Shock approach boundaries are invisible lines drawn around exposed energized conductors that define zones of increasing electrical shock hazard. Unlike arc flash boundaries, which protect against thermal energy, shock boundaries protect against direct contact with energized parts. NFPA 70E-2024 defines three approach boundaries — limited, restricted, and prohibited — each with specific requirements for who can cross them, what qualifications they must have, and what protective measures must be in place. These boundaries apply whenever exposed energized electrical conductors or circuit parts are present, regardless of whether an arc flash hazard also exists.
This guide explains the three shock approach boundaries, the NFPA 70E tables that define them, the practical requirements for crossing each boundary, and common misconceptions about how shock and arc flash boundaries relate to each other.
The Three Shock Approach Boundaries
NFPA 70E defines three concentric boundaries around exposed energized conductors or circuit parts. Each boundary is measured from the energized part outward, and each defines a zone with increasing hazard and more stringent requirements for entry.
The limited approach boundary is the outermost boundary. It is the distance from the energized part at which a shock hazard exists. Unqualified persons must not cross this boundary unless they are escorted by a qualified person and are continuously accompanied. The limited approach boundary has two values in the NFPA 70E tables: one for situations involving a movable conductor (such as a dangling wire or a flexible cord) and one for situations involving a fixed circuit part (such as a bus bar or terminal). The movable conductor distance is larger because a loose conductor can swing or be inadvertently moved into contact with a person.
The restricted approach boundary is the middle boundary. It is the distance from the energized part within which there is an increased risk of shock due to electrical arc-over combined with inadvertent movement. Only qualified persons may cross this boundary, and they must use insulated tools, wear appropriate shock protection (insulating gloves and sleeves rated for the voltage), and have an approved energized work permit or meet the exceptions for testing and diagnostics. The restricted boundary represents the minimum approach distance that accounts for the possibility of a worker accidentally moving closer while performing a task.
The prohibited approach boundary was present in earlier editions of NFPA 70E but was removed starting with the 2021 edition. In current editions, the concept is effectively merged into the restricted approach boundary requirements. Workers who must approach closer than the restricted approach boundary are considered to be working on energized parts and must comply with all requirements for energized electrical work, including PPE, work permits, and job briefings.
The prohibited approach boundary was removed in NFPA 70E-2021. Current editions use the limited and restricted approach boundaries. Work inside the restricted boundary is considered equivalent to direct contact with energized parts and requires full energized work procedures.
Shock Approach Boundary Calculator
Look up limited, restricted, and prohibited approach boundaries for shock protection per NFPA 70E Table 130.4(E)(a) for AC and (b) for DC. Visual boundary zone diagram included.
AC Shock Approach Boundaries
NFPA 70E-2024 Table 130.4(E)(a) provides shock approach boundary distances for AC systems. The table is organized by nominal system voltage and lists the limited approach boundary (for both movable conductors and fixed circuit parts) and the restricted approach boundary. The distances increase with voltage because higher voltages can arc across larger air gaps.
For common industrial voltages, the boundary distances are as follows. At 120V to 150V (typical branch circuits), the limited approach boundary is 3 ft 6 in (1.07 m) for movable conductors and 3 ft 6 in for fixed circuit parts, and the restricted approach boundary is "avoid contact." At 151V to 600V (typical 208V, 277V, 480V systems), the limited approach boundary is 3 ft 6 in (1.07 m) for movable conductors and 3 ft 6 in for fixed circuit parts, and the restricted approach boundary is 1 ft 0 in (305 mm). At 601V to 2,500V, the limited approach boundary increases to 4 ft 0 in for fixed parts and the restricted boundary is 2 ft 2 in.
At medium voltages — 2,501V to 15,000V (common for large motors, substations, and distribution feeders) — the boundary distances increase significantly. The limited approach boundary for fixed circuit parts ranges from 5 ft 0 in to 5 ft 8 in depending on the specific voltage within this range, and the restricted boundary ranges from 2 ft 7 in to 4 ft 3 in. At above 15 kV, boundary distances continue to increase and the tables provide values up to 800 kV for transmission-level voltages.
These distances are based on the electrical characteristics of air as an insulating medium and the expected body movement of a worker performing a task. They assume a standard atmospheric pressure at sea level. At high altitudes or in environments with reduced air density (such as hot, humid conditions), the breakdown voltage of air is lower and additional safety margin may be appropriate, though NFPA 70E does not provide altitude correction factors for shock boundaries.
At 480V — the most common industrial voltage — the limited approach boundary is 3 ft 6 in and the restricted approach boundary is 1 ft 0 in. These distances are smaller than many workers expect. In a crowded motor control center, a worker standing in front of an open bucket is already inside the limited approach boundary and may be at or inside the restricted approach boundary.
DC Shock Approach Boundaries
NFPA 70E-2024 Table 130.4(E)(b) provides shock approach boundary distances for DC systems. DC shock boundaries are particularly important for battery rooms, solar PV systems, DC bus bars in variable frequency drives, electric vehicle charging systems, and telecommunications power systems. With the growth of battery energy storage, data center DC distribution, and solar installations, DC shock boundaries are relevant to a growing number of workers.
The DC boundary distances generally follow the same pattern as AC — increasing with voltage — but the specific distances differ because DC arcs behave differently than AC arcs. A DC arc, once established, does not pass through a current zero every half-cycle as AC arcs do. This means DC arcs are harder to extinguish and can sustain across longer gaps than AC arcs at the same voltage. The DC boundary table accounts for this difference.
For 100V to 300V DC (typical battery banks, solar string voltages), the limited approach boundary is 3 ft 6 in for both movable conductors and fixed circuit parts, and the restricted approach boundary is 1 ft 0 in. For 301V to 1,000V DC (larger battery systems, higher-voltage solar arrays), the limited approach boundary is 5 ft 0 in and the restricted boundary is 3 ft 6 in. These distances are notably larger than the equivalent AC distances at the same voltage, reflecting the greater difficulty of interrupting DC arcs.
Workers in battery rooms and solar installations should be especially aware of DC shock boundaries. Battery terminals and bus bars in a large UPS or energy storage system can be at 400V to 600V DC or higher. Solar array combiners can have string voltages of 600V to 1,500V DC. These voltage levels produce boundary distances that extend well beyond arm's reach, meaning multiple workers in a battery room or combiner box area may simultaneously be inside the approach boundaries.
DC approach boundaries are generally larger than AC boundaries at the same voltage because DC arcs sustain more readily across gaps. A 600V DC battery bus has a larger restricted approach boundary than a 600V AC bus.
Shock Approach Boundary Calculator
Look up limited, restricted, and prohibited approach boundaries for shock protection per NFPA 70E Table 130.4(E)(a) for AC and (b) for DC. Visual boundary zone diagram included.
Who Can Cross Each Boundary and How
The rules for crossing approach boundaries are based on the person's qualification level and the protective measures in place. NFPA 70E defines a qualified person as one who has demonstrated skills and knowledge related to the construction and operation of electrical equipment and installations and has received safety training to identify and avoid the hazards involved. An unqualified person is anyone who does not meet this definition.
Outside the limited approach boundary: No restrictions. Anyone can work or walk in this area without electrical shock PPE or special qualifications. This is the "safe" zone from a shock perspective (though arc flash boundaries may extend further than shock boundaries at some equipment, requiring arc flash PPE in areas beyond the shock limited approach boundary).
Between the limited and restricted approach boundaries: Unqualified persons may enter this zone only if they are continuously escorted by a qualified person and are advised of the electrical hazards. The qualified escort must keep the unqualified person from approaching closer than the restricted approach boundary. Qualified persons may work in this zone with appropriate awareness of the hazard and must not bring conductive tools, equipment, or materials closer than the restricted approach boundary unless they are insulated or guarded.
Inside the restricted approach boundary: Only qualified persons may enter this zone. The worker must use insulating PPE (voltage-rated gloves and sleeves appropriate for the voltage), use insulated tools, and have an approved energized electrical work permit (or meet the exemptions for testing, diagnostics, or other tasks listed in NFPA 70E). Work inside the restricted approach boundary is considered equivalent to working on or near energized parts and triggers all of the energized electrical work requirements, including a job briefing, an energized work permit, and appropriate PPE for both shock and arc flash hazards.
Working inside the restricted approach boundary requires: (1) qualified person status, (2) voltage-rated insulating gloves and sleeves, (3) insulated tools, and (4) an energized work permit unless an exemption applies. All four elements must be in place simultaneously.
Shock Boundaries vs Arc Flash Boundaries
Shock boundaries and arc flash boundaries are independent hazard assessments. They protect against different types of injury (electrocution vs thermal burns), are calculated using different methods, and result in different distances. A common misconception is that the arc flash boundary and the shock limited approach boundary are the same thing or that one always encompasses the other. In reality, either boundary can be larger depending on the equipment and system parameters.
For high-fault-current equipment with slow clearing times, the arc flash boundary can extend well beyond the shock limited approach boundary. A 480V switchgear lineup with 65 kA available fault current and a 0.5-second clearing time might have an arc flash boundary of 15 to 25 feet, while the shock limited approach boundary is only 3 ft 6 in. Workers standing 10 feet away are outside the shock boundary but well inside the arc flash boundary and must wear appropriate arc flash PPE.
Conversely, for high-voltage equipment with fast clearing times and low fault currents, the shock limited approach boundary can exceed the arc flash boundary. A 13.8 kV switchgear with current-limiting fuses that clear in 0.01 seconds might have an arc flash boundary of 3 feet, while the shock limited approach boundary is 5 ft 8 in. Workers between 3 and 5.7 feet from the equipment need shock protection but may not need arc flash PPE beyond the minimum.
The practical takeaway is that both hazards must be assessed independently. The arc flash label on the equipment should include both the arc flash boundary and the shock approach boundary (or direct the worker to the appropriate table). Workers must evaluate both boundaries and comply with the requirements of whichever boundary they are inside. If they are inside both boundaries, they must meet the requirements for both shock and arc flash protection simultaneously.
Always assess shock and arc flash boundaries independently. At 480V with high fault current, the arc flash boundary is often much larger than the shock boundary. At medium voltage with fast clearing, the shock boundary may be larger. Workers must comply with the requirements for whichever boundary they are inside.
Shock Approach Boundary Calculator
Look up limited, restricted, and prohibited approach boundaries for shock protection per NFPA 70E Table 130.4(E)(a) for AC and (b) for DC. Visual boundary zone diagram included.