What Is Grounding Resistance Testing and Why Is It Mandatory in Türkiye?

Grounding resistance testing is a periodic safety measurement that verifies how low the resistance is between an electrical installation's grounding system and the earth, and confirms the continuity of its protective conductors. Outside North America, the same practice is often called earthing testing. Its purpose is to prove numerically that, in the event of leakage or a fault, current can be safely discharged to ground before a dangerous touch voltage develops.

In practice, grounding testing examines two main quantities: grounding resistance (the resistance of the ground electrode to earth, in ohms) and protective conductor continuity (an unbroken connection from equipment enclosures to the main grounding busbar). Together, these two values show whether people are protected from electric shock and equipment from overvoltage.

In short, grounding testing is the engineering test that documents whether an invisible protection, one on which life and property directly depend, is actually working. In Türkiye, it is a legal requirement for this testing to be carried out and reported by authorized persons.

Grounding testing is mandatory because grounding is the first line of defense in an electrical installation, and only measurement can prove that it works. When an insulation fault occurs between a phase conductor and an equipment enclosure, the leakage current reaching the enclosure must flow to ground through a low-resistance path; this keeps the enclosure voltage from rising to a dangerous level until the protective device (fuse or residual current device) opens the circuit. If grounding resistance is high, this mechanism fails, and anyone who touches the enclosure is exposed to electric shock.

In Türkiye, the inspection of grounding installations is governed by the Regulation on Grounding in Electrical Installations (Elektrik Tesislerinde Topraklamalar Yönetmeliği) and is the responsibility of the workplace or facility owner. In addition, Turkish occupational health and safety (OHS) legislation explicitly requires grounding measurements as part of the periodic inspection of work equipment. Failing to test is not only a safety risk but also a deficiency that leads to administrative sanctions and liability during inspections.

Another dimension of the requirement is the burden of proof. After a workplace accident, fire or equipment damage, only an up-to-date measurement report signed by authorized persons can prove that the facility's grounding was adequate. Grounding testing is therefore both a technical necessity and a legal safeguard.

The most common method is the three- or four-pole fall-of-potential test performed with a ground resistance tester. In this method, the instrument uses two auxiliary electrodes (current and potential probes) driven into the ground in addition to the main ground electrode; it injects a known current into the soil and calculates the resistance from the resulting voltage difference. Placing the probes at the correct spacing and in the correct line is critical to the accuracy of the result.

In urban or concrete-floored facilities where auxiliary electrodes cannot be driven, the clamp-on method is used. This method measures loop resistance with a clamp placed around the grounding conductor and allows quick checks where many ground electrodes are connected in parallel. When soil resistivity, meaning how conductive the soil structure is, needs to be determined, the four-pole Wenner method is preferred; this measurement is essential, especially when designing a new grounding grid.

All of these measurements share the same requirements: calibrated instruments, suitable weather and ground conditions, and competent personnel. Because readings are sensitive to soil moisture, season and electrode placement, the measurement conditions should be recorded in the report and the test should be repeatable.

There is no single universal value for grounding resistance; the acceptance criterion depends on the type of installation, the voltage level and how the protection system operates. In low-voltage consumer installations, grounding must be low enough for the protective device in use (a residual current device or overcurrent protection) to trip within a safe time at the fault current, which is why the assessment is always made together with protection coordination.

In medium-voltage transformer substations and large industrial facilities, the grounding grid is designed to keep the step and touch voltages that arise during a fault within limits that are safe for people. Here, the decisive factor is not a low resistance value on its own but the calculated voltage distribution across the entire grounding grid. Separate, and generally lower, resistance targets also apply to the grounding of lightning protection systems.

The right approach, therefore, is to compare the measured value not against a memorized limit but against the criterion that the relevant regulations and standards set for that specific installation. For the report to be valid, the person interpreting the limits should have electrical engineering competence.

In industrial facilities, grounding and continuity checks are generally performed annually, while portable (non-fixed) equipment requires more frequent checks, typically every six months. Measurements are repeated periodically because ground electrodes corrode over time, connections loosen, and the moisture and conductivity of the soil change with the seasons. The regulations set different inspection intervals depending on the type of installation.

In addition to periodic testing, grounding must be re-measured when a new installation is commissioned, when the facility is modified or extended, and after a major fault or a lightning strike. Because these events can compromise the physical integrity of the grounding system, testing without waiting for the scheduled date is the right approach from a safety standpoint.

Measurement results should be recorded with the date, measurement conditions and values. Comparing results year over year makes it possible to spot early warning signs such as a gradual rise in grounding resistance, allowing preventive maintenance before major failures occur.

Miratek Elektrik handles grounding design, installation and verification measurements as a single package, from 1–35 kV medium-voltage systems to low-voltage installations. In our transformer substation projects, the grounding grid, protection relay coordination and commissioning tests are planned together, so the measurement is not a formality but a genuine verification of the facility's actual safety status.

Our field experience in lightning protection and grounding system design, commissioning tests and relay coordination allows us to interpret measurement results correctly and, where non-conformities are found, to offer grounding improvement solutions within the same team. All of our processes are carried out under ISO 9001:2015, ISO 14001:2015 and ISO 45001:2018 management systems.

With 15+ years of experience and 1,300+ completed projects, our team serves clients across Türkiye, providing grounding testing, reporting and full standards-compliance support for industrial facilities, organized industrial zones (OIZs), solar power plants (SPPs) and transformer substations. Contact the Miratek Elektrik engineering team for a grounding inspection or improvement at your facility.