Environmental, Health and Safety Services

Approach Boundaries

As part of the risk assessment process, approach boundaries should be determined. There are two shock protection boundaries; the Limited Approach Boundary (LAB) and the Restricted Approach Boundary (RAB), and one Arc Flash Boundary (AFB) that must be established in order to provide a safe distance for personnel from exposed, energized electrical components.

Limited Approach Boundary

The Limited Approach Boundary (LAB) is the approach distance to exposed, energized electrical components within which a shock hazard exists. It is the approach limit for unqualified persons. Unqualified persons may only cross this boundary if they are under the direct supervision of a qualified person, and wearing the appropriate personal protective equipment for the hazards involved. Working within the LAB is only acceptable if an Energized Electrical Work Assessment has been completed and approved, or if the work is specifically exempt per NFPA 70E-2015 130.2(B)(3).

The LAB is determined by selecting the voltage range and exposed conductor/circuit condition (i.e. either movable or fixed, column 2 or 3) in NFPA 70E-2015 Table 130.4(D)(a) for alternating current. Use NFPA 70E-2015 Table 130.4(D)(b) for direct current.

Restricted Approach Boundary

The Restricted Approach Boundary (RAB) is the approach limit for qualified persons to exposed, energized electrical components where there is an increased likelihood of electric shock due to electrical arc-over combined with inadvertent movement. Only qualified persons may cross this boundary. A qualified person required to cross the RAB must be protected from unexpected contact with exposed energized conductors or circuit parts. Working within the RAB is only acceptable if an Energized Electrical Work Assessment has been completed and approved, or if the work is specifically exempt per NFPA 70E-2015 130.2(B)(3).

The RAB is determined by selecting the voltage range in NFPA 70E-2015 Table 130.4(D)(a) for alternating current (column 4). Use NFPA 70E-2015 Table 130.4(D)(b) for direct current.

Prohibited Approach Boundary

The Prohibited Approach Boundary (PAB) was used in earlier versions of NFPA 70E, but is no longer referenced in the current version. The term, however, may still be used in electrical research applications. The PAB is the approach distance for qualified persons to exposed live parts within which work is considered the same as making contact with the live part.

The PAB is determined by selecting the voltage range in NFPA 70E-2012 Table 130.2(C) for alternating current.

Arc Flash Boundary

The Arc Flash Boundary (AFB) is the distance from exposed, energized electrical components within which a person could receive a second degree burn if an electrical arc flash were to occur. The AFB is determined either through calculation or through the use of the following tables. Personnel must be wearing the appropriate arc-rated protective equipment before crossing this boundary. Arc-rating is reported as either the Arc Thermal Performance Value (ATPV) or the Energy of Break-open Threshold (EBT).

In order to determine if arc flash protective equipment is required for a given task, review NFPA 70E-2015 Table 130.7(C)(15(A)(a) for alternating and direct current systems for typical or traditional electrical exposures, or use the calculation method recommended by IEEE Std 1584a under engineering supervisor to determine the boundary. If the system meets the following criteria, an AFB of 4 feet may be used:

  • The available bolted fault current does not exceed 50 kA and the clearing time of the circuit protective device does not exceed 2 cycles, or
  • The product of the bolted fault current and clearing time does not exceed 100 kA-cycles.

The AFB can then be determined by selecting the relative work task from NFPA 70E-2015 Table 130.7(C)(15)(A)(b) for alternating current or Table 130.7(C)(15)(B) for direct current systems.

Note: Tables and charts referenced here are provided to personnel during Electrical Qualified Person training, or by contacting EHS for more information.