Shock & Arc Flash Approach Boundaries
Limited, restricted, and arc flash boundaries - distances, voltage tables, working distance, and boundary requirements for exposed energized parts.
- Define the purpose of approach boundaries in NFPA 70E
- Distinguish between limited, restricted, and arc flash boundaries
- Identify boundary distances for common voltage levels
- Explain the concept of working distance in arc flash analysis
- Describe who may enter each boundary and what protection is required
Leçon 1
Understanding Approach Boundaries
Why Boundaries Exist
NFPA 70E establishes approach boundaries around exposed energized electrical conductors and circuit parts. The purpose of these boundaries is to reduce shock risk by limiting access to areas where electrical hazards exist. Each boundary defines a distance from exposed live parts where specific protective measures are required.
Think of boundaries as concentric zones of increasing danger. As you move closer to exposed energized parts, the risk increases and the required protections become more stringent.
Exam Tip
The exam will ask about the purpose of approach boundaries. The answer is always to reduce shock risk by limiting access - not to specify conductor size, set torque values, or set breaker sizes.
The Three Boundary Types
NFPA 70E defines three primary boundaries:
- Arc Flash Boundary - the distance where incident energy reaches 1.2 cal/cm^2 (onset of second-degree burn). Anyone inside this boundary must wear arc-rated PPE.
- Limited Approach Boundary - the shock protection distance for exposed energized parts. Unqualified persons may not cross this boundary without escort by a qualified person.
- Restricted Approach Boundary - a closer shock boundary requiring insulated tools and additional protection. Only qualified persons with proper PPE may enter.
Arc Flash Boundary
Hazard: Arc flash (thermal burn)
Threshold: 1.2 cal/cm^2
Requires: Arc-rated PPE per incident energy or PPE category
Who enters: Only with arc-rated PPE
Limited Approach
Hazard: Electric shock
Threshold: Per voltage table
Requires: Shock hazard awareness
Who enters: Qualified persons; unqualified only if escorted
Restricted Approach
Hazard: Electric shock (higher risk)
Threshold: Per voltage table (closer)
Requires: Insulated tools, additional shock protection
Who enters: Qualified persons only with full protection
Approach boundaries exist to reduce shock risk by limiting access to energized parts. The three boundaries - arc flash, limited approach, and restricted approach - each define increasing levels of protection as you get closer to the hazard.