Electric potential hazard protection

A voltage-gradient distribution is the way voltage falls off with distance from a grounding electrode during a ground fault, and it matters because it creates different voltages at nearby points that can put workers at risk of electric shock. Appendix C explains that the earth around a grounded object develops a ground potential gradient and that voltages decrease rapidly with distance from the grounding point, so workers standing or touching objects at different distances from the electrode can experience hazardous step or touch potentials (Appendix C to Subpart V of Part 1926).

• Practical effect: the voltage at a crane frame, tower, or nearby ground is not uniform; differences in potential between a worker’s feet and a touched object can cause current to flow through the body.
• Compliance reference: see Appendix C to Subpart V of Part 1926 for the voltage-gradient discussion and Figure 1 illustrating the distribution.

Step potential is the voltage difference between a person’s feet when standing near an energized grounded object, and touch potential is the voltage difference between the object and the person’s feet when the person touches the object; both can cause current through the body and injury. Appendix C defines step potential as the voltage difference between two ground points at different distances from the electrode (each foot) and touch potential as the voltage difference between the electrode and the worker’s feet, and it shows how these can be nearly the full fault voltage in some cases (Appendix C to Subpart V of Part 1926).

• Example: a worker touching a crane grounded at the neutral could see a touch potential nearly equal to the full impressed fault voltage.
• Compliance reference: see the definitions and Figure 2 in Appendix C to Subpart V of Part 1926.

Employers can protect ground-level workers by using equipotential zones, properly rated insulating equipment, or by restricting access to hazardous areas. Appendix C III.C explains those three methods and notes that the employer should choose measures based on an engineering analysis of the fault conditions (Appendix C to Subpart V of Part 1926).

• Equipotential zones: create an area (for example, with a metal mat or grounding grid) tied to the grounded object so the worker and object are at the same potential.
• Insulating equipment: use rubber gloves or other rated insulating gear sized to the highest impressed voltage expected under fault conditions (not simply the system voltage).
• Restricted work areas: keep nonessential employees at distances where step voltages cannot cause injury.

See Appendix C to Subpart V of Part 1926 for guidance and consider the related protective grounding requirements in 1926.962.

Insulating equipment must be rated for the highest voltage that can be impressed on the grounded objects under fault conditions, not automatically for full system voltage. Appendix C III.C.2 explains that the required rating depends on the voltage remaining on conductive objects after bonding and grounding are installed, so employers must use an analysis of potential impressed voltages to select proper insulating equipment (Appendix C to Subpart V of Part 1926).

• Practical step: perform an engineering analysis or use the Appendix C guidelines to determine the maximum impressed voltage expected during a fault, then choose insulating PPE with a voltage rating at or above that value.
• Compliance reference: see Appendix C to Subpart V of Part 1926 and protective grounding requirements in 1926.962.

The employer must demonstrate that temporary protective grounds are placed and arranged so they will prevent exposure of each employee to hazardous differences in electric potential. Paragraph (c) of 1926.962 requires this demonstration, and Appendix C III.D provides guidelines employers can use to meet that requirement and notes that following the appendix criteria will be considered compliance with 1926.962(c) (Appendix C to Subpart V of Part 1926).

• Employers can make the demonstration either through an engineering analysis (III.D.1) or by using the grounding methods described in III.D.2.
• Compliance references: 1926.962(c) and Appendix C to Subpart V of Part 1926.

An employer should use the equation from IEEE Std 1048-2003, I = 116/√t, to estimate the ventricular fibrillation threshold for current as a function of shock duration, and then account for body resistance to convert that current limit into a safe voltage limit in the work area. Appendix C III.D.1 specifically cites the IEEE equation and explains how to use it for current durations between 0.0083 and 3.0 seconds (Appendix C to Subpart V of Part 1926).

• Steps: determine the likely fault-current duration (t), compute safe current I = 116/√t, choose a body resistance assumption (see next QA), and calculate the corresponding safe voltage (V = I × R).
• Compliance reference: Appendix C to Subpart V of Part 1926 (see III.D.1) and consider 1926.962(c) for protective grounding obligations.

Employers may use 1000 ohms as a common assumed total body resistance for calculating body current limits, but they should also be aware that body impedance can be much lower (examples: hand-to-hand 610 Ω, internal body ~500 Ω), so they should use conservative (lower) resistance values when appropriate. Appendix C cites IEEE Std 1048-2003 and notes the 1000 Ω assumption and the reported lower resistances that better represent worst-case (wet skin, cuts) conditions (Appendix C to Subpart V of Part 1926).

• Practical guidance: use a lower resistance assumption (e.g., 500 Ω) when workers could be wet, injured, or otherwise have reduced skin resistance to ensure safety.
• Compliance reference: Appendix C to Subpart V of Part 1926 (III.D.1 discussion of IEEE Std 1048-2003).

A 1 mA threshold is used to identify a hazard when precautions taken do not adequately protect employees from involuntary reactions to shock; Appendix C says a hazard exists if the induced voltage could pass 1 mA through a 500-ohm resistor (threshold of perception). This threshold is used as a conservative trigger for hazard recognition when involuntary reaction risks have not been otherwise controlled (Appendix C to Subpart V of Part 1926).

• Calculation basis: 1 mA × 500 Ω = 0.5 V; if potential differences could produce that current under likely conditions, additional controls are required.
• Compliance reference: Appendix C to Subpart V of Part 1926 (III.D.1 text discussing perception threshold).

The 6 mA threshold applies when the duration of the electric shock is unlimited (i.e., when fault current will not be interrupted by protective devices); Appendix C states a hazard exists if the resultant current would be more than 6 mA, which is the recognized let-go threshold for workers. Employers must prevent sustained currents above this level by design or controls when circuit interruption is not assured (Appendix C to Subpart V of Part 1926).

• Meaning: currents above the let-go threshold may cause a worker to be unable to release a conductor or otherwise suffer dangerous muscular contractions.
• Compliance reference: Appendix C to Subpart V of Part 1926 (III.D.1 discussion of perception and let-go thresholds).

Yes — Appendix C III.D.2 describes grounding methods that employers can use in lieu of an engineering analysis, and OSHA will consider employers that comply with those criteria to meet 1926.962(c). Appendix C states these methods are designed to keep differences in electric potential as low as reasonably possible and thus satisfy the demonstration requirement without a formal engineering study (Appendix C to Subpart V of Part 1926).

• Practical step: follow the specific grounding configurations and placement criteria in III.D.2 of Appendix C whenever you opt not to perform a detailed engineering analysis.
• Compliance references: Appendix C to Subpart V of Part 1926 and 1926.962(c).

An equipotential zone is an area in which the worker and nearby conductive objects are held at essentially the same electrical potential, and you establish it by using a metal mat, grounding grid, or bonding conductive objects together and tying them to the grounded object so that step and touch potentials within the zone are minimized. Appendix C III.C explains the equipotential-zone concept and says employers can create one by connecting a metal mat or grounding grid to the grounded object to equalize voltage within the protected area (Appendix C to Subpart V of Part 1926).

• Note: Equipotential zones protect only workers fully inside the zone; workers partially outside are not protected.
• Compliance reference: Appendix C to Subpart V of Part 1926 (III.C.1 and surrounding discussion).

Bonding or grounding an object outside the immediate work area can change the voltage distribution and raise the potential difference between that object and the worker, increasing touch potential; Appendix C warns that bonding an object outside the work area can increase the touch potential to that object and thus create a hazard. Employers must consider how external bonds alter the voltage-gradient before bonding distant objects (Appendix C to Subpart V of Part 1926).

• Practical caution: only bond or ground surrounding objects after analyzing how that action affects potentials; use an engineering analysis or follow Appendix C guidance to avoid creating new hazards.
• Compliance reference: Appendix C to Subpart V of Part 1926 (III.C.1 discussion).

Employers must select insulating equipment rated for the highest voltage that can be impressed on grounded objects under fault conditions after bonding and grounding are in place, and Appendix C recommends using an engineering analysis of the system under fault conditions to determine that impressed voltage. Appendix C III.B and III.C.2 specifically state the employer should analyze the remaining voltages after grounding and then select insulating equipment with an appropriate rating (Appendix C to Subpart V of Part 1926; see also 1926.962).

• Action: perform or obtain the analysis showing expected impressed voltage, then choose PPE (rubber gloves, sleeves, etc.) with certifications and voltage ratings equal to or above that maximum.
• Compliance references: Appendix C to Subpart V of Part 1926 and 1926.962.

Employees must not handle grounded conductors or equipment likely to become energized to hazardous voltages unless they are working inside an equipotential zone or are protected by properly rated insulating equipment. Appendix C explicitly states this prohibition and shows protection methods including equipotential zones and insulating PPE (Appendix C to Subpart V of Part 1926).

• Protections: either be inside an equipotential zone established around the grounded object or wear insulating equipment rated for the maximum expected impressed voltage.
• Compliance references: Appendix C to Subpart V of Part 1926 and the grounding requirements in 1926.962.

A grounding cable (grounding jumper) is a cable that connects a deenergized part to ground and carries fault current, whereas a bonding cable connects two conductive parts to maintain a common potential and generally does not carry substantial fault current; the difference matters for sizing and placement because grounding cables must be able to carry fault currents safely while bonding jumpers focus on equalizing potential (Appendix C to Subpart V of Part 1926).

• Practical implication: use appropriately sized conductors and connectors for grounding jumpers because they must safely carry fault currents; bonding jumpers are selected for conductivity and reliability to maintain equipotential.
• Compliance reference: definitions in Appendix C to Subpart V of Part 1926.

A ground mat (grounding grid) is a temporary or permanent metallic mat or grating that creates an equipotential surface and provides attachment points for grounds; it protects workers by equalizing the voltage across the work area so step and touch potentials are minimized. Appendix C defines a ground mat and describes its use for establishing an equipotential zone (Appendix C to Subpart V of Part 1926).

• Use case: place the ground mat where workers will stand and bond it to the grounded object so the worker and object are at nearly the same potential.
• Compliance reference: Appendix C to Subpart V of Part 1926 (definition and discussion of equipotential zones).

A cluster bar is a temporary terminal attached to a structure that provides attachment points for grounding and bonding cables, and you use it to simplify and organize temporary grounding and bonding at a work site. Appendix C defines a cluster bar as a convenient connection point that helps establish proper grounding/bonding for protective grounding systems (Appendix C to Subpart V of Part 1926).

• Practical use: install a cluster bar on a structure (like a pole or tower) to connect multiple grounding and bonding jumpers in a reliable, inspectable way.
• Compliance reference: Appendix C to Subpart V of Part 1926 (definition of cluster bar).

Duration is critical because the ventricular fibrillation threshold depends on how long current flows through the body; the IEEE equation cited in Appendix C (I = 116/√t) shows that allowable current decreases as shock duration increases, so employers must consider both current magnitude and duration when setting protections (Appendix C to Subpart V of Part 1926).

• Practical point: shorter-duration faults allow higher transient currents without the same fibrillation risk, while long-duration currents require lower limits.
• Compliance reference: Appendix C to Subpart V of Part 1926 (III.D.1 citing IEEE Std 1048-2003 and the I = 116/√t relation).

Employers should restrict nonessential employees from areas where step or touch potentials could arise by ensuring they remain at distances where step voltages are insufficient to cause injury, as recommended in Appendix C.III.C.3 and related text, or by using barriers and signage to enforce exclusion zones (Appendix C to Subpart V of Part 1926).

• Practical measures: mark and enforce exclusion zones, provide elevated platforms or remote observation points, and train employees about hazardous distances.
• Compliance references: Appendix C to Subpart V of Part 1926 and the protective grounding requirements in 1926.962.

Yes — employers must assess workplace hazards and provide written certification of the hazard assessment if PPE will be required; OSHA's PPE LOI clarifies that employers must evaluate hazards before selecting PPE, and Appendix C also directs employers to use engineering analysis to determine required insulating equipment ratings. See the PPE hazard-assessment interpretation and Appendix C for how to apply that assessment to insulating equipment selection (OSHA LOI: https://www.osha.gov/laws-regs/standardinterpretations/2024-03-28 and Appendix C to Subpart V of Part 1926).

• Required action: perform a hazard assessment, document it in writing if PPE will be required, and select insulating equipment based on the assessed impressed voltages and listed PPE ratings.
• References: OSHA PPE LOI (2024-03-28) at https://www.osha.gov/laws-regs/standardinterpretations/2024-03-28 and Appendix C to Subpart V of Part 1926 (III.B and III.C.2 guidance).

If a deenergized, grounded power line is grounded at a point remote from where a worker contacts it and it becomes energized, the touch potential at the contact point can be nearly the full fault voltage on the grounded object. Appendix C explains that touch potential may equal the voltage difference between the electrode (distance 0) and the worker's feet, and grounding only at a remote point can leave substantial voltage across the object under fault conditions (Appendix C to Subpart V of Part 1926).

• Practical implication: avoid grounding only at a remote point if workers will touch the line; instead use methods (equipotential zones, local bonding/grounds) from Appendix C to minimize touch voltages.
• Compliance reference: Appendix C to Subpart V of Part 1926 (touch-potential discussion and examples).

Soil resistivity and texture affect how rapidly voltage dissipates from the grounding electrode; Appendix C notes that Figure 1 assumes uniform soil texture and that in reality soil conditions change the shape and extent of the voltage-gradient distribution, which can increase or decrease the area affected by hazardous step and touch potentials (Appendix C to Subpart V of Part 1926).

• Practical consequence: in rocky or high-resistivity soils the gradient may extend further and increase hazardous areas, so employers should include soil conditions in any engineering analysis or when establishing equipotential zones.
• Compliance reference: Appendix C to Subpart V of Part 1926 (voltage-gradient distribution discussion).

An engineering analysis is recommended when assessing the power system under fault conditions to determine whether hazardous step and touch voltages will develop; Appendix C III.B says the analysis should determine voltages on conductive objects and the duration the voltage will be present so the employer can select appropriate protective measures and PPE (Appendix C to Subpart V of Part 1926).

• Analysis outcomes: expected impressed voltages on all conductive objects, duration of voltage under fault, and residual voltages after bonding/grounding so PPE and grounding schemes can be sized correctly.
• Compliance references: Appendix C to Subpart V of Part 1926 and 1926.962 for protective grounding requirements.

OSHA will accept either an engineering analysis demonstrating that temporary protective grounds, placed and arranged as used, will prevent hazardous potential differences or compliance with the grounding methods and criteria specified in Appendix C III.D.2, which OSHA considers sufficient to meet [1926.962(c)]. The employer must be able to show that the chosen grounding arrangement protects each employee from hazardous step and touch potentials (1926.962(c) and Appendix C to Subpart V of Part 1926).

• Documentation options: engineering calculations, wiring/grounding diagrams, testing records, or a clear description of applied Appendix C grounding methods and inspection/maintenance records.
• Compliance references: 1926.962(c) and Appendix C to Subpart V of Part 1926 (III.D guidance).

A crane grounded to the system neutral that contacts an energized line can expose anyone touching the crane or its uninsulated load line to a touch potential nearly equal to the full fault voltage, making it especially hazardous. Appendix C gives that example to illustrate that grounded mechanical equipment can carry significant impressed voltages under fault conditions (Appendix C to Subpart V of Part 1926).

• Practical precautions: use insulating links, maintain minimum approach distances, establish equipotential zones, and follow protective grounding/bonding procedures described in Appendix C and 1926.962.
• Compliance reference: Appendix C to Subpart V of Part 1926 (example regarding cranes).

Employers should base insulating-equipment selection on the highest impressed voltage that can occur on grounded objects during fault conditions after grounding/bonding are installed, determined by engineering analysis or Appendix C-compliant grounding methods; Appendix C III.B and III.C.2 stress choosing insulating PPE rated for that highest expected impressed voltage rather than automatically using the full system voltage rating (Appendix C to Subpart V of Part 1926).

• Action steps: perform or obtain the analysis showing maximum impressed voltage, then select insulating gloves, mats, and tools rated to at least that voltage.
• Compliance references: Appendix C to Subpart V of Part 1926 and protective grounding requirements in 1926.962.

Grounding connects equipment or a deenergized part to earth so fault current has a path to ground and can be cleared, while bonding connects conductive parts to each other to keep them at the same potential; grounding carries fault current and requires conductors sized for fault duty, but bonding's job is to equalize voltage so step/touch potentials are minimized. Appendix C defines both terms and notes that grounding cables carry fault current whereas bonding cables generally do not (Appendix C to Subpart V of Part 1926).

• Practical outcome: use grounding jumpers to safely carry and clear a fault; use bonding jumpers to create an equipotential zone and reduce voltage differences between nearby conductive objects.
• Compliance reference: definitions in Appendix C to Subpart V of Part 1926.

A grounding cable carries fault current whenever it connects a deenergized part to ground and a ground fault occurs; Appendix C notes grounding cables carry fault current (and must be sized accordingly), whereas bonding cables generally do not carry substantial fault current. Therefore, grounding conductors must be selected and installed to safely carry the maximum expected fault current without damage (Appendix C to Subpart V of Part 1926).

• Practical requirement: select grounding jumpers rated for fault currents and with secure, low-resistance connections, inspect them before use, and follow the grounding methods in Appendix C.
• Compliance reference: Appendix C to Subpart V of Part 1926 (definitions and grounding discussion).

Employers should follow the additional safety considerations in Appendix C III.D.3 and the requirements of 1926.962, which include proper placement, inspection, testing, and maintenance of protective grounds, training for employees, and ensuring grounds are arranged to prevent hazardous potential differences. Appendix C states that III.D.3 discusses other safety considerations that support compliance with 1926.962 and that following these guidelines helps protect workers if a deenergized and grounded line becomes energized (Appendix C to Subpart V of Part 1926; see 1926.962).

• Practical items to include: pre-use inspection and testing of grounding clamps and jumpers, documented procedures for applying/removing grounds, training on equipotential-zone establishment, and periodic audits.
• Compliance references: Appendix C to Subpart V of Part 1926 (III.D.3) and 1926.962.

Appendix C does not list a single numeric separation distance; instead, it requires employers to ensure employees on the ground are at a distance where step voltages would be insufficient to cause injury, based on an engineering analysis or the use of Appendix C grounding and equipotential methods. Employers must evaluate the voltage gradient for the specific site and ensure exclusion distances or protective measures are used accordingly (Appendix C to Subpart V of Part 1926).

• Practical approach: perform a site-specific analysis considering soil, system voltage, and grounding arrangement or establish equipotential zones and barriers to keep workers at safe distances.
• Compliance reference: Appendix C to Subpart V of Part 1926 (III.C.3 guidance on restricting employees).

The grounding method must (1) make the circuit open in the fastest available clearing time and (2) keep potential differences between conductive objects in the worker's area as low as possible. These are the two guiding principles set out in Appendix C to Subpart V, 29 CFR 1926 and referenced by 1926.962.

• Maximizing fault current with a low-impedance connection speeds clearing by protective devices.
• Bonding conductive objects in the work area reduces voltage differences that could expose a worker to hazardous touch or step potentials.

An employer must perform an engineering analysis when their grounding practices do not follow the two principles (fastest clearing time and minimizing potential differences) and they need to demonstrate that their protective grounds "will prevent exposure of each employee to hazardous differences in electric potential." This requirement is in 1926.962(c) and explained in Appendix C to Subpart V, 29 CFR 1926.

• The analysis should show how the chosen grounding locations and arrangements protect each employee from hazardous potential differences.
• If you deviate from grounding to the best available low-impedance point (like a system neutral or substation grid), document the technical basis that exposures remain safe.

An employer should ground the circuit conductors to the best ground available on the worksite—preferably a grounded system neutral or a substation grounding grid—because these provide the lowest impedance and maximize fault current for faster clearing. This guidance is in Appendix C to Subpart V, 29 CFR 1926 and supports the objectives of 1926.962.

• Remote pole or tower grounds may be used only when a grounded neutral or substation grid is not available.
• If none of those exist, a temporary driven ground at the worksite is acceptable as a last resort.

If a conductor is not grounded at the worksite, the employer must treat that conductor as energized because an ungrounded conductor can be energized at fault voltage during a fault. This is explained in Appendix C to Subpart V, 29 CFR 1926 and relates to the requirements of 1926.962.

• For three-phase systems, the grounding method must short-circuit all three phases to ensure faster clearing and to reduce voltage across the grounding cable.
• The short circuit that bonds phases need not be at the immediate worksite, but any conductor left ungrounded locally must be treated as energized.

The employer must bond all conductive objects in the work area so they are at essentially the same potential, using bonding cables or reliable metal-to-metal contact that is tight and free of corrosion. This requirement is in Appendix C to Subpart V, 29 CFR 1926 and supports 1926.962.

• Use bonding cables for electrical continuity unless the metal-to-metal contact is mechanically tight and uncontaminated.
• Inspect bolted or welded connections for tightness and corrosion to maintain low impedance across the bond.

Employers must either provide a conductive platform bonded to the grounding cable for the worker to stand on or install cluster bars that bond the wood pole to the grounding cable, placing the cluster bar below and close to the worker's feet. This requirement and the details are in Appendix C to Subpart V, 29 CFR 1926 and relate to 1926.962.

• Because wood poles can conduct when wet, the cluster bar must make conductive contact with a metal spike or nail that penetrates at least as deep as the worker's climbing gaffs will.
• Alternatives include mounting the cluster bar on a bare pole ground wire or temporarily nailing a conductive strap and bonding it to the cluster bar.

If a cable is cut, the employer must install a bond across the opening in the cable or install a bond on each side of the opening so the separate cable ends are at the same potential, and workers must stand on a conductive mat bonded to the deenergized cable to form an equipotential zone. This guidance appears in Appendix C to Subpart V, 29 CFR 1926 and supports the protections required by 1926.962.

• Before the mat is bonded to the cable, the employer must protect the worker from hazardous potential differences (for example, by keeping workers away until bonds are installed).

Employers must maintain grounding cables, clamps, and bonding connections so they are clean, tight, free of corrosion or damage, and capable of carrying fault current without failure. This maintenance guidance is in Appendix C to Subpart V, 29 CFR 1926 and supports the protective grounding requirements in 1926.962.

• Inspect clamps and bonding surfaces for corrosion or oxidation and clean them when needed.
• Replace damaged or worn grounding cables and ensure clamps are tightly secured to conductors or tower members.

Grounding cables should be as short as practicable because longer cables increase electromagnetic forces and movement during a fault, which can damage cables, separate clamps, or cause flying cables that injure workers. This safety guidance is in Appendix C to Subpart V, 29 CFR 1926 and supports the objectives of 1926.962.

• Route high-current grounding cables so they cannot strike or injure workers if they move during a fault.
• Keep attachment points close to the worksite unless otherwise required for safe equipotential or clearing performance.

Yes—an employer may use a remote pole or tower ground when a grounded system neutral or substation grounding grid is not available, but remote grounds have higher impedance which can reduce fault current and slow clearing times compared to a system neutral or substation grid. This allowance and trade-off are described in Appendix C to Subpart V, 29 CFR 1926 and relate to the requirements of 1926.962.

• If using remote grounds, the employer should evaluate whether the higher impedance might create hazardous potential differences and consider performing an engineering analysis per 1926.962(c).

Yes—metal lattice tower members can be considered bonded conductive objects when connections (for example, bolted connections) are tight and free of corrosion or contamination that would increase impedance. This practice is described in Appendix C to Subpart V, 29 CFR 1926 and supports compliance with 1926.962.

• Regularly inspect and clean bolted or welded connections to maintain low-resistance metal-to-metal contact.
• Use bonding cables where metal-to-metal contact is not reliable or could become contaminated.

Employers must bond the conductive mat to the deenergized cable at the worksite so both the mat and cable are at the same potential before workers stand on it; until that bond exists, the worker must be protected from hazardous potential differences. This requirement and rationale are in Appendix C to Subpart V, 29 CFR 1926 and implement the protections of 1926.962.

• If the cable is interrupted, install a bond across the cut or bonds on both sides so separated ends share the same potential.

Corrosion and contamination on clamps or connection surfaces increase resistance, which can raise potential differences and reduce the grounding system's effectiveness, so employers must keep clamp surfaces and attachment points clean and free of corrosion. This maintenance guidance is in Appendix C to Subpart V, 29 CFR 1926 and helps meet the protective-grounding expectations of 1926.962.

• Inspect clamps and bonding surfaces before use and clean, recondition, or replace components with corrosion or high-resistance coatings.
• Ensure clamps remain tight during work so they do not separate under fault conditions.

Bonding conductive objects reduces voltage differences across a worker's body so that less current flows through the worker during a fault, lowering the chance of reaching the recognized "let-go" threshold of about 6 mA that can cause loss of muscle control. Appendix C explains the need to minimize potential differences for safety in Appendix C to Subpart V, 29 CFR 1926 and this supports the objectives of 1926.962.

• Equipotential zones and proper bonding aim to keep touch and step voltages low so currents through the body stay below hazardous levels.