Arc Flash on Power Systems Rated 240 V and Below

I field a number of questions related to electrical codes, equipment design, and electrical hazards.  This month I had a number of questions related to the arc flash hazard requirements for equipment rated 240 V and below.  There is also a question related to this on the NFPA 70E group on LinkedIn.

Guidance for electrical safety comes from three standards:

• General Industry Safety Standards (OSHA 29 CFR 1910)
• Standard for Electrical Safety in the Workplace (NFPA 70E)
• IEEE Guide for Performing Arc-Flash Hazard Calculations (IEEE 1584)

OSHA standards require that employees be protected from reasonable and foreseeable hazards.  Foreseeable hazards include shock hazards and arcing hazards (arc flash and arc blast).  Protection from electrical hazards is required whenever people are working on or near any electrical systems of 50 V or greater [1].

The need for protection from shock hazards when working on exposed live (energized) electrical systems where the voltage is 50 V or greater is well defined in standards and research papers.  The need for protection from arcing hazards is understood when working on or near electrical systems above 240 V.  For electrical systems rated 240 V and below, the need and type of protection from arcing hazards are not well defined or understood.

Common questions when people are going to be working on or near an electrical system rated 240 V below include:

• Does an arc flash hazard analysis need to be completed?
• Do employees need to be concerned with arcing hazards?
• What type of PPE do employees need to wear?
• Can I use the Table 130.7(C)(15) and Table 130.7(C)(16) in NFPA 70E?
• Is there an exemption for single-phase sources fed by a 125 kVA transformer or less?

Before we can answer the questions, we need some background information on IEEE 1584 and NFPA 70E.  IEEE 1584 is the primary guide on performing an analysis of arcing hazards for an electrical system.  The IEEE working group that developed this guide and is in-charge of the activities around IEEE 1584 has reviewed various research papers, test procedures, data and have come to a consensus on calculating the incident energies, arc flash boundaries, and other parameters associated with arcing hazards.  IEEE 1584 covers three-phase electrical systems from 208 V to 15 kV [2].  Single-phase alternating current (AC) and all direct current (DC) systems are not included [2].  Using the equations in IEEE 1584 for systems lower than 208 V or for single phase systems can be used, but will result in conservative incident energy calculations and arc flash boundaries [2].

NFPA 70E is the primary US standard that is used to address all electrical hazards in the workplace.  This includes setting up processes, training of employees, determining protection boundaries, personnel protective equipment (PPE) requirements, etc.  The requirements for arc flash hazard analyses are just one section of the NFPA 70E standard.

I believe that the confusion taking place today is a result of an understanding of the requirements and the standards available, and how standards have changed over time – specifically NFPA 70E.

The latest version of NFPA 70E (2012 edition), Article 130.5 requires an arc flash hazard analysis of an electrical system [3].  NFPA 70E uses IEEE 1584 as the basis for all of calculations related to arcing hazards [3].  An exemption is provided that allows for the use of Table 130.7(C)(15) and Table 130.7(C)(16) to be used in lieu of the arc flash hazard analysis [3].  Informational Note 5 refers the user of the standard to IEEE 1584 for three-phase systems rated 240 V or less [3].  While this may seem clear, it is not.

In the 2009 edition of NFPA 70E, there was clear guidance on systems rated 240 V or below.  If the system was from a single-phase source, and fed from a transformer rated not more than 125 kVA, then an arc flash hazard analysis was not required [4].  While this requirement does not require an arc flash hazard analysis, it does not remove the requirement that people working on near exposed live (energized) circuits rated 50 V or greater be protected.

Based on the requirements from OSHA and NFPA [1,3], the following recommendations should be considered when working on or near exposed live (energized) circuits rated 50 V or greater:

• Conduct a comprehensive arc flash hazard analysis for all equipment
• Use the Table 130.7(C)(15) for shock hazards
• Use NFPA 70E Table 130.7(C)(16) for arcing hazards when the voltage 240 V or less
• A software program (EasyPower or SKM) can also be used, but conservative values will be obtained
• Hazard warning labels should be provided on all electrical equipment where people could be exposed to the energized circuits according to NFPA 70E [3]
• Include shock hazards
• Include arcing hazards (arc flash)
• Ensure safe working practices are used
• Ensure safe working boundaries are established
• Ensure PPE is used properly

On another notes, the numbers of user of the Day-One-Safety checklist continues to grow.  This tool will help your employees be safe.

If you are unfamiliar with the Day-One-Safety checklist, this software application is intended to assist people with working in new or unfamiliar facilities or locations.  This is a free on-line checklist available to anyone who wants would like to use it.  To request a password send me an email at cole3250@gmail.com or to Login, click here.

References:

1. Occupational Safety and Health Administration (OSHA), General Industry Safety Standards, OSHA 29 CFR 1910
2. Institute of Electrical and Electronic Engineers (IEEE), IEEE Guide for Performing Arc-Flash Hazard Calculations, IEEE 1584:2002.  Piscataway, NJ USA
3. National Fire Protection Association (NFPA), Standard for Electrical Safety in the Workplace, NFPA 70E-2012.  Quincy, MA USA
4. National Fire Protection Association (NFPA), Standard for Electrical Safety in the Workplace, NFPA 70E-2009.  Quincy, MA USA