/cm2 (5 J/cm2), according to NFPA 70E-2015. One of the units used to measure incident energy is calories per centimeter squared (cal/cm2).
- Incident Energy is defined in NFPA 70E-2015 as “The amount of thermal energy impressed on a surface, a certain distance from the source, generated during an electrical arc event.”
- The Incident Energy may be determined by using calculation derived from IEEE 1584, IEEE Guide for Performing Arc-Flash Hazard Calculations.
- IEEE 1584 provides the ability to perform calculations that more accurately take into consideration the true electrical conditions of the facility. These calculations are derived from the results of a significant volume of actual testing.
- 5 NFPA 70E Tables
- Depending on the type of electrical equipment, the arc-flash boundary and the associated PPE categories may also be determined by using tables of Arc-Flash Hazard PPE Categories found in NFPA 70E.
- NFPA 70E does not specifically require or exclude any method of assessment. Tables and guidelines exist in NFPA 70E that provide information to perform the assessment. The tables given in NFPA 70E provides a relatively simple approach which may be satisfactory when time and capability to perform more focused analysis are not available.
- Summary
- An arc flash is a serious hazard that is potentially devastating to those exposed to it. The requirements of NFPA 70E can be an aid to workers who are exposed to electricity. This is done by providing them with an understanding of how to reduce the probability of an arc-flash event and the devastating effect from one. OSHA assures the enforcement of safe working conditions, compliance to standards, and the availability of training materials. Compliance with these requirements will support the goal of reducing injuries and downtime of electrical systems.
- § [Go to Page]