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PIS-CS-004/Measurement

The grid was blamed. The test was wrong.

The earth grid was blamed. The test geometry was wrong.

Upper EgyptEducation3 min read
Fall-of-Potential test geometryEngineered approach for PIS-CS-004. Extend the line outside the relevant influence zone. Move the potential probe around the justified test position. Look for a defensible stable region; extend or change method if absent. Conceptual teaching detail, not an as-built drawing or construction instruction. © PIS Engineering Academy · All rights reserved.PIS ENGINEERING / CASE 004Fall-of-Potential test geometryENGINEERED APPROACHVERIFYEARTH TESTEREPCPCEXTEND BEYOND INFLUENCEConfirm the curve around the justified potential-probe position.SCHEMATIC TEST CURVE1231Extend the line outside therelevant influence zone.2Move the potential probearound the justified testposition.3Look for a defensible stableregion; extend or changemethod if absent.READ THE DETAILEquipment, joints and current-path interfaces are shown in context.Conceptual teaching plate · no project dimensions or acceptance limits impliedPIS / REV 03© PIS Engineering Academy · All rights reserved

Engineering concept / vector field note

01

The field problem

School — Upper Egypt

Final earth-resistance readings changed repeatedly during handover.

why the obvious answer can be misleading

The technician used a short test span and did not place the potential probe according to the intended Fall-of-Potential geometry. The auxiliary electrodes remained too close to the system influence zone, so movement of the probes changed the measured result.

02

Why it failed

The technician used a short test span and did not place the potential probe according to the intended Fall-of-Potential geometry.

The auxiliary electrodes remained too close to the system influence zone, so movement of the probes changed the measured result.

03

Follow the engineering

Switch between the field condition and the engineering concept. Trace the path and examine what changes.

Inspect the engineering detail

Fall-of-Potential test geometryEngineered approach for PIS-CS-004. Extend the line outside the relevant influence zone. Move the potential probe around the justified test position. Look for a defensible stable region; extend or change method if absent. Conceptual teaching detail, not an as-built drawing or construction instruction. © PIS Engineering Academy · All rights reserved.PIS ENGINEERING / CASE 004Fall-of-Potential test geometryENGINEERED APPROACHVERIFYEARTH TESTEREPCPCEXTEND BEYOND INFLUENCEConfirm the curve around the justified potential-probe position.SCHEMATIC TEST CURVE1231Extend the line outside therelevant influence zone.2Move the potential probearound the justified testposition.3Look for a defensible stableregion; extend or changemethod if absent.READ THE DETAILEquipment, joints and current-path interfaces are shown in context.Conceptual teaching plate · no project dimensions or acceptance limits impliedPIS / REV 03© PIS Engineering Academy · All rights reserved

Case 004 · Engineered approach

100%
Fall-of-Potential test geometryEngineered approach for PIS-CS-004. Extend the line outside the relevant influence zone. Move the potential probe around the justified test position. Look for a defensible stable region; extend or change method if absent. Conceptual teaching detail, not an as-built drawing or construction instruction. © PIS Engineering Academy · All rights reserved.PIS ENGINEERING / CASE 004Fall-of-Potential test geometryENGINEERED APPROACHVERIFYEARTH TESTEREPCPCEXTEND BEYOND INFLUENCEConfirm the curve around the justified potential-probe position.SCHEMATIC TEST CURVE1231Extend the line outside therelevant influence zone.2Move the potential probearound the justified testposition.3Look for a defensible stableregion; extend or changemethod if absent.READ THE DETAILEquipment, joints and current-path interfaces are shown in context.Conceptual teaching plate · no project dimensions or acceptance limits impliedPIS / REV 03© PIS Engineering Academy · All rights reserved

Scroll to inspect. Numbered details match the notes below the drawing. Conceptual geometry; use the case text for the engineering requirements.

What changes

Re-establish the test line outside the electrode influence zone, use the applicable Fall-of-Potential/62% procedure for the electrode geometry, and confirm the result by moving the potential probe around the nominal point rather than relying on one reading.

Teaching schematic · not to scale© PIS Engineering Academy · All rights reserved
04

Correction & verification

Re-establish the test line outside the electrode influence zone, use the applicable Fall-of-Potential/62% procedure for the electrode geometry, and confirm the result by moving the potential probe around the nominal point rather than relying on one reading.

Verification recorded in the case

  • A valid result should show a sufficiently stable region around the selected potential-probe position. If the curve does not stabilise, extend the test distance or change method.
  • 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 61557-5; accepted earth-resistance test methodology; instrument manufacturer guidance.

PIS reviewed field handbook · PIS-CS-004

View the original social card
05

The engineering lesson

Before redesigning an earth grid, prove that the measurement itself is valid.

Take the lesson into your next design review.

Keep exploring

Connected lessons.

All cases
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01

Measurement

Soil resistivity & rod spacing

Never Trust One Soil Resistivity Test.

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A rock mass interrupts the test circuitEngineered approach for PIS-CS-005. Change test direction and place auxiliary probes in suitable ground. Increase separation as required to establish the injection circuit. Confirm injection and repeatability before interpreting resistance. Conceptual teaching detail, not an as-built drawing or construction instruction. © PIS Engineering Academy · All rights reserved.PIS ENGINEERING / CASE 005A rock mass interrupts the test circuitENGINEERED APPROACHVERIFYEARTH TESTEREPCPCBURIED ROCK MASSChange the test direction to establish an injection circuit.1231Change test direction andplace auxiliary probes insuitable ground.2Increase separation asrequired to establish theinjection circuit.3Confirm injection andrepeatability beforeinterpreting resistance.READ THE DETAILEquipment, joints and current-path interfaces are shown in context.Conceptual teaching plate · no project dimensions or acceptance limits impliedPIS / REV 03© PIS Engineering Academy · All rights reserved
05

Measurement

An open loop in rocky ground

OPEN LOOP did not mean an open earthing system.

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Solar trackers, geology and the measurement objectiveEngineered approach for PIS-CS-006. Profile soil depth and select electrode arrangements from evidence. Use the test method appropriate to isolated or interconnected topology. Verify tracker bonding and correlate measurements with control behaviour. Conceptual teaching detail, not an as-built drawing or construction instruction. © PIS Engineering Academy · All rights reserved.PIS ENGINEERING / CASE 006Solar trackers, geology and the measurement objectiveENGINEERED APPROACHTRACKERARRAY STRUCTURE / TRACKER DRIVE / CONTROL INTERFACESSoil model, test topology and control behaviour are separate checks.1231Profile soil depth and selectelectrode arrangements fromevidence.2Use the test methodappropriate to isolated orinterconnected topology.3Verify tracker bonding andcorrelate measurements withcontrol behaviour.READ THE DETAILEquipment, joints and current-path interfaces are shown in context.Conceptual teaching plate · no project dimensions or acceptance limits impliedPIS / REV 03© PIS Engineering Academy · All rights reserved
06

Measurement

Solar earthing & tracker control

One test method cannot describe every part of a solar plant.

Benban, Aswan3 min
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