Ground Resistance Fails to Meet Requirements? The Problem Often Lies at the Connection Between the Grounding Lead-Out Device and the Grounding System

When a grounding resistance test fails, the first reaction for many engineers is often to assume that there are not enough grounding electrodes or that they are not buried deep enough. As a result, additional grounding materials are installed in an attempt to reduce resistance.

However, experienced field engineers know that a significant number of grounding resistance failures are not caused by the grounding electrodes themselves, but rather by problems at the connection points between the grounding lead-out device and the grounding conductor or grounding grid. Located below ground level and difficult to inspect during acceptance, these connection points are often the most vulnerable parts of the entire grounding system.

1. Connection Resistance: A Hidden Cause of Grounding Failure

The connection between the grounding lead-out conductor and the grounding electrode or grounding grid is critical to system performance.

If the connection relies on mechanical methods such as bolting or compression joints, the initial resistance measurement may appear normal immediately after installation. However, underground environments contain moisture, oxygen, and electrolytes, which gradually accelerate oxidation on metal contact surfaces.

As oxidation layers build up, contact resistance increases.

Lightning current is a high-frequency transient pulse and is particularly sensitive to connection impedance. Poor-quality connections can generate intense localized heating during a lightning event. In minor cases, the joint may become overheated and damaged; in severe cases, the connection may completely fail.

A system may still show continuity during routine testing, but when an actual lightning strike occurs, that weak connection point may become the failure point of the entire grounding path.

2. Grounding Lead-Out Conductor Problems Can Also Increase Resistance

Another common issue is the grounding lead-out conductor itself.

Potential problems include:

• Insufficient conductor cross-sectional area

• Poorly treated intermediate joints

• Excessive bending causing internal conductor damage

• Inadequate connection protection

Any of these issues can increase resistance along the grounding path.

During total grounding resistance measurements, the resistance contribution from the lead-out section becomes part of the overall result. This can create a situation where grounding resistance remains high despite continuously adding more grounding electrodes.

In such cases, adding more grounding materials is ineffective. It is similar to increasing water flow upstream while the actual blockage remains downstream.

3. Incorrect Testing Methods Can Lead to Misdiagnosis

Grounding resistance measurement itself can sometimes produce misleading results.

Common testing problems include:

• Incorrect test lead arrangement

• Auxiliary electrodes placed too close together

• Test wires running alongside underground metal pipelines or structures

• External electromagnetic interference

These factors can distort measurement results and lead to incorrect conclusions.

During acceptance testing of grounding lead-out systems, auxiliary electrodes should be positioned away from interference sources. Multiple measurements from different directions are recommended to obtain reliable and stable values.

Seasonal conditions should also be considered. Ground resistance is often higher during dry seasons than during wet seasons. Therefore, evaluation should be based on the most unfavorable expected conditions rather than relying on the lowest resistance value measured during ideal weather conditions.

4. The Most Effective Troubleshooting Method: Section-by-Section Testing

A practical troubleshooting approach is to test the grounding system in sections.

The process is:

1. Disconnect the grounding lead-out device from the grounding grid or electrode.

2. Measure the resistance of the grounding electrode/grid separately.

3. Measure the resistance of the lead-out conductor separately.

4. Compare the two results to identify the problematic section.

In many real projects, the issue is concentrated at a single connection point. Replacing the connection using reliable methods such as exothermic welding can immediately reduce grounding resistance.

Even the highest-quality grounding materials cannot compensate for a weak connection point. A single unreliable joint can compromise the performance of the entire grounding system.

5. Do Not Add Materials Before Finding the Actual Problem

When grounding resistance exceeds the required value, blindly increasing the number of grounding rods or expanding the grounding grid is not always the correct solution.

Before any retrofit, engineers should carefully evaluate:

• Grounding electrode performance

• Connection quality

• Lead-out conductor size

• Joint protection measures

• Measurement accuracy

Identifying the true failure point is far more important than simply adding more materials.

6. Long-Term Monitoring Is More Important Than a Single Acceptance Test

Grounding performance should not be judged by a single measurement.

A reliable maintenance strategy should include:

• Testing during initial construction

• Testing after one year of operation

• Annual testing before the lightning season

Analyzing long-term trends is often more valuable than looking at one isolated measurement.

Some grounding systems may show excellent resistance values immediately after commissioning but experience a two- or three-fold increase after several years. In many cases, the cause is slow underground corrosion at connection points that cannot be identified through one-time testing.

The reliability of grounding lead-out systems is proven through continuous monitoring and trend analysis—not through a single acceptance measurement.

Conclusion

When grounding resistance fails to meet requirements, the first step should not be adding more grounding electrodes. The priority should be identifying whether the problem lies in:

• The grounding electrodes themselves

• The grounding lead-out conductor

• The connection points

• The testing method

By isolating and testing each section of the grounding path, the actual cause can be quickly identified and effectively corrected.

Before adding more grounding materials, determine where the real problem is. In many cases, the weakest point is not the grounding grid—it is the small connection hidden underground that determines the performance of the entire system.