Working on Energized Parts

Exposed means the energized part is not isolated or guarded and is therefore accessible to contact. See the definitions in 1910.269(x) and the discussion in Appendix B to 1910.269 which explains how exposed energized parts present hazards to workers.

Guarded means that the energized part is covered, fenced, enclosed, or otherwise protected by suitable means (for example, covers, casings, barrier rails, screens, mats, or platforms) to minimize the chance of dangerous approach or inadvertent contact under normal conditions. See the definition in 1910.269(x) and the Appendix B discussion at 1910.269 App B.

Insulated means separated from other conducting surfaces by a dielectric (including air space) that offers high resistance to current flow, and it is assumed insulated only for the normal conditions it is subjected to. See the definition in 1910.269(x) and the explanatory notes in Appendix B to 1910.269.

Yes — an employer must establish minimum approach distances no less than the distances computed by Table R-3 for AC systems so employees can work safely without risk of sparkover. This requirement is set out in 1910.269(l)(3)(i) and the technical methodology employers must use is provided in Appendix B to 1910.269.

If the employer is not using the maximum transient overvoltages from Table R-9 for voltages over 72.5 kV, the employer must use persons knowledgeable in the techniques of Appendix B and competent in electric transmission and distribution system design to determine the maximum transient overvoltage. This requirement is explained in Appendix B to 1910.269 and is tied to 1910.269(l)(3)(ii).

Use a minimum air insulation distance of 20 millimeters (1 inch) as the electrical component of the minimum approach distance for voltages from 301 to 5,000 volts. Appendix B explains that test data support using 20 mm to protect against sparkover in this voltage range; see Appendix B to 1910.269 and the related requirement in 1910.269(l)(3)(i).

Follow the five-step procedure in Appendix B to compute the electrical component of the MAD for 5.1 to 72.5 kV: (1) divide the phase-to-phase voltage by √3 to get phase-to-ground RMS; (2) multiply by √2 to get peak phase-to-ground voltage; (3) multiply by the maximum per-unit transient overvoltage (3.0 for this range); (4) divide that peak transient by 0.85 to find the critical sparkover voltage; and (5) interpolate the corresponding gap distance from Table 1 in Appendix B. See Appendix B to 1910.269 and 1910.269(l)(3)(i) for the authority and details.

Interpolation is used to find the gap spacing that corresponds to the calculated critical sparkover voltage by comparing the voltage to the voltages listed in Table 1 and estimating the gap between table entries. For example, Appendix B shows a worked illustration in Table 2 where the calculated critical sparkover voltages are matched to Table 1 and linear interpolation is used to get the electrical component in centimeters, then converted where needed. See the procedure and worked example in Appendix B to 1910.269 and the requirement in 1910.269(l)(3)(i).

Use Equation 1 in Appendix B: D = 0.3048 (C + a) V_L-G T, where D is the electrical component of MAD in meters, C is a correction factor (0.01 or 0.011 depending on the gap conditions), a is the surge factor calculated from the formulas in Table 3, V_L-G is the maximum line-to-ground RMS voltage in kV, and T is the maximum transient overvoltage factor. See Appendix B to 1910.269 and 1910.269(l)(3)(ii) for the full formula and variable definitions.

Use C = 0.01 when the exposure is phase-to-ground and the employer can demonstrate the gap consists only of air, or for phase-to-phase exposures if the employer can demonstrate no insulated tool spans the gap and no large conductive object is in the gap; otherwise use C = 0.011. Appendix B explains these conditions for setting the C correction factor in Equation 1; see Appendix B to 1910.269.

Calculate 'a' using the equations provided in Table 3 of Appendix B, which vary with V_Peak ranges and whether the exposure is phase-to-ground or phase-to-phase; the table gives piecewise formulas for different V_Peak bands. See Table 3 and the explanatory text in Appendix B to 1910.269 and the reference to 1910.269(l)(3)(ii).

Paragraph (l)(3)(ii) allows employers to assume the maximum anticipated per-unit transient overvoltage in accordance with Table R-9; Appendix B also lists assumed maximums for certain voltage ranges (for example, 3.5 per unit for 72.6–420.0 kV, 3.0 per unit for 420.1–550.0 kV, and 2.5 per unit for 550.1–800.0 kV). See 1910.269(l)(3)(ii) and the related discussion in Appendix B to 1910.269.

Yes — employers may rely on normal system protection (for example, lightning arrestors) or use temporary devices or measures (such as portable protective gaps or preventing automatic breaker reclosing) to control maximum anticipated transient overvoltages that can reach the worksite. Appendix B explains that such measures can be included in the employer's approach-distance determinations; see Appendix B to 1910.269.

The minimum air insulation distance is the air gap required to prevent sparkover under the maximum transient overvoltage expected at the worksite and it is equal to the electrical component of the minimum approach distance when the employee is not using electrical protective equipment. Appendix B explains that the air must be sufficient to withstand the maximum transient overvoltage and that this air insulation distance forms the electrical component of the MAD; see Appendix B to 1910.269 and 1910.269(l)(3)(i).

Phase-to-ground exposure is when the employee is at ground potential with respect to an energized part (or the employee is at the potential of an energized part with respect to ground during barehand work); phase-to-phase exposure is when the employee is at the potential of one energized part with respect to another energized part at a different potential (for example, during barehand work spanning phases). Appendix B explicitly describes these two kinds of exposures and how they affect minimum approach distance determinations; see Appendix B to 1910.269.

No — insulated wires that are not otherwise protected are not considered "guarded." Appendix B includes a note to the definition of "guarded" that wires insulated but not otherwise protected do not meet the guarded definition; see 1910.269(x) and Appendix B to 1910.269.

Yes — the Appendix B procedures first compute the electrical component of the MAD "before the application of any altitude correction factor" and then require that an altitude correction factor be applied where appropriate; Appendix B explains altitude correction later in the appendix. See Appendix B to 1910.269 for the directive to apply altitude corrections after the base electrical calculation.

Use a maximum transient overvoltage factor of 3.0 per unit for voltages in the 5.1 to 72.5 kV range in the calculations described in Appendix B. Appendix B bases the method for this voltage range on IEEE testing and specifies the 3.0 per-unit factor used in its example procedure; see Appendix B to 1910.269 and related requirements in 1910.269(l)(3)(ii).

The appendix identifies a 20 millimeter (1 inch) minimum air insulation distance as the electrical component of the MAD for voltages from 301 up to 5,000 volts. See Appendix B to 1910.269 and 1910.269(l)(3)(i).

Convert by (1) dividing the phase-to-phase RMS voltage by √3 to get the phase-to-ground RMS voltage, then (2) multiplying that result by √2 to get the peak phase-to-ground voltage. These conversion steps are the first two steps in the 5.1–72.5 kV calculation procedure in Appendix B to 1910.269.

Because the method converts the withstand voltage to a critical sparkover voltage by dividing by 0.85 — the critical sparkover voltage is about 15% greater than the withstand voltage (representing three standard deviations), so dividing by 0.85 adjusts the peak transient to the corresponding critical sparkover value used with Table 1. See the explanation and step 4 in Appendix B to 1910.269.

Use the IEEE-derived linear formula TL-L = 1.35 TL-G + 0.45 to convert a phase-to-ground maximum transient overvoltage (TL-G) into the phase-to-phase maximum transient overvoltage (TL-L). Employers performing phase-to-phase calculations must use this value as T when applying the approach-distance equations. See the formula in Appendix B to 1910.269 and the requirement to determine maximum anticipated per-unit transient overvoltage in 1910.269(l)(3)(ii).

For voltages from 0.751 kV to 72.5 kV you must add an ergonomic component of 0.61 m (2.0 ft) to the electrical component of the minimum approach distance because, in this voltage range, the electrical component is often very small and does not protect the worker's face and unanticipated movements. Appendix B explains that gloves used at these voltages protect only hands and arms, so a larger ergonomic allowance is needed to cover slips, misjudgments, and handling errors; see Table 4 in Appendix B to 1910.269 and the discussion of the ergonomic component in 1910.269(l).

The total minimum approach distance equals the electrical component (from the appropriate MAD table) plus the ergonomic component (from Appendix B Table 4), adjusted for altitude and other correction factors where applicable. Appendix B instructs employers to add the ergonomic "adder" to the electrical component and to apply altitude and atmospheric corrections (about 3% per 1,000 ft above 3,000 ft) from the appendix when calculating MAD; see Appendix B to 1910.269 and the general requirements in 1910.269(l).

An employer may reduce the MAD by controlling transient overvoltages using the four-step process in Appendix B: (1) determine the maximum actual voltage for the energized part, (2) choose and quantify a control technique that lowers the maximum transient overvoltage (and determine the resulting withstand voltage at the 3σ confidence level), (3) require workers to follow procedures that ensure the control technique remains in effect during work, and (4) use the reduced per-unit transient overvoltage to compute the MAD from the table. See the detailed steps under "Calculation of reduced approach distance values" in Appendix B to 1910.269.

Employers must determine the maximum anticipated per-unit transient overvoltage (phase-to-ground) either by engineering analysis or by assuming values from the standard tables, and use that value (T L-G or converted T L-L) as T in the MAD equations. Appendix B explains the variability of transient causes and provides typical magnitudes in Table 5 (for example, opening surge with single restrike ≈ 3.0 per unit). See 1910.269(l)(3)(ii) and Table 5 in Appendix B for examples and guidance.

For voltages between 72.6 kV and 800 kV the ergonomic component is 0.31 m (1.0 ft). Appendix B explains this smaller ergonomic allowance reflects the use of live-line tools (hot sticks) and work methods that more tightly control worker movement, which keep the employee farther from energized parts and require greater precision; see Table 4 in Appendix B to 1910.269 and the discussion about higher-voltage work methods in 1910.269(l).

Using live-line tools typically reduces the ergonomic component because the tool design maintains a fixed distance between the worker and the energized part, so the worker's movements are more constrained; Appendix B notes these work methods are why the ergonomic component between 72.6 kV and 800 kV is 0.31 m (1 ft). Employers must still add the ergonomic distance to the electrical component when calculating MAD; see the discussion of live-line tools and Table 4 in Appendix B to 1910.269.

Employers must treat broken or damaged insulator units as having no insulating value when estimating insulator string strength for MAD purposes; the number of good units required for an insulator string to be considered "insulated" depends on the maximum overvoltage possible at the site. Appendix B also warns that a live-line tool near a damaged string can further reduce overall insulating strength. See the guidance in Appendix B to 1910.269 and the definition-related provisions in 1910.269(x).

Yes — an employer may use an engineering analysis that demonstrates a lower maximum transient overvoltage than Table R-9, but only if the employer ensures any special conditions assumed in that analysis (for example, blocking reclosing or installing protective gaps) are actually in effect during the live work; the employer may need to adopt new live-work procedures to make sure those conditions are present. See the requirement in 1910.269(l)(3)(ii) and Appendix B discussion about relying on engineering analyses in Appendix B to 1910.269.

Appendix B requires employers to correct MADs for altitude and atmospheric effects because reduced air pressure at high altitudes lowers air-gap electrical strength; specifically, increase the MAD by about 3% per 300 meters (1,000 ft) of altitude above 900 meters (3,000 ft). Appendix B explains the general effects of temperature, pressure, and humidity and points to the altitude correction factors in the appendix; see Appendix B to 1910.269 and the overall MAD rules in 1910.269(l).

Training and job planning must teach and enforce selection of proper working positions so employees can perform necessary tasks without straying into the MAD; briefings and plans must cover expected movements such as adjusting hardhats, maneuvering tools, handling passed tools and materials, and making tool adjustments. Appendix B explicitly ties these requirements to 1910.269(a)(2) (training) and 1910.269(c) (job planning/briefings); see the examples and Figure 1 in Appendix B to 1910.269.

For voltages from 0.301 kV to 0.750 kV the ergonomic component of the MAD is 0.31 m (1.0 ft). Appendix B's Table 4 lists this value and notes the employer must add it to the electrical component to obtain the full MAD; see Table 4 in Appendix B to 1910.269.

Response time-distance analysis estimates the time it takes a worker to perceive they are entering a danger zone and then stop motion toward an energized part, converting that stopping time at a reasonable motion speed into a distance to add to the electrical MAD; Appendix B explains this is the basis for the ergonomic component so it covers unanticipated movements, reaction time, and deceleration distance. See the explanation of the ergonomic component and response time-distance analysis in Appendix B to 1910.269.

Appendix B identifies several control methods such as modifying circuit breaker or switch operation to reduce switching transients, installing portable protective gaps, and blocking reclosing — employers should choose a technique when uncontrolled maximum transient overvoltages would produce unacceptably large MADs and then ensure the technique stays in effect during the work. See the section on controlling transient overvoltages and Step 2 of the MAD reduction procedure in Appendix B to 1910.269.

Employers should control maximum transient overvoltages by disabling automatic reclosing, installing surge arresters or portable protective gaps, changing system transmission practices, or applying switching restrictions. These methods are described in 1910.269AppB and the regulation 1910.269(l) requires employers to limit hazards when working on energized parts.

• Disable automatic reclosing to limit switching surges when practical.
• Use modern surge arresters or portable protective gaps to dissipate or divert transients.
• Apply switching restrictions or "hold-offs" to prevent operation until safe conditions exist.

Cited requirement: see 1910.269AppB.

Employers should disable automatic reclosing to prevent unintentional reenergization that can cause hazardous transient overvoltages or worsen injuries and equipment damage. Appendix B explains both safety and overvoltage-control reasons for disabling reclosing and warns that the employer must ensure insertion resistors and other overvoltage-limiting devices are operable if the engineering analysis depends on them. See 1910.269AppB and 1910.269(l)(3).

• If insertion resistors are part of the assumed protection, the employer must verify they will function as expected before relying on that analysis.
• If automatic reclosing cannot be disabled for system reasons, the employer must adopt other methods (e.g., arresters or gaps) to control switching surge levels.

The employer must include the effect of coupling from adjacent lines—especially with double-circuit construction—in the engineering analysis whenever employees work on a line that could see transients induced from nearby circuits. Appendix B specifically requires accounting for adjacent-line coupling because surges on an adjacent line can create significant overvoltages on the work line; see 1910.269AppB.

• Double-circuit structures and physically close parallel circuits commonly produce coupling that increases transient voltages.
• If you use default T values from the tables, you still must confirm they are conservative for your configuration; otherwise perform site-specific analysis.

The employer calculates MAD by selecting a gap withstand voltage, determining the corresponding physical gap, using 110% of the gap's critical sparkover voltage to get VPPG Peak, computing the worksite transient overvoltage factor T via T = VPPG Peak / (VL‑G√2), and then applying that T in the MAD equations or tables. Appendix B gives a five-step procedure describing this approach; see 1910.269AppB and the related rule 1910.269(l)(3)(ii).

• Step summary: pick withstand voltage → pick gap distance → VPPG Peak = 1.10×critical sparkover → compute T → use T in Table R‑3 or Tables 14–21 to obtain MAD.
• Ensure test data for the protective gap supports the selected critical sparkover voltage before relying on it.

When using the tables, employers must always round up (to the next higher value) for the minimum approach distance, and the calculated T may only be applied with Tables 14–21 if the worksite elevation is no more than 900 meters (3,000 feet) above sea level. Appendix B states these requirements; see 1910.269AppB and 1910.269(l).

• Always round MAD up to the next higher tabulated/determined value.
• If above 900 m, you must account for altitude effects or use other applicable tables/analysis.

A protective gap installed within 0.8 km (0.5 mile) of the worksite will protect against intersecting surge waves entering from opposite ends, although line-specific engineering studies may permit more distant locations. Appendix B explains the 0.8 km guidance and requires the employer to determine the worksite T unless using default table values; see 1910.269AppB.

• If you place gaps only at terminal stations, be aware terminal gaps may not protect along the entire line due to multiple surges entering from both ends.
• Document any engineering study that justifies using gaps farther than 0.8 km from the worksite.

Yes; installing the protective gap on an adjacent structure is permitted and does not significantly reduce protection for employees at the worksite. Appendix B explicitly allows adjacent-structure installation and discusses terminal-station limitations; see 1910.269AppB.

• Even when installed on adjacent structures, ensure the gap setting and location meet the engineering assumptions used to compute T and MAD.
• Remember that terminal-station gaps may not protect against surges originating mid‑line or from both ends simultaneously unless the analysis demonstrates adequate protection.

If disabling automatic reclosing is not possible, the employer must use alternative overvoltage-control methods such as surge arresters, protective gaps, changing the transmission system to reduce switching effects, or establishing switching restrictions and hold-offs, and must reflect those measures in the engineering analysis. Appendix B notes that when reclosing cannot be disabled, other methods of controlling switching surge level are necessary; see 1910.269AppB and 1910.269(l)(3).

• Document and validate any alternative controls and verify equipment (arresters, gaps, resistors) will function as assumed.
• Use switching restrictions (tags/hold-offs) to modify breaker operation during the live work when appropriate.

A "hold-off" or "restriction" is a tagging system that limits or modifies the operation of switching devices (it does not entirely prevent operation) during live-line work; employers should implement it similarly to a permit/tagging system to ensure switching does not create hazards. Appendix B describes hold-off practices and their role in switching restrictions; see 1910.269AppB and 1910.269(l).

• A hold-off should clearly identify the work activity, responsible personnel, and required conditions before any switching.
• Employers must ensure the hold-off procedure aligns with any system constraints and the engineering analysis assumptions.

Employers must protect employees from hazards resulting from any sparkover of the protective gap, because lightning strikes several miles away or other overvoltages can cause gap sparkover; Appendix B warns that sparkover can occur from strikes up to 6 miles away and requires employers to protect workers from those events. See 1910.269AppB.

• When working beneath a gap, address the direct hazard from a sparkover (arc, flash, overvoltage) through safe work procedures and PPE.
• Ensure the engineering analysis considers the possibility and consequences of gap sparkover and documents protective measures.

Employers should use verified test data for a specific protective gap to select the spacing that yields a critical sparkover voltage equal to or greater than the required withstand voltage—Appendix B demonstrates selecting a gap whose tested critical sparkover meets the calculated need. See 1910.269AppB.

• Example procedure: compute required withstand voltage → divide by appropriate factor (e.g., 0.85 in the sample) → choose gap with test-proven critical sparkover ≥ that voltage.
• Keep and retain test records and use the tested crest (critical) sparkover value when computing VPPG Peak (VPPG Peak = 1.10 × critical sparkover per Appendix B).

Employers can use the MAD tables in Appendix B (Tables 6–13 and Tables 14–21) to obtain minimum approach distances for specified overvoltage factors T; Appendix B also notes that Tables 6–13 could be used until March 31, 2015, implying that employers should refer to the current tables and the standard 1910.269(l)(3)(ii) for the applicable table set. See 1910.269AppB.

• Use the tables that correspond to the regulatory version and date applicable to your work (confirm current regulatory effective dates).
• If you determine T by engineering analysis, you may apply the distances from the tables that incorporate T, subject to the altitude and rounding rules in Appendix B.

You may use the distances in Table 11, Table 12, or Table 13 only when you have determined the maximum anticipated per‑unit transient overvoltage (T) by engineering analysis, as required by 1910.269(l)(3)(ii).

• Do the engineering analysis called out in 1910.269(l)(3)(ii) to estimate the maximum anticipated per‑unit transient overvoltage (T).
• Once you determine T, select the matching row in the appropriate table (Table 11 for 242.1–362.0 kV, Table 12 for 362.1–552.0 kV, or Table 13 for 552.1–800.0 kV) in 1910.269 Appendix B to get the MAD.
• Ensure the table notes apply (for example, Note 1 in those tables permits their use only when the engineering analysis establishes the T value).

Also verify other Appendix B requirements that affect applicability (for example, elevation limits and phase‑to‑phase conditions); see 1910.269 Appendix B for the full set of table notes and conditions.

T (p.u.) is the maximum anticipated per‑unit transient overvoltage (peak system voltage expressed as a multiple of nominal operating voltage) that you use to pick a minimum approach distance in the Appendix B tables. You must determine T by engineering analysis or, where allowed, use an assumed value in accordance with 1910.269(l)(3)(ii) and the procedures in 1910.269 Appendix B.

• Use the equations and guidance referenced in Appendix B (for example, Table R‑3 and the explanatory notes) to calculate T from peak voltage or system characteristics.
• Apply practical design considerations in Appendix B (such as the recommendation that employers often add a 0.2 margin to T per Appendix B Note 12) when you judge it appropriate for system reliability and safety.
• Document the engineering analysis and assumptions (peak voltages, surge‑limiting devices, protective gaps, arrester effects, and any conservative margins) so you can justify the chosen T and the MAD selected from the tables.

See 1910.269 Appendix B for the equations, notes, and practical guidance used to derive and apply T when determining MADs.

For phase‑to‑phase exposures, you must demonstrate that no insulated tool spans the gap and that no large conductive object is in the gap before you may rely on the table distances for phase‑to‑phase MADs, as stated in 1910.269 Appendix B Note 2.

• Practical demonstrations include documented site inspection, work procedures that keep tools and equipment out of the gap, physical barriers, or engineering controls that prevent conductive objects from bridging the phase‑to‑phase space.
• Also confirm the other table prerequisites (for example, the worksite elevation limit and any engineering analysis for T) found in 1910.269 Appendix B.

Keep written evidence (inspection records, procedures, photos, or engineering notes) showing how you ensured no insulated tool spans the gap and no large conductive object is present, so you can demonstrate compliance with Appendix B conditions.