The field problem
Marine Earthing System for a Transformer Installed on a Coastal Bridge
field problem / engineering challenge
A transformer was installed on a coastal bridge to supply remote cabins within the water. With no conventional direct soil contact beneath the transformer, the design had to address earthing, touch and step voltage control, marine corrosion, equipotential bonding, fault-current withstand and lightning protection.
engineering analysis
The fault-current path must be deliberately engineered. Seawater alone should not be assumed to be the earthing electrode. The review should consider GPR, touch/step voltages, accessible metallic parts, bonding, conductor and connection durability, corrosion, cathodic-protection coordination where applicable, lightning-current paths, inspection and maintenance.
Why it failed
Engineering Analysis
The fault-current path must be deliberately engineered. Seawater alone should not be assumed to be the earthing electrode. The review should consider GPR, touch/step voltages, accessible metallic parts, bonding, conductor and connection durability, corrosion, cathodic-protection coordination where applicable, lightning-current paths, inspection and maintenance.
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 an integrated earthing, bonding, fault-current, corrosion-control and lightning-protection system with long-term maintainability.
Correction & verification
WRONG - Treat marine grounding as conventional grounding placed over water, or rely on seawater alone.
CORRECT - Engineer an integrated earthing, bonding, fault-current, corrosion-control and lightning-protection system with long-term maintainability.
Marine grounding is not simply conventional grounding placed over water. It is a complete engineering discipline that combines earthing, corrosion control, equipotential bonding, fault-current withstand, and long-term reliability.
Verification recorded in the case
- Record as-built topology and connection points.
- Repeat the measurement or functional test under a defined condition.
- Confirm continuity and mechanical integrity of the corrected path.
- Document instrument/setup, environmental condition and test method.
- Close the case only when evidence supports the conclusion.
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-021
View the original social cardThe engineering lesson
Marine grounding is not simply conventional grounding placed over water. It is a complete engineering discipline that combines earthing, corrosion control, equipotential bonding, fault-current withstand, and long-term reliability.
Take the lesson into your next design review.