IEEE 81-2025 IEEE Guide for Measuring Earth Resistivity, Ground Impedance, and Earth Surface Potentials of a Grounding System

About this publication

The IEEE 81-2025 IEEE Guide for Measuring Earth Resistivity, Ground Impedance, and Earth Surface Potentials of a Grounding System is a major technical reference for electrical engineers, substation engineers, grounding specialists, utilities, testing organizations, commissioning teams, consultants, and safety professionals responsible for evaluating the condition, effectiveness, and electrical performance of grounding systems.

Published by IEEE and developed under the IEEE Power & Energy Society Substations Committee, this guide presents practical test methods and measurement techniques for determining key electrical characteristics of grounding systems. It is specifically intended to help professionals measure soil resistivity, grounding-system impedance, ground resistance, transient performance, and earth-surface potentials using recognized and repeatable testing practices.

A central purpose of IEEE 81 is to provide practical methods for determining earth electrical resistivity before or during grounding-system design and for evaluating completed grounding systems after installation. Soil resistivity directly affects grounding-grid performance, electrode design, ground potential rise, and the ability of a grounding system to safely dissipate fault and surge currents. Accurate field measurements therefore play an important role in both system design and safety verification.

The guide also addresses measurement of the power-frequency resistance or impedance of a grounding system to remote earth. These measurements are critical when evaluating substations, industrial electrical facilities, generating facilities, transmission installations, and other locations where grounding-system performance can directly affect personnel safety and equipment protection.

Another major area covered by IEEE 81-2025 is the measurement of step and touch voltages. During an electrical fault, voltage gradients can develop across the surface of the earth around grounding systems. Measuring these potentials helps engineers determine whether personnel may be exposed to hazardous voltage differences while standing near grounded equipment or simultaneously touching grounded structures.

The standard also provides guidance for measuring transient or surge impedance, helping professionals evaluate how a grounding system behaves during rapidly changing conditions such as lightning impulses and other transient events. This makes IEEE 81 valuable not only for conventional grounding studies but also for facilities where lightning protection, surge behavior, and transient grounding performance are significant engineering concerns.

IEEE 81-2025 goes beyond simply describing individual test methods. It also addresses safe testing conditions, grounding-system integrity verification, instrumentation characteristics and limitations, common ground-testing procedures, and factors that can distort measurement results. These issues matter enormously in field work, where nearby energized systems, interconnected conductors, buried metallic structures, overhead ground wires, soil conditions, test lead placement, and instrument limitations can all influence results.

The 2025 revision replaces IEEE 81-2012, making it the current IEEE guide for this subject. For utilities and engineering firms still relying on the previous edition, IEEE 81-2025 provides the current reference for developing test procedures, training personnel, conducting commissioning tests, investigating grounding problems, and documenting grounding-system performance.

At approximately 169 pages, IEEE 81-2025 is a substantial working guide rather than a brief overview. For organizations responsible for substations, power distribution systems, industrial electrical installations, or high-voltage equipment, it belongs alongside grounding-system design standards as an important field-measurement and verification reference.

Why This Standard Matters

IEEE 81-2025 is particularly valuable for professionals who need to verify that grounding systems actually perform as intended in the field. It is especially relevant for:

• Electrical and power-system engineers

• Substation engineers and designers

• Grounding and lightning-protection specialists

• Electric utilities and generating facilities

• Industrial electrical facilities

• Field-testing and commissioning organizations

• Electrical safety and compliance professionals

• Engineering consultants

• Maintenance and reliability teams

• Technical and utility standards libraries

Product Features

• Current IEEE 81-2025 active standard

• Supersedes IEEE 81-2012

• Presents practical methods for grounding-system testing and measurement

• Covers measurement of earth electrical resistivity

• Addresses ground resistance and ground impedance to remote earth

• Covers power-frequency grounding-system impedance

• Includes methods for measuring transient and surge impedance

• Addresses step and touch voltage measurements

• Supports evaluation of ground potential and personnel exposure

• Includes procedures for verifying grounding-system integrity

• Reviews common methods for performing field ground testing

• Discusses instrumentation characteristics and limitations

• Addresses factors that may distort or influence test measurements

• Includes important testing safety considerations

• Applicable to substation, utility, industrial, and other electrical grounding systems

• Developed under the IEEE Power & Energy Society Substations Committee

Product Details

Title: IEEE 81-2025 IEEE Guide for Measuring Earth Resistivity, Ground Impedance, and Earth Surface Potentials of a Grounding System
Publisher: IEEE
Standard: IEEE 81-2025
Status: Active Standard
Published: July 15, 2026
Number of Pages: 169
Standard Committee: IEEE Power & Energy Society — Substations Committee
Working Group: Grounding System Measurements in Substations
Supersedes: IEEE 81-2012