The field problem
Hospital — Sheikh Zayed
A so-called clean-earthing arrangement relied on the soil path between separated points to complete the return path.
why the obvious answer can be misleading
Soil impedance is variable and cannot provide the predictable low-impedance metallic fault-return path required for protective bonding. Performance changes with resistivity, moisture and geometry.
Why it failed
Soil impedance is variable and cannot provide the predictable low-impedance metallic fault-return path required for protective bonding.
Performance changes with resistivity, moisture and geometry.
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
Provide a continuous engineered protective/bonding conductor between the relevant points, coordinated with the supply earthing arrangement and protection scheme.
Correction & verification
Provide a continuous engineered protective/bonding conductor between the relevant points, coordinated with the supply earthing arrangement and protection scheme.
Functional/clean-earth requirements must not defeat protective bonding.
Verification recorded in the case
- Verify continuity and automatic-disconnection conditions after the metallic path is established.
- 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 NCR/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.
IEC 60364-4-41 and IEC 60364-5-54.
PIS reviewed field handbook · PIS-CS-010
View the original social cardThe engineering lesson
Functional earthing must never be achieved by weakening protective earthing.
Take the lesson into your next design review.