Limited and restricted approach boundaries differ from the arc flash boundary. The limited and restricted approach boundaries relate to electric shock hazards whereas the arc flash boundary is all about an arc flash hazard.

Understanding the differences between limited and restricted approach boundaries and the arc flash boundary is crucial for maintaining safety in environments where electrical hazards are present. These concepts are integral to the standards set forth by the National Fire Protection Association (NFPA), particularly NFPA 70E, which deals with electrical safety in the workplace.

Limited and Restricted Approach Boundaries

These boundaries are established to protect against electric shock, which is one of the most immediate risks when working near or with electrical equipment.

The Limited Approach Boundary is a boundary around exposed live parts within which a shock hazard exists. Personnel should not cross this boundary without appropriate personal protective equipment (PPE) and proper electrical safety training. The exact distance defining this boundary depends on the voltage of the electrical equipment and other situational factors.

The Restricted Approach Boundary is closer to live parts than the limited boundary. This area poses a greater risk for shock and electrical arc. Crossing into the restricted approach boundary is typically reserved for qualified personnel who have specific training to work at close distances to live electrical parts. These workers must use PPE and adhere to precise work procedures to mitigate risks.

Arc Flash Boundary

Unlike the limited and restricted approach boundaries, the arc flash boundary pertains to the risk of arc flash—a dangerous condition associated with the release of energy caused by an electrical arc.

The Arc Flash Boundary is the distance from exposed live parts within which a person could receive a second-degree burn if an arc flash were to occur. The size of the arc flash boundary is determined based on the potential energy of an arc flash at that location, which in turn depends on the electrical system's configuration, the fault current available, and the clearing time of the overcurrent protective devices. Safety measures for personnel within this boundary include wearing appropriate flame-resistant clothing and other PPE designed to protect against the thermal effects of an arc flash.

Summary

• Electric Shock Hazards: Managed through limited and restricted approach boundaries, focusing on preventing contact with live electrical components.
• Arc Flash Hazards: Addressed by the arc flash boundary, focusing on the potential exposure to explosive energy releases during an electrical fault.

The following definitions can be found in Article 100 of NFPA 70E:

Below is a sample of NFPA 70E. For the complete section, see the actual NFPA 70E text at NFPA.ORG. Once there, click on the free access link to NFPA 70E.

Boundary, Limited Approach (Limited Approach Boundary). An approach limit at a distance from an exposed energized electrical conductor or circuit part within which an electric shock hazard exists.

Boundary, Restricted Approach (Restricted Approach Boundary). An approach limit at a distance from an exposed energized electrical conductor or circuit part within which there is an increased likelihood of electric shock, due to electrical arc-over combined with inadvertent movement.