NFPA 70E Arc flash table: Detailed Guide

NFPA 70E Arc flash table

Evolution of the tables

The evolution of the arc-flash Personal Protective Equipment (PPE) table within the NFPA 70E Standard for Electrical Safety in the Workplace reflects a continual effort to improve workplace safety by providing clearer, more practical guidelines for the selection of arc-rated clothing and PPE. Here’s an overview of its development over the years:

Initial Introduction and Early Changes

2000 Edition: The NFPA 70E standard began including task tables as a method to guide the selection of arc-rated clothing and PPE. This was in response to the need for a practical solution for workers in the absence of an incident energy analysis. These early tables provided a simplified approach but were often criticized for being difficult to apply in the field and for the arbitrary reduction of Hazard/Risk Category (HRC) numbers based on perceived risk.

Read More: NFPA 70E Compliance and Electrical Safety Standards

Refinements for Clarity and Usability

Subsequent Editions (2004, 2009, 2012): Over the years, the NFPA 70E committee made revisions to the tables to address feedback from the field. These revisions aimed at making the tables more user-friendly and reducing the ambiguity in selecting appropriate PPE. Adjustments were made to clarify the criteria for different the hazard level/risk categories and to refine the guidelines for when certain types of PPE should be used.

Major Overhaul for Enhanced Safety

2015 Edition: Significant changes were made to the table method, drawing from lessons learned and advancements in safety research. The emphasis shifted towards a more comprehensive risk assessment approach, with the tables serving as a critical tool to supplement the assessment rather than being the sole determinant of PPE selection. This edition sought to balance the need for practical, field-applicable guidance with the complexity of accurately assessing arc flash risks.

Simplification and Integration

2018 Edition table two: The most recent updates focused on simplifying the table method by reducing the number of tables and integrating them more closely with the incident energy analysis method. This edition introduced three main tables:

Table 130.5(C): Assists in determining the likelihood of arc flash occurrence, emphasizing the point that this table is not a substitute for a full risk assessment.

Tables 130.7(C)(15)(a), (b), and (c): Provide guidelines for selecting arc-rated clothing and PPE based on specific task conditions and system parameters. The changes aimed at eliminating the perceived risk reductions and ensuring that if a PPE category is mandated by the table method, full protection is specified.

Current Focus and Future Directions

The evolution of the NFPA 70E arc-flash PPE tables reflects a shift towards more data-driven, risk-assessment-based approaches to safety. It underscores the importance of incident energy analysis while providing practical, field-applicable guidance for situations where such analysis has not been performed. The NFPA 70E committee continues to incorporate feedback from industry professionals and advances in safety research to enhance the utility, accuracy, and effectiveness of these tables.

Fault current and clearing time

The magnitude of the fault current is a critical factor in determining the severity of an arc flash. A higher fault current can lead to a more intense arc flash, with greater energy release and potential for harm. The available fault current depends on the configuration and capacity of the power system, including the ratings of transformers, the impedance of the connections, and the layout of the electrical network.

The clearing time of protective device is a crucial component in the calculation of incident energy for an arc flash hazard analysis. Shorter clearing times result in less energy being released during an arc flash fault incident, thereby reducing the potential for injury and damage. The clearing time depends on the characteristics and settings of the protective devices in the electrical system.

What is the Table Method of NFPA 70E

The NFPA 70E, “Standard for Electrical Safety in the Workplace,” specifies requirements for arc flash labeling to improve safety and awareness around electrical equipment susceptible to arc flash hazards. These labels are critical for informing workers about the potential risks involved in working with or near electrical equipment and specifying the necessary personal protective equipment (PPE) and safety measures. Here’s an overview of the arc flash label requirements as outlined in NFPA 70E:

table for ac current system
table for ac current system

General Requirements for Arc Flash Labels

  • Presence of Labels: Electrical equipment such as switchboards, panelboards, industrial control panels, meter socket enclosures, and motor control centers that are likely to require examination, adjustment, servicing, or maintenance while energized must be marked with an arc flash label.
  • Content of Labels: The label must include at least the following information:
    1. Nominal system voltage
    2. Arc flash boundary
    3. At least one of the following:
      • Available incident energy and the corresponding working distance
      • Minimum arc rating of clothing
      • Arc flash PPE category (from NFPA 70E tables)
      • Highest Hazard/Risk Category (HRC) for the equipment
  • Method of Calculating Incident Energy: The label should indicate the incident energy or required level of PPE based on a detailed arc flash risk assessment. This can involve calculations following the NFPA 70E guidelines or using the NFPA 70E PPE categorization tables if a detailed analysis is not performed.
  • Additional Information: While not mandatory, labels often include other pertinent information such as the date of the last hazard analysis, and specific PPE required, to provide clear guidance to personnel working on or near the equipment.

What is the NFPA 70E arc flash label requirement?

The NFPA 70E arc flash label requirements are designed to communicate essential safety information to personnel working on or near electrical equipment, specifically regarding the potential hazards of arc flash incidents given electrical situation. These labels are a critical component of workplace electrical safety, helping to ensure that workers are aware of the risks and the necessary and appropriate personal protective equipment and measures when interacting with electrical systems. Below is a detailed outline of the arc flash label requirements as per the most recent editions of NFPA 70E:

 

What is the arc flash boundary of NFPA 70E?

arc flash boundary

NFPA 70E Table 130.7(C)(15)(b): PPE Categories for DC Systems

Here, you’ll find a list of DC equipment and their parameters, along with the corresponding arc flash boundary and the category of arc flash personal protective equipment (PPE) that applies.

NFPA 70E Table 130.7(C)(15)(b): PPE Categories for DC Systems

Notes

Clothing likely to come into contact with electrolytes must satisfy the following two criteria:

  1. Undergo an assessment for electrolyte protection.
  2. Be arc-rated.

*Note for clarification: ASTM F1296, which is a Standard Guide for Evaluating Chemical Protective Clothing, provides details on assessing clothing for electrolyte protection.

**Additional Note: ASTM F1891, outlining the Standard Specifications for Arc Rated and Flame Resistant Rainwear, offers guidelines for evaluating arc-rated clothing.

In situations where there isn’t an overcurrent protective device (OCPD) present, or if the fault clearing time is unknown, a two-second arc duration is presumed. However, if the fault clearing time is known and it’s less than two seconds, performing an incident energy analysis may yield a more accurate reflection of the potential danger.

Informational Note 1: It’s important to consider the impact of cables and any other circuit impedances when calculating available fault current. The most accurate approach to ascertain the available short-circuit current at the arc point is through power system modeling. Battery cell short-circuit currents can typically be acquired from the battery manufacturer. Refer to Informative Annex D.5 for foundational table values and alternative methods for determining DC incident energy, which should be applied using sound engineering judgment.

Informational Note 2: The methods employed to estimate DC arc-flash incident energy for this table’s categories are derived from open-air incident energy calculations. This approach was chosen because many battery systems and other DC processes are situated in open spaces or rooms. If the specific task is inside an enclosure, it might be wise to consider additional PPE protection than what is indicated in this table. Studies involving AC arc flash have revealed that being in an enclosure could increase the risk up to three times compared to open air. Therefore, applying engineering judgment is essential when considering the specific equipment conditions and the task at hand.

NFPA 70E Table 130.7(C)(15)(a): PPE Categories for AC Systems

table for ac current system
table for ac current system

Core Information Required on Arc Flash Labels

Arc flash labels must include specific information to adequately warn and inform workers about the potential arc flash hazards associated with electrical equipment. This information generally includes the essential information:

  1. Nominal System Voltage: Indicates the voltage level of the electrical system or equipment.
  2. Arc Flash Boundary: The distance from the equipment within which a person could receive a second-degree burn if an arc flash were to occur. This boundary is critical for determining safe working distances.
  3. At least one of the following:
    • Incident Energy: Expressed in calories per square centimeter (cal/cm²), this value represents the energy exposure at a specified working distance and is used to determine the appropriate level of PPE.
    • Arc Flash PPE Category: A number from 1 to 4 (with 4 being the highest risk) that corresponds to a specific category of PPE required. This category is based on the tables provided in NFPA 70E if the incident energy analysis is not performed.
    • Minimum Arc Rating of Clothing: Indicates the minimum arc rating for PPE, in cal/cm², that must be worn to protect against the arc flash hazard.
    • Alternatively, the label can specify the required level of PPE directly, based on the results of the arc flash risk assessment.

What is the arc flash table method?

The method revolves around the use of tables that categorize various electrical tasks and the corresponding PPE required based on general conditions. These tables consider factors like the task to be performed, the equipment involved, and its operating condition. The method aims to make it easier for employers and workers to quickly identify the level of protection needed under typical circumstances.

 

Key Components

  1. Task-Specific Guidelines: Tables identify common electrical tasks and specify the arc flash PPE category or minimum arc rating of clothing needed for protection. Tasks are categorized based on the risk they pose and the conditions under which they are performed.
  2. Equipment Categories: The tables also consider the type of electrical equipment being worked on, such as switchboards, panelboards, motor control centers, and others. The categorization helps in identifying the appropriate PPE based on the equipment’s characteristics and the work environment.
  3. PPE Categories: NFPA 70E outlines PPE Categories 1 through 4, with each category specifying a different level of protection based on the potential incident energy exposure. Each category is associated with specific types of arc-rated clothing and other protective gear necessary to mitigate the risk of injury from an arc flash.