Substation Touch and Step Voltage

A safe substation earthing system is not the one with the lowest resistance; it is the one that controls touch, step and transferred potentials for credible fault current, clearing time, soil and operating conditions while maintaining reliable equipotential bonding. A single ground-resistance number cannot demonstrate that result.

This guide connects IEC installation requirements, the IEEE 80 design methodology, current IEEE measurement practice and practical MV switchgear interfaces. It also explains the 2026 standards position: IEEE 80-2013 is now listed as Inactive-Reserved while a replacement P80 project is active; IEEE 81-2025 is the active measurement guide and supersedes IEEE 81-2012.

Executive conclusions

Design against shock exposure, not a universal “1 ohm” target.
Ground potential rise (GPR) depends on grid current and grid impedance; not all calculated earth-fault current enters the local grid.
Touch and step voltage are spatial, time-dependent exposure quantities—not the same as GPR.
Determine maximum credible grid current, X/R, fault duration including backup, and current split through neutrals, shield wires, cable screens and remote grids.
Model layered soil from measured resistivity; dry, frozen or seasonal surface layers can govern risk.
Permissible limits depend on fault duration, body-current criterion, surface-layer resistance and governing rules. Do not copy a generic touch-voltage value.
Bond switchgear, structures, doors, fences, gates, cable sheaths, rails and services deliberately; transferred potential can move risk beyond the fence.
Verify thermal and mechanical fault duty, corrosion compatibility and permanent-connection qualification—not only electrical resistance.
Commission with a planned set of resistivity, integrity, impedance and surface-potential tests; no single test proves the whole design.
Update the model after fault level, topology, conductor, building, fence, cable or soil changes.

1. Current standards map

Reference	Status at August 2026	Engineering use
IEC 61936-1:2021	Current IEC installation standard	Earthing-system, safety and installation requirements above 1 kV AC
IEEE 80-2013	Inactive-Reserved since 2024; replacement P80 project active	Established quantitative AC substation grounding methodology, where contract/regulator accepts it
IEEE P80	Active project, not a published standard	Monitor; do not cite a draft as a completed standard
IEEE 81-2025	Active; published 15 July 2026; supersedes 81-2012	Earth resistivity, ground impedance, touch/step surface potentials and integrity measurements
IEEE 837-2024	Active; published 2025	Qualification of permanent substation grounding connections

Project documents must state the governing edition and jurisdiction. The inactive status of IEEE 80-2013 does not erase its technical method, but it does require an explicit contractual decision, recorded deviations and monitoring of the P80 revision. Do not market P80 as published.

2. Essential quantities

Earth-fault current: total fault current supplied by all sources at the fault location.
Grid current, Ig: portion flowing from the local grounding system into surrounding earth after current splits are considered.
Grid impedance, Zg: power-frequency impedance between the grid and remote earth, including resistive/reactive effects as applicable.
Ground potential rise: approximately GPR = Ig × Zg for the defined condition; use the full model where phase and mutual effects matter.
Touch voltage: potential difference bridged by a person touching a grounded object while standing on the surface.
Step voltage: surface-potential difference between two points separated by the defined step distance.
Mesh voltage: worst touch-type exposure within a grid mesh under the selected model.
Transferred potential: grid potential carried into/out of the site by a metallic conductor or bonded system.

GPR can be high while accessible touch voltage is controlled by equipotential design; a low measured ground resistance can coexist with a dangerous local gradient. Report the exposure map, not only R = V/I.

3. Define the shock-exposure scenarios

single-line-to-earth faults in switchgear, transformers, cables and overhead terminals;
faults on the line side versus bus side of protection zones;
maximum and minimum network topology, ties and generation dispatch;
primary clearing and credible backup/breaker-failure duration;
person inside yard, at gates/fences, in control building and outside the site;
hand-to-feet contact with structures, doors, mechanisms and cable screens;
step exposure near electrodes, grid edges, downleads and temporary earths;
transferred voltage through LV neutral, telecom, water, gas, rail, pipe or remote cable sheath;
construction/maintenance states before the permanent grid is complete;
simultaneous lightning or high-frequency phenomena assessed separately where relevant.

4. Fault current and clearing time

Start from a validated short-circuit and protection study. For each scenario record symmetrical current, DC offset/X/R as required for conductor duty, source contributions, zero-sequence path and clearing time. The earthing safety duration is the time the hazardous potential persists, including relay, logic, trip circuit and breaker interruption. Also test the credible backup path: a lower current with slower backup clearing may govern permissible exposure or conductor heating.

include utility, transformer, generator, motor and converter contribution;
model resistance/reactance of neutrals, grounding transformers and NGRs;
include multiple voltage levels coupled through transformer connections;
verify protection sensitivity at minimum earth-fault current;
use future fault level and planned network expansion where specified;
separate personnel-safety duration from thermal short-time rating if their scenarios differ.

5. Current split: why total fault current is not grid current

Part of the fault current returns through overhead shield wires, cable metallic screens/sheaths, neutral conductors, counterpoise, pipelines and interconnected remote grids. A current-split factor converts total fault current to the portion injected into local soil. The split changes with conductor bonding, line/cable mix, tower footing impedance, remote-grid impedance and frequency.

build an explicit return-path diagram;
use conductor impedances and mutual coupling appropriate to the route;
model single-point versus both-end cable-screen bonding;
consider parallel circuits and future cable additions;
perform sensitivity where remote impedances are uncertain;
measure or validate current distribution during commissioning where practical;
avoid both unconservative omission and blindly conservative 100% injection without documenting impact.

6. Soil resistivity is a model, not one number

Use field measurements over spacings that interrogate the relevant depths and across the planned footprint. Fit a uniform or multi-layer soil model with documented residuals and engineering judgment. A short-spacing measurement alone characterizes near-surface soil, not deep-current dispersion.

survey multiple directions to expose geological variation and buried metallic interference;
record moisture, temperature, season, recent weather and electrode geometry;
remove or explain distorted points rather than silently averaging them;
test dry/frozen/high-resistivity seasonal cases;
coordinate boreholes and rods with utilities, foundations and environmental constraints;
retain raw readings, instrument calibration and inversion assumptions;
use IEEE 81-2025 measurement guidance and state any alternative national method.

7. Permissible touch and step voltage

No single touch-voltage value is valid for every substation. The allowable exposure depends on the selected body-current criterion, body mass/model specified by the governing method, fault duration, contact path and resistance of footwear/surface layer. The design report must show the governing equations/curves and assumptions from the adopted standard—not a value copied from another project.

High-resistivity crushed rock can increase the foot-contact resistance and improve tolerable limits, but only if its resistivity, thickness, coverage and long-term condition are verified. Contamination, fine material, standing water, vegetation, vehicle traffic and mixing with soil can reduce performance. Never use surface material as the sole control without lifecycle inspection.

8. Grid geometry and mitigation levers

Measure	Main effect	Important limitation
Denser mesh near equipment	Reduces local touch/mesh gradients	Must coordinate with foundations and fault-current duty
Perimeter conductor/gradient control	Controls edge, fence and gate gradients	Can shift hazard outside the boundary if poorly designed
Deep rods/electrodes	Access lower-resistivity layers and reduce impedance	May have limited effect in layered soil; corrosion/utility risk
High-resistivity surface layer	Raises foot-contact resistance	Condition and wet-season performance must be maintained
Fast fault clearing	Reduces shock duration and thermal duty	Protection security, selectivity and breaker failure remain
Isolation of transferred services	Interrupts hazardous metallic path	Must preserve EMC, lightning and functional requirements
Equipotential mats	Controls local operator touch exposure	Bonding and perimeter gradient need analysis

9. MV switchgear bonding details

bond the switchgear earth bar to the station grid at engineered points and conductor sizes;
verify continuity across shipping splits, bus sections and removable panels;
provide flexible bonds where hinges alone are not a reliable path;
bond breaker trucks/removable parts through the manufacturer-designed sequence;
coordinate cable screens, glands, sealing ends and test links with protection/EMC design;
bond VT, surge-arrester and transformer enclosures and neutral equipment;
avoid paint, corrosion, loose hardware or dissimilar-metal interfaces in the fault path;
record maximum permissible resistance/drop for lifecycle continuity tests;
ensure temporary protective earth points connect to the intended grid path.

10. Fences, gates and the grid edge

Fence design is a boundary decision: include it in the grid, isolate it, or use a deliberately engineered hybrid according to the adopted method and local rules. Bonding a fence can transfer GPR along it; isolating it can leave hazardous potential differences across gates or services. Model a person touching the fence from outside, gate swing positions, vehicle contact, buried fence posts, CCTV/security cabling and adjacent public areas.

11. Transferred potential

LV neutral and protective conductor leaving the substation;
telecom copper and control multicore screens;
metallic water/fire pipes, gas lines and structural steel;
rail tracks, conveyors and security fences;
cable sheaths bonded at remote substations;
temporary construction supplies and portable-generator earths.

Mitigation may include insulating sections, optical communications, isolation transformers, coordinated neutral arrangements, sheath sectionalization or local gradient control. Each measure must be reviewed for protection, EMC, lightning, corrosion and regulatory consequences.

12. Conductor sizing and permanent connections

thermal withstand for current, duration and initial/final material temperature;
electrodynamic forces and mechanical damage at bends/connections;
minimum mechanical cross-section for construction and settlement;
soil chemistry, moisture, stray DC and galvanic corrosion;
compatibility of copper, galvanized steel, aluminum and stainless components;
allowance for corrosion over intended service life;
exothermic, compression, bolted or welded connection qualification;
installation tooling, operator competence and inspection evidence;
IEEE 837-2024 qualification for relevant permanent substation connections.

A low-resistance new joint is not proof of lifetime fault performance. Specify material combinations, preparation, installation process and mechanical/current-temperature/corrosion/fault-current evidence.

13. Power frequency versus lightning/high frequency

An AC grounding grid optimized for 50/60 Hz safety is not automatically an adequate lightning earth-termination design. At high frequency, inductance, conductor length, bends and wave propagation dominate. Coordinate IEC 61936-1 power-frequency safety with the applicable lightning-protection and insulation-coordination standards; do not substitute a lightning electrode reading for the substation GPR/touch study.

14. Design calculation workflow

freeze applicable standards, exposure locations and acceptance criteria;
survey soil and site metallic infrastructure;
calculate fault currents, current split and primary/backup durations;
select material, conductor cross-section and preliminary grid geometry;
build the soil/grid model and calculate Zg/GPR;
calculate touch, mesh, step and transferred potentials at hotspots;
compare each exposure with the corresponding permissible limit;
apply mitigation and rerun seasonal/topology/parameter sensitivities;
check conductor, connection, corrosion and constructability requirements;
issue drawings, test plan, assumptions and change-control triggers;
independently review the model and reconcile as-built changes.

15. Commissioning and field measurements

Test	Purpose	Typical risk/error to control
Soil resistivity	Validate design soil model	Buried metal, insufficient spacing, seasonal bias
Continuity/integrity	Find missing/damaged bonds and joints	Parallel paths hiding a defective connection
Ground impedance	Validate Zg at power frequency	Remote-electrode distance, mutual coupling and noise
Current distribution	Validate split among grid, shields/screens and neutrals	Unrepresentative injection path or topology
Touch/step profile	Validate surface potential at critical locations	Unsafe test currents, incorrect foot/contact electrode model
Visual/as-built	Confirm geometry, material and connections	Buried work inaccessible after completion

IEEE 81-2025 emphasizes measurement safety, instrumentation limitations and factors that distort results. Prepare a test risk assessment, injection/control scheme, communications plan and exclusion zone; test leads and remote probes can themselves create hazardous transferred potentials.

16. Interpreting test discrepancies

compare measured and modeled topology, frequency and soil moisture;
check remote probe placement and fall-of-potential curve quality;
identify parallel metallic return paths;
evaluate instrument noise rejection and utility-frequency interference;
reconcile as-built conductor/rod depth and missing bonds;
do not “tune” soil resistivity solely to force agreement;
update the model and repeat critical surface-potential checks;
record measurement uncertainty and acceptance rationale.

17. Lifecycle inspection and change triggers

utility or generation fault-level change;
relay/breaker clearing-time or protection-zone change;
overhead line replaced by cable, screen-bonding change or new interconnection;
new building, switchgear lineup, transformer, fence, road or buried service;
surface-layer deterioration, flooding, excavation or soil treatment;
corrosion, theft, damaged flexible bond or hot/loose joint;
lightning event, major fault, construction incident or unexplained shock/tingle;
standard revision or asset-owner review interval.

18. Common mistakes

accepting one resistance value as the safety criterion;
using total earth-fault current as grid current without current-split analysis;
checking primary clearing only;
using a single uniform soil value from one short-spacing test;
copying tolerable voltages from another project;
ignoring gates, fences, remote services and transferred potential;
assuming crushed rock remains dry/clean/high-resistivity forever;
allowing parallel bonds to mask a failed connection during continuity testing;
claiming IEEE P80 is a published replacement standard;
using the superseded IEEE 81-2012 when the contract calls for the current edition;
mixing power-frequency and lightning performance claims.

Minimum design dossier

applicable-standard/edition matrix and acceptance criteria;
soil raw data, interpretation and seasonal sensitivity;
fault-current, X/R, current-split and clearing-time cases;
grid model, GPR and touch/step/transferred-potential maps;
material, thermal, mechanical and corrosion calculations;
earthing/bonding drawings, details and connection specifications;
fence, cable-screen, neutral and external-service decisions;
construction inspection/hidden-work records;
commissioning method, calibration, raw results and uncertainty;
as-built model, exceptions, maintenance plan and change triggers.

Primary references

Safety note: Earthing design and high-current/ground-injection testing can create lethal potential differences. Qualified engineers and authorized test personnel must apply governing law, standards, owner rules and a site-specific risk assessment.

Earthing Systems, Touch Voltage and Step Voltage in Substations