The field problem
New Minya — Rocky Site
Fall-of-Potential testing repeatedly returned open-loop/no valid reading in a rocky area.
why the obvious answer can be misleading
A large buried high-resistivity rock mass near the auxiliary-electrode zone prevented a useful test-current return path. The problem was the test environment, not necessarily a broken main earth electrode.
Why it failed
A large buried high-resistivity rock mass near the auxiliary-electrode zone prevented a useful test-current return path.
The problem was the test environment, not necessarily a broken main earth electrode.
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
Change the test direction and auxiliary-electrode zone, increase separation as necessary, and establish a valid current circuit before interpreting resistance.
Correction & verification
Change the test direction and auxiliary-electrode zone, increase separation as necessary, and establish a valid current circuit before interpreting resistance.
Verification recorded in the case
- Confirm that the instrument can inject current and that repeat readings are stable from a suitable direction.
- 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.
Earth-resistance test methodology; IEC 61557-5 principles.
PIS reviewed field handbook · PIS-CS-005
View the original social cardThe engineering lesson
An instrument error message must be diagnosed electrically and geologically before it is treated as a system failure.
Take the lesson into your next design review.