NFPA 70E doesn't draw one line around energized equipment - it draws several, and each one answers a different question. Getting the order right, and knowing which rule applies at which distance, is one of the highest-frequency topics on the exam.
Limited Approach Boundary - the fence for unqualified workers
This is the outermost line that matters for someone who isn't a qualified electrical worker. An unqualified person can cross it only if continuously supervised by a qualified person, and only under specific conditions. Think of it as the point where "just walking by" ends and "now you're in the work area" begins.
Restricted Approach Boundary - qualified persons only
Closer in, shock risk becomes significant enough that only qualified persons may enter - and entering requires appropriate shock PPE, a written plan for the task, and treating the exposed conductors as if accidental contact were a real, live possibility. This boundary roughly tracks the distance at which an accidental slip could mean actual contact.
Arc Flash Protection Boundary - calculated, not fixed
Unlike the shock boundaries, this one is calculated from incident energy, not set by a fixed distance rule. It marks the distance at which someone without adequate arc-rated PPE would receive a second-degree burn (NFPA 70E uses 1.2 cal/cm² as that threshold). Depending on the system, this boundary can land inside or outside the shock boundaries - at lower voltages it may sit closer in, while at medium or high voltages it can extend several feet out. That's calculated during the arc flash study and printed directly on the equipment's arc flash label.
Putting the order together
From the outside in: Arc Flash Protection Boundary is often the outermost perimeter, then the Limited boundary, then the Restricted boundary, and finally direct contact with the equipment itself (the prohibited zone). But because the Arc Flash boundary is calculated independently of the shock boundaries, they don't always nest the way you'd expect - it's entirely possible to be outside the Limited Approach Boundary but still inside the Arc Flash Protection Boundary, which means arc-rated PPE is required even though shock PPE technically isn't yet.
One more number worth knowing: NFPA 70E's shock protection requirements activate at 50V and above. Below that, bare conductors generally aren't treated as a shock hazard - though arc flash risk can still exist depending on available fault current.
Full boundary definitions and worked scenario questions are in the Study Guide and the Exam Companion.
Standard reference: NFPA 70E 2024.