The field problem
Industrial Complex — 10th of Ramadan
Several earthing systems achieved resistance values better than their specified targets, yet abnormal behaviour appeared later.
why the obvious answer can be misleading
Review showed that the conductor network’s fault-current/thermal duty was lower than the prospective duty expected at the installation. Earth resistance alone therefore did not prove that the network could survive a fault event.
Why it failed
Review showed that the conductor network’s fault-current/thermal duty was lower than the prospective duty expected at the installation.
Earth resistance alone therefore did not prove that the network could survive a fault event.
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
Check conductor cross-section and connections against prospective fault current and clearing time, not only the final resistance target.
Correction & verification
Check conductor cross-section and connections against prospective fault current and clearing time, not only the final resistance target.
Locate and repair any damaged high-current path.
Verification recorded in the case
- Perform continuity and low-resistance checks after repair and verify the thermal/fault-duty calculation.
- 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 60364-5-54; applicable substation/fault-current design requirements.
PIS reviewed field handbook · PIS-CS-017
View the original social cardThe engineering lesson
An earthing system must both dissipate voltage and survive the current that creates it.
Take the lesson into your next design review.