Safety Leader

Meeting Boundary Requirements: Defining and calculating LAB, RAB and AFB

Published On
May 13, 2022

Article 100 contains definitions that are essential to the proper application of NFPA 70E. Three separate boundaries are defined in this article. Two are shock protection boundaries—the limited approach boundary (LAB) and restricted approach boundary (RAB)—and the third is the arc flash boundary (AFB).

This article provides examples of how each of the boundaries triggers NFPA 70E requirements, but it does not contain every requirement.

Table 130.4(E)(a) provides the shock protection boundaries to exposed energized electrical conductors or circuit parts for AC systems. The LAB and RAB are measured from exposed energized electrical conductors or circuit parts.

Limited approach

The LAB (3 feet, 6 inches for 50V–750V AC) is defined as the distance from an exposed energized electrical conductor or circuit part within which a shock hazard exists.

The general rule for implementing an electrically safe work condition (ESWC) in Section 110.3 is based on the LAB trigger. Before employees perform work within the LAB—or where the employee interacts with the equipment where conductors and circuit parts are not exposed but an increased likelihood of injury from arc flash exists—an ESWC must be established. Qualified persons must be trained in accordance with Section 110.6.

Qualified persons permitted to work within the LAB must be trained in:

  • the skills and techniques to distinguish exposed energized conductors and circuit parts,

  • the skills and techniques necessary to determine nominal voltage,

  • the approach distances for the LAB and RAB and

  • the decision-making process to perform the necessary job safety planning, identification of electrical hazards, assessment of associated risk and selection of the appropriate risk control method from the hierarchy of control.

Section 130.4E requires that unqualified persons may not approach nearer than the LAB and to apply alerting methods to warn them of electrical hazards.

Restricted approach

The RAB (1 foot for 151V–750V AC) is defined as the distance from an exposed energized electrical conductor or circuit part within which there is an increased likelihood of electric shock, due to electric arc-over combined with inadvertent movement. The requirement for an energized electrical work permit (EEWP) in Section 130.2 is based upon the RAB trigger.

Before employees perform work within the RAB or where the employee interacts with the equipment where conductors and circuit parts are not exposed but an increased likelihood of injury from arc flash exists, an EEWP is required and must be documented. Section 130.4(G) requires that no qualified person approach or take any conductive object closer to exposed energized conductors or circuit parts than the RAB unless the qualified person is insulated or guarded from energized conductors or circuit parts. Where rubber insulating gloves and sleeves are used, they are considered insulation only with regard to the energized parts upon which work is performed. Section 130.7(D)(1) requires that tools and any other equipment used within the RAB be insulated.

Arc flash

Article 100 defines an arc flash hazard as a source of possible injury or damage associated with the release of energy caused by an electrical arc. The definition is technically accurate but does little to help the user understand when and where an arc flash hazard exists. Informational note No. 1 explains that an arc flash hazard exists under two conditions: (1) when energized electrical conductors or circuit parts are exposed and (2) when energized electrical conductors or circuit parts are guarded or enclosed, provided a person is interacting with the equipment in such a manner that could cause an electric arc. This means that an AFB exists only where there are exposed energized parts or a person is interacting with the equipment in a manner that increases the likelihood of an arc flash.

Section 130.5(E) provides two methods to determine the AFB. Where an incident energy analysis is performed, the AFB is the distance at which the incident energy equals 1.2 cal/cm2. Where the arc flash PPE category method is used, the AFB is determined by 130.7(C)(15). Section 130.7(C)(1) requires that all parts of the body inside the AFB be protected from arc flash. This requires arc-rated clothing and other protective equipment.

Where an incident energy analysis is performed, the user of the standard is permitted to apply Table 130.5(G) for arc-rated clothing and other PPE. Where the arc flash PPE category method is used, Table 130.7(C)(15)(c) is applied.

The requirements triggered by these boundaries are independent and also overlap. For example, when applying the arc flash PPE category method for work in a 480/277V panelboard, the arc flash boundary in Table 130.7(C)(15)(a) is 3 feet. The LAB is 3 feet, 6 inches and the RAB is 1 foot. While the trigger for insulating gloves and leather protectors is at 1 foot, the hands require protection from arc flash and shock, requiring that all PPE be worn by the qualified person crossing the AFB.

About the Author

Jim Dollard

Code Columnist

Jim Dollard is the safety coordinator for IBEW Local 98 in Philadelphia. He is a member of the NEC Correlating Committee, NEC CMP-10, NEC CMP-13, NFPA 70E, NFPA 90A/B and the UL Electrical Council. He can be reached at codefaqs@gmail.com.

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