The field problem
The Hidden Failure of Grounding Connections - Hurghada MV Substation
timeline of failure
Initial commissioning: Earth Resistance ≈ 1 Ω. The system appeared to pass commissioning.
After approximately three months: Earth Resistance increased to ≈ 11 Ω, despite no reported modification to the grounding network.
engineering investigation
The progressive deterioration was traced to the connection system rather than simply to the bulk soil or the measuring instrument.
Why it failed
Timeline of Failure
Initial commissioning: Earth Resistance ≈ 1 Ω. The system appeared to pass commissioning.
After approximately three months: Earth Resistance increased to ≈ 11 Ω, despite no reported modification to the grounding network.
Engineering Investigation
The progressive deterioration was traced to the connection system rather than simply to the bulk soil or the measuring instrument.
Root Cause 1 — Dissimilar Metals
The connection combined an aluminium conductor, a copper-bonded steel rod, and a bronze/brass clamp.
In the presence of moisture, salts and the coastal environment, the dissimilar-metal interface created a galvanic-corrosion risk. The connection therefore became a long-term reliability weak point even though the initial resistance result was good.
Root Cause 2 — Improper Clamp Selection
The clamp was not suitable for the transition between the different metals.
The failure chain identified in the original engineering review was: increasing contact resistance → corrosion → local heating → further resistance increase → progressive deterioration of the connection and grounding performance.
Follow the engineering
Switch between the field condition and the engineering concept. Trace the path and examine what changes.
Inspect the engineering detail
What changes
Engineer the metallic transition, use a compatible/approved connector, apply the specified installation torque, protect against the actual environment, verify after repair, and periodically inspect/trend the connection condition.
Correction & verification
Replace the unsuitable transition with an approved connector/clamp specifically suitable for the dissimilar metals involved — for example, a properly selected bimetallic or otherwise material-compatible connection system.
Do not treat the clamp as a generic accessory. Verify conductor/electrode material compatibility, connector rating, environmental suitability and corrosion behaviour.
Install and tighten the connection using a calibrated torque wrench to the manufacturer-specified torque. Both under-torque and over-torque are unacceptable: insufficient torque can create a high-resistance/loose interface, while excessive torque can damage the connector or conductor and compromise long-term integrity.
Use approved clamp/connector materials and installation details suitable for the coastal environment and the actual conductor/electrode combination.
After corrective work, re-test the grounding system and use the new result as a baseline for periodic trending.
Introduce periodic inspection of critical grounding connections for corrosion, loosening, mechanical deterioration and abnormal resistance increase.
Visual and mechanical inspection of the repaired transition.
Confirmation of connector type and material compatibility.
Verification that installation torque matches the manufacturer requirement.
Earth-resistance measurement after corrective work using an appropriate test method.
Periodic comparison against the post-repair baseline.
Re-inspection if resistance trends upward, corrosion becomes visible, or the connection shows mechanical deterioration.
Verification recorded in the case
- Visual and mechanical inspection of the repaired transition.
- Confirmation of connector type and material compatibility.
- Verification that installation torque matches the manufacturer requirement.
- Earth-resistance measurement after corrective work using an appropriate test method.
- Periodic comparison against the post-repair baseline.
- Re-inspection if resistance trends upward, corrosion becomes visible, or the connection shows mechanical deterioration.
References & project context
References are reproduced from the PIS casebook. Select the governing edition and project acceptance criteria before using them for a design. The diagrams explain the concept, rather than define construction dimensions.
Apply the contract-specified IEC/IEEE/NFPA/local framework relevant to the actual project scope. Verify exact editions and clauses before external publication.
PIS reviewed field handbook · PIS-CS-002
View the original social cardThe engineering lesson
A grounding system is only as reliable as its weakest connection.
A good commissioning resistance value proves the system at that moment; it does not prove that an incompatible or poorly installed metallic connection will remain reliable for years.
Grounding reliability depends not only on electrode resistance, but also on connection technology, material compatibility, installation torque, corrosion control and maintenance.
Take the lesson into your next design review.