Limited Approach Boundary Defined
The Limited Approach Boundary defines the distance from energized parts where shock protection becomes mandatory. Based on system voltage, this NFPA 70E-defined zone determines when PPE, qualified supervision, and safety planning are required for safe electrical work.
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What Is the Limited Approach Boundary?
The Limited Approach Boundary is a shock protection zone set at a specific distance from an exposed energized part. It is designed to limit the likelihood of accidental contact or electrical arc-related shock when performing tasks near energized components.
This boundary is not about thermal energy like the Arc Flash Boundary but focuses on voltage potential and human proximity. If you cross this line, you enter an area with an increased risk of electric shock.
How Is It Determined?
The Limited Approach Boundary is based on system voltage. For example:
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50V to 150V: 3 feet, 6 inches (1.07 meters)
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151V to 750V: 3 feet, 6 inches (1.07 meters)
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751V to 15kV: 5 feet (1.52 meters)
For detailed comparisons of voltage thresholds and distances, see our Arc Flash Boundary Table by Incident Energy.
These distances are determined using standardized shock hazard equations and are listed in NFPA 70E Annex C.
Practical Workplace Implications
Crossing the Limited Approach Boundary isn't prohibited — but it triggers specific safety requirements:
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Only qualified personnel may cross unaccompanied
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A qualified person must continuously escort unqualified workers
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A shock risk assessment must be completed beforehand
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Workers must wear appropriate voltage-rated gloves and tools
This boundary often defines the start of the decision-making zone — where PPE becomes mandatory and Lockout/Tagout protocols must be in place.
If work is to be performed closer than this boundary, it often overlaps with or leads into the Restricted Approach Boundary, which involves even stricter controls.
Limited vs Arc Flash Boundary
It’s common to confuse the Limited Approach Boundary with the Arc Flash Boundary. Here’s how they differ:
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Limited Approach Boundary: Focuses on shock hazards, measured by voltage
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Arc Flash Boundary: Focuses on thermal hazards, measured in cal/cm²
Both can exist in the same workspace but are based on separate risk types. For a full breakdown, visit our guide on What Is an Arc Flash Boundary.
Related Safety Zones
Understanding where the Limited Approach Boundary sits in context can help clarify the full protective strategy. These include:
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Restricted Approach Boundary: Tighter zone requiring insulated tools and elevated qualifications
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Prohibited Approach Boundary: Now deprecated, once treated as equivalent to direct contact
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Arc Flash Boundary Chart: Visual aid comparing all boundary distances
Each plays a role in defining the total safe working environment.
Training and Labeling Requirements
Electrical equipment must be labeled to indicate all applicable boundaries, including the Limited Approach Boundary. Workers should receive training through certified programs that teach how to identify, assess, and respond to these shock protection zones. Our Arc Flash Boundary Calculation page explains how these distances are determined.
For workplace-specific assessments, use the 8-cal/cm² PPE threshold example outlined in our Arc Flash Boundary for 8 cal/cm² page.
Related Pages
Arc Flash Boundary Table By Incident Energy
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