Restricted Approach Boundary
The Restricted Approach Boundary (RAB) is the innermost shock protection boundary around exposed energized electrical conductors or circuit parts, within which there is an increased likelihood of electric shock due to arc-over combined with inadvertent movement. It may only be crossed by a qualified person using prescribed PPE, tools, and work controls, as defined by NFPA 70E and CSA Z462.
On a manufacturing shop floor, the RAB is applied through shock risk assessments for tasks near energized parts ≥50 V, using voltage-based tables (e.g., 151–750 V AC ~ 0.3 m). Unqualified personnel are never allowed to cross RAB. Qualified persons may cross only with a shock risk assessment, Energized Electrical Work Permit, voltage-rated rubber gloves, insulated tools, and arc-rated clothing. Physical controls like barricades and floor tape mark boundaries, and digital compliance systems (e.g., SafeDesk) enforce pre-task checklists and PPE verification, aligning with WorkSafeBC Part 19 limits of approach.
How is the Restricted Approach Boundary distance determined for typical shop voltages?
NFPA 70E and CSA Z462 provide tables of approach boundaries by nominal system voltage, separate for AC and DC. For example, 50–150 V AC: Limited ~3.0 m, Restricted ~1.0 m; 151–750 V AC: Limited ~3.0 m, Restricted ~1.0 m, Prohibited ~0.3 m. Facilities standardize default RAB values for common voltages (120/208/240/480/600 V) and embed them into procedures or digital systems.
What is the relationship between Arc Flash Boundary and Restricted Approach Boundary?
The Arc Flash Boundary (AFB) is a thermal boundary for second-degree burns, while the Restricted Approach Boundary (RAB) is a shock protection boundary. AFB can be greater than, less than, or equal to RAB depending on fault energy. Qualified workers must comply with both: arc-rated PPE inside AFB, and shock PPE and insulated tools inside RAB.
When is working inside the Restricted Approach Boundary considered acceptable?
Working inside RAB is acceptable only when an Energized Electrical Work Assessment determines de-energizing is not feasible or introduces greater risk, a formal Energized Electrical Work Permit is issued, a qualified person performs the work with documented training, and full shock and arc-flash PPE, insulated tools, and barriers are used. Work must be planned to avoid contact zones.