Soil Resistance Measurement
Short answer: Soil resistance measurement is a test that determines the resistance of the grounding system to the ground in ohms; the most common method is the three-point (falling potential) method. In newer designs, the specific resistance of the soil is measured using the Wenner four-electrode method.
Grounding is the invisible but most critical component of electrical safety. It can only safely conduct leakage current to the ground in the event of a fault if it has a sufficiently low resistance. This resistance is not visually detectable; it can only be determined by measurement with a calibrated device.
High ground resistance can cause protection devices to fail to trip in time during a fault, leading to dangerous touch voltages. Regular measurement is vital because corrosion, drying ground, and loose connections increase resistance over time.
What is involved in measuring soil resistance?
- Measurement of grounding resistance using the three-point (falling potential) method.
- Soil resistivity using the Wenner method (for design purposes)
- Correct positioning of the auxiliary electrodes.
- Factors such as season and soil moisture should be evaluated.
- Interpretation of results according to system type and standard.
- Condition of grounding electrode and connections
Correctly Interpreting Measurement Results
The value obtained from a soil resistance measurement is not, by itself, 'good' or 'bad'; the correct interpretation depends on the purpose of the installation. While lightning protection grounding generally aims for 10 ohms and below, in a system protected by a residual current device (RCD), the value is evaluated to ensure that the touch voltage remains below the safe limit. Furthermore, since the measurement shows seasonal variations depending on soil moisture, the value from the dry period should be considered. Therefore, interpreting the result correctly requires expertise as much as performing the measurement itself.
Legal Basis and Accurate Assessment
In workplaces, periodic inspections of grounding systems are generally carried out at least once a year and documented with a TÜRKAK accredited report. If the values are high, the number/depth of electrodes can be increased or ground improvement solutions can be applied.
Frequently Asked Questions
What should the ground resistance be in ohms?
It varies depending on the system type and purpose; in lightning protection, the target is generally ≤10 ohms, while in RCD systems, it is determined according to the touch voltage rule.
How often should measurements be taken?
It is generally recommended once a year in workplaces; more frequently on corrosive/unstable floors.
What should be done if the value is high?
The number/depth of electrodes is increased, connections and corrosion are checked, or a soil conditioner is applied.
Ensure your safety with accredited measurement.
For accredited measurement and control. Grounding Systems Please review our page for the legal framework. mandatory periodic inspection Check our guide.