Advanced Resistance Testing

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The single most important number on any lightning protection or earthing system is its resistance to earth. If that number is too high, the system will not function, no matter how well it was designed or how carefully it was installed. Resistance testing is the proof that your system works.

HHK provides advanced resistance testing using calibrated, professional-grade equipment and methodologies that go well beyond a simple stick-two-rods-in-the-ground approach. Our testing teams are trained in multiple methods, understand the limitations of each, and select the right technique for the specific site conditions.

Testing Methods We Use:

Fall-of-Potential Method (62% Rule)

The gold standard for earth resistance measurement, specified in SANS 10199 and IEEE 81. A test current is injected through the electrode under test and a remote current probe, while the voltage rise is measured at increasing distances from the electrode.

By plotting resistance against distance, we identify the true earth resistance, excluding the influence of the test probes themselves. The method is accurate, repeatable, and accepted by all regulatory bodies.

Soil Resistivity Testing (Wenner Method)

This measures the electrical resistivity of the soil itself, which is the fundamental parameter that determines earth electrode performance. We use it both for new system designs and for diagnosing why an existing electrode is not performing as expected.

Clamp-On / Stakeless Testing

On built-up urban sites, paved surfaces, or anywhere driving test probes is impractical, we use clamp-on earth testers that measure resistance without disconnecting the electrode or driving auxiliary probes.

The method has limitations: it cannot be used on isolated electrodes. But for multi-grounded systems, it provides rapid, non-invasive measurements.

Selective Testing

A variation of the fall-of-potential method that allows measurement of a single electrode within a parallel earth network without disconnecting it. This is critical for testing substation grids, tower earthing, and interconnected building systems where isolation is not practical.

High-Frequency / Impulse Testing

For specialist applications, particularly lightning protection itself, standard DC or low-frequency resistance measurements do not tell the full story.

Under lightning conditions, with fast rise times and high frequencies, the impedance of an earthing system can differ significantly from its DC resistance. Inductive effects in long conductors and soil ionisation around electrodes both come into play.

Our impulse testing capability measures the actual transient impedance your system presents to a lightning strike.

Interpreting Test Results

A resistance reading on its own tells you very little. What matters is context:

How the reading compares against the design target (typically ≤10 Ω for lightning protection per SANS 62305-3, but often lower for sensitive equipment)
How it has changed over time, because trend analysis reveals degradation before it becomes critical
Whether seasonal variation is being accounted for, since soil resistivity fluctuates with moisture and temperature
Whether the measurement method was appropriate for the specific electrode configuration
What the reading means in the context of the site’s soil resistivity, because a seemingly “high” resistance may actually be the best achievable for those soil conditions

Our Testing Equipment

All HHK resistance testing is conducted using professional-grade, regularly calibrated instruments from leading manufacturers. Our equipment handles 3- and 4-terminal measurements, covers resistance ranges from milliohms to kilo-ohms, and operates reliably in the field conditions that characterise many of our project sites across Southern Africa: heat, dust, and rough terrain.

Testing You Can Trust

Resistance testing is not a commodity service. The difference between a competent test and a meaningless one comes down to method, equipment, training, and experience. HHK’s testing teams bring all four, backed by nearly 50 years of earthing and lightning protection practice across every soil type and site condition Southern Africa has to offer.

When we test your system, we are not just checking a box. We are verifying that the protection you have invested in will actually work when it is needed.

When Advanced Testing Is Required

Commissioning of new lightning protection and earthing installations (acceptance testing)
Periodic maintenance inspections as required by SANS 62305-3
After any lightning strike to a protected structure, to verify system integrity
Before issuing or renewing a Certificate of Compliance
When earth resistance values from previous tests show an increasing trend
For insurance assessments, compliance audits, and ISO accreditation
During property transactions, as part of technical due diligence
When adding new equipment or expanding an existing electrical installation

Every HHK installation includes a full test report and a legally recognised Certificate of Compliance — essential for insurance purposes and regulatory audits.

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What Makes HHK the right choice for Advance Resistance Testing