The basics of arc flash mitigation

Electrical engineers must understand the codes, standards, and design requirements when engineering for arc flash mitigation.

08/15/2017


Learning objectives: 

  • Know that arc flash maintenance and design mitigation are paramount to electrical safety.
  • Understand NFPA 70: National Electrical Code and other codes or standards related to arc flash mitigation design.
  • Learn design tactics that will mitigate arc flash incidents.

An arc flash is an explosion of light, heat, and energy caused by the shorting of electrical connections, which poses as a serious hazard when working on electrical equipment. An arc flash occurrence can happen as a result of personnel mistakes or as a result of equipment or connection failure.

Figure 1: This image shows a breaker panel in which the arc flash hazard is clearly labeled to warn personnel of potential danger. Courtesy: RTM ConsultantsMany factors go into mitigating the danger that electrical workers face; engineers must thoughtfully design systems to reduce and mitigate these incidents in the field. Owners, facility managers, engineers, and contractors can all contribute to providing a safer place for personnel to work. The process all starts with safe equipment and engineering design, followed by proper installation of equipment and proper training and maintenance procedures.

Maintenance mitigation and design mitigation will be covered in this article, and an overview of the national codes and standards that pertain to arc flash. This holistic approach is intended to keep the best interests of all parties at hand while making personnel safety paramount.

Codes and standards

Before diving into the implementation techniques, it's important to know what governs arc flash regulations. There are four publications that play a large role in arc flash regulations including NFPA, NESC, OSHA, and IEEE.

NFPA 70: National Electrical Code contains a section about arc flash hazard warnings, which states that it is required for electrical equipment to be field- or factory-marked to inform personnel of the risk in working on each individual piece of equipment. The NFPA 70 code specifically refers to its counterpart, NFPA 70E: Standard for Electrical Safety in the Workplace, to outline more detailed requirements for arc flash safety. NFPA 70E outlines many of the arc flash requirements in more detail including arc flash risk assessments, arc flash boundaries, arc flash personal protective equipment (PPE), and electrical equipment labeling.

National Electrical Safety Code (NESC) also outlines arc flash regulations including arc flash hazard analysis to be completed before maintenance is performed on live equipment within certain voltage thresholds above exposure levels greater than 2 cal/cm2.

OSHA also recently added new regulations on arc flash safety. This evolution in regulations defines requirements for arc flash studies being performed. OSHA also outlines the use of PPE when working on and around exposed energized parts.

Lastly, the IEEE Standard 1584 outlines the specification of scope and deliverable requirements for an arc flash hazard calculation. This guide is extremely important in outlining the steps, from beginning an arc flash study and collecting data to making assumptions on unknown data, executing a study, and completing the equipment-labeling process.

These guidelines are the foundation for designing, installing, and maintaining electrical equipment safely while mitigating risk and exposure to the dangers of arc flash incidents.

Arc flash studies, labeling

The prime way to mitigate arc flash incidents is to ensure the facility has recently conducted a study, labeled equipment, noted zones, and trained facility staff in maintenance procedures. NFPA 70E outlines when a study must be conducted and for which types of equipment. Once the proper arc flash study has been performed, the overall system can be analyzed and the incident energy levels at each piece of equipment can be reviewed. At that time, it's important to determine whether modifications need to be made to the system to reduce dangerous incident energy levels.

The next step after any potential system modifications are made is to properly label each piece of equipment to identify its hazard level. The four levels of arch flash hazard range from one (least hazardous) to four (requiring personnel to wear full arc flash suits). Refer to Table 1 for a full description of each arc flash level.Table 1: This table identifies each of the hazard levels of arc flash incident, ranging from one to four. Courtesy: RTM Engineering Consultants.

Although it is important to properly label equipment, there also should be arc flash hazard warnings marked on the floor of any areas of danger. It's important to understand that distance greatly reduces the incident energy of arc fault, but knowing and understanding these boundaries will help to keep personnel who are not working on equipment safe while informing and educating them on the limits of arc flash areas.

Two additional maintenance factors that are crucial to be considered are the tightening of equipment conductor connections and the review of old and deteriorating conductors. Over time, conductors can become loose as a result of vibrations and thermal changes. Conductors that are not properly torqued are a prime hazard for arc flash occurrences. They should be regularly inspected and torqued to assure proper connection and to reduce arcing.

The second and potentially more serious factor concerns the degradation of conductor insulation. While torqueing a conductor can be completed in a routine and cost-effective manner, replacing old conductors can be costly and difficult. This poses an obvious challenge and can result in conductors being left in operation longer than their anticipated lifespan. Insulation provides a false sense of security when cracking and degradation can begin to expose energized parts of the conductor.


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