Earthing / Lightning / Surge Troubleshooting

Equipment / System

Individual earth electrode, earth rod group, or the CCR/base-can earthing grid, as measured at the earth pit or test link.

Possible Causes

Required Tools

Safety Precautions

• De-energise and isolate associated equipment before working in the earth pit where practical.
• Treat all earth conductors as potentially carrying fault or lightning current — do not disconnect a sole earth path without an alternative in place.
• Be alert to buried services when opening earth pits.

Diagnostic Procedure

1. ObservationConfirm the test was performed correctly — correct method (fall-of-potential vs. clamp-on), correct probe spacing, and away from interfering buried metalwork or parallel earth paths.
2. MeasurementRepeat the test and compare against the site's historical readings and the original commissioning value to establish whether this is a genuine rise or a seasonal/test variation.
3. ObservationInspect the earth pit for electrode corrosion, broken bonding conductors, or physical disturbance.
4. DecisionReading confirmed genuinely elevated and no test-method explanation found → proceed to grid continuity testing (ELS-416) and consider soil treatment or supplementary electrodes. Reading explained by seasonal dryness and within seasonal historical range → log and re-test after the next wet period.
5. Root CauseDetermine whether the rise reflects a genuine degradation of the electrode/grid or a normal seasonal/environmental variation.

Test Points

Root Cause Verification

Re-test using the correct method after any corrective action, and confirm the reading is stable and within threshold across at least two independent measurements.

Corrective Action

• Add supplementary earth electrodes or extend the grid if the design margin is confirmed insufficient.
• Repair or replace a broken bonding conductor found in the grid.
• Apply soil treatment (e.g. earth enhancement compound) at electrodes in high-resistivity soil where supplementary electrodes are impractical.

Preventive Action

• Test earth resistance on a defined seasonal schedule (typically pre- and post-monsoon) and trend results rather than testing once a year at an arbitrary time.
• Maintain an accurate earthing/grounding as-built drawing showing every electrode and bonding connection.
• Flag sites with a history of marginal readings for supplementary electrode installation during the next major maintenance cycle.

Related References

SOP: SOP-ELS-01 (Earth Resistance Test Procedure), SOP-CCR-04 (CCR LOTO Procedure)

Standards: IEEE 80, IS 3043 (earthing code of practice), ICAO Annex 14 Vol I

Diagram: Earthing/Grounding As-Built Drawing

Case Study: Division 25 — Field Case Study Troubleshooting

Equipment / System

Equipment earth bonding conductor from the item in question back to the nearest earth grid connection point or electrode.

Possible Causes

Required Tools

Safety Precautions

• LOTO the associated circuit before working on equipment earthing.
• Do not assume equipment is safely earthed based on appearance alone — verify by test before working on or near it.

Diagnostic Procedure

1. ObservationIdentify the specific item of equipment reported or found with a suspect earth connection, and locate its bonding conductor on the as-built earthing schedule.
2. MeasurementTest continuity/resistance of the bonding conductor from the equipment to the nearest confirmed earth grid connection point.
3. ObservationInspect the bonding point at both ends for corrosion, paint/coating, looseness, or physical damage.
4. DecisionBonding conductor confirmed absent, damaged, or high-resistance → repair or reinstate the bond. Bonding conductor tests correctly despite the report → investigate whether the original report was based on a different cause (e.g. a nuisance earth-fault trip unrelated to this equipment's own bond).
5. Root CauseConfirm whether the poor bond was never correctly made, has degraded over time, or was disturbed during other work.

Test Points

Root Cause Verification

After repair, re-test the bonding conductor's continuity/resistance and confirm it meets the design requirement, and visually confirm a sound mechanical connection at both ends.

Corrective Action

• Reinstate or replace the missing or damaged bonding conductor.
• Clean bonding surfaces to bare metal before remaking the connection, and apply an appropriate anti-corrosion treatment after.
• Replace a damaged or missing earth stud/lug on the equipment.

Preventive Action

• Include equipment earth bond verification in the periodic maintenance cycle for all major AGL equipment items.
• Require earth bond verification as a mandatory step whenever equipment is relocated, replaced, or disturbed during other work.
• Maintain an accurate equipment earthing schedule cross-referenced to the main earthing drawing.

Related References

SOP: SOP-ELS-02 (Equipment Earth Bond Verification Procedure), SOP-CCR-04 (CCR LOTO Procedure)

Standards: IS 3043, IEC 60364, ICAO Annex 14 Vol I

Diagram: Equipment Earthing Schedule

Case Study: Division 01 — CCR Troubleshooting (cabinet earthing)

Equipment / System

Earth conductor between an electrode, bonding point, or equipment and the rest of the earthing grid.

Possible Causes

Required Tools

Safety Precautions

• LOTO associated equipment before working on the earthing system.
• Confirm an alternative earth path is in place, or equipment is de-energised, before disconnecting or working on the only remaining earth conductor to an item.

Diagnostic Procedure

1. ObservationUse the as-built earthing drawing to trace the conductor's intended route between its two end points.
2. MeasurementTest continuity end-to-end; a break will read as open circuit or very high resistance.
3. ObservationPhysically trace the route (visually where exposed, or by careful excavation where buried, following correct utility-locate procedure) to find the point of separation.
4. DecisionBreak located and accessible → repair or replace the conductor. Break suspected but not located along an accessible route → consider installing a new conductor along an accessible path rather than extended excavation.
5. Fault LocationConfirm the exact point and cause of the break.
6. Root CauseDetermine whether the cause was mechanical damage, fatigue, corrosion, or theft, to inform the repair method and any site security measures needed.

Test Points

Root Cause Verification

After repair, re-test end-to-end continuity and overall earth resistance, and confirm the reading is restored to its expected baseline value.

Corrective Action

• Repair the break using a correctly rated, mechanically sound joint, or replace the full conductor run if the break location is inaccessible or the conductor is otherwise degraded.
• Reinstate any excavation per airport engineering standards.
• Report suspected theft to site security and consider tamper-resistant conductor routing at exposed locations.

Preventive Action

• Include visual inspection of exposed earth conductor runs in the periodic maintenance cycle.
• Route or conceal exposed earth conductor to reduce vulnerability to accidental damage or theft where practical.
• Coordinate with airport works teams to flag earthing conductor routes before any excavation nearby.

Related References

SOP: SOP-ELS-03 (Earth Conductor Fault Location and Repair Procedure), SOP-CCR-04 (CCR LOTO Procedure)

Standards: IS 3043, IEC 60364, ICAO Annex 14 Vol I

Diagram: Earthing/Grounding As-Built Drawing

Case Study: Division 25 — Field Case Study Troubleshooting

Equipment / System

Earth conductor termination point at an electrode, earth bar, equipment earth stud, or test/disconnect link.

Possible Causes

Required Tools

Safety Precautions

• LOTO before working on the connection.
• Treat a loose high-current earth termination as a potential heating/arcing hazard, particularly if it has been carrying fault or surge current.

Diagnostic Procedure

1. ObservationPhysically inspect and attempt to gently move/flex the termination to check for looseness, comparing against a correctly torqued reference connection.
2. MeasurementTest continuity/resistance both in the as-found (loose) condition and after re-torquing, to confirm looseness was the cause of any marginal reading.
3. ObservationCheck for signs of arcing, discolouration, or heat damage at the termination, which would indicate the looseness has already caused electrical stress.
4. DecisionLooseness confirmed as the cause and no thermal damage found → clean and re-torque the connection. Thermal damage or arcing evidence found → replace the termination hardware and inspect the conductor end for damage.
5. Root CauseConfirm whether the looseness is an isolated installation/torque issue or indicative of a broader vibration exposure affecting nearby terminations too.

Test Points

Root Cause Verification

After re-torquing or replacement, re-test continuity/resistance and confirm the reading is stable across repeated gentle flexing of the connection.

Corrective Action

• Clean the termination surfaces and re-torque to the manufacturer's specification.
• Replace termination hardware showing signs of arcing, heat damage, or incorrect original specification.
• Fully reclose and secure any test/disconnect link after testing.

Preventive Action

• Include termination torque-checking in the periodic maintenance cycle, particularly for terminations subject to vibration.
• Use anti-loosening hardware (e.g. spring washers, thread-locking compound where appropriate) at terminations known to be vibration-exposed.
• Document torque values applied at every earthing termination made or remade.

Related References

SOP: SOP-ELS-04 (Earth Termination Inspection and Torque Procedure), SOP-CCR-04 (CCR LOTO Procedure)

Standards: IS 3043, IEC 60364

Diagram: Earthing/Grounding As-Built Drawing

Case Study: Division 25 — Field Case Study Troubleshooting

Equipment / System

Earth electrode, conductor, or termination point, particularly at below-grade or moisture-exposed locations.

Possible Causes

Required Tools

Safety Precautions

• LOTO before disturbing a corroded connection that may be a sole earth path.
• Be aware corroded connections can be structurally weakened — handle with care to avoid unexpected mechanical failure during inspection.

Diagnostic Procedure

1. ObservationVisually inspect the electrode, conductor, and termination for corrosion extent and colour/type, which can indicate the corrosion mechanism (galvanic vs. general).
2. MeasurementTest continuity/resistance across the corroded point and compare against an equivalent uncorroded reference connection elsewhere on the grid.
3. ObservationCheck for dissimilar-metal contact or missing transition hardware at the termination.
4. DecisionCorrosion superficial and resistance within acceptable limits → clean and protect, monitor at next cycle. Corrosion has significantly reduced effective cross-section or resistance is elevated → replace the affected electrode/conductor/termination.
5. Root CauseIdentify the corrosion mechanism — galvanic, soil chemistry, moisture, or stray current — to prevent recurrence at the same or similar locations.

Test Points

Root Cause Verification

After cleaning/protection or replacement, re-test continuity/resistance and confirm the reading is restored to within the acceptable range, and re-inspect at the next scheduled cycle to confirm corrosion has not progressed further.

Corrective Action

• Clean corrosion back to sound metal and apply an appropriate anti-corrosion compound or coating.
• Replace an electrode, conductor, or termination where corrosion has significantly reduced effective cross-section.
• Install correct dissimilar-metal transition hardware where galvanic corrosion is the identified cause.

Preventive Action

• Include visual corrosion inspection of accessible earth connections in the periodic maintenance cycle.
• Use correctly rated, corrosion-resistant materials and transition hardware at every new earthing installation or repair.
• In known aggressive-soil areas, consider corrosion-resistant electrode types or cathodic protection measures at design stage.

Related References

SOP: SOP-ELS-05 (Earth Connection Corrosion Assessment Procedure), SOP-CCR-04 (CCR LOTO Procedure)

Standards: IS 3043, IEEE 80, IEC 60364

Diagram: Earthing/Grounding As-Built Drawing with Soil Data

Case Study: Division 25 — Field Case Study Troubleshooting

Equipment / System

Complete earthing grid — all electrodes, bonding conductors, and interconnections intended to form a single equipotential network.

Possible Causes

Required Tools

Safety Precautions

• LOTO associated equipment before grid continuity testing that involves disconnecting links.
• Ensure at least one confirmed earth path remains connected to critical equipment throughout testing — do not isolate all paths simultaneously.

Diagnostic Procedure

1. ObservationCompare the as-built earthing grid drawing against the actual site, identifying every intended interconnection point and test link.
2. MeasurementTest continuity between every major grid section pairwise, rather than only testing individual electrodes in isolation, to confirm the grid behaves as a single equipotential network.
3. ObservationInspect suspect interconnecting conductors and test links for damage, corrosion, or an open link.
4. DecisionA specific interconnection confirmed open → repair or reinstate that bonding conductor. Grid found to have never been fully interconnected as designed → treat as a design/installation gap requiring a planned remediation.
5. Fault LocationIdentify precisely which interconnection or section is responsible for the discontinuity.
6. Root CauseConfirm whether the discontinuity is a recent fault, longstanding installation gap, or a testing artefact from an open link.

Test Points

Root Cause Verification

After repair, re-test continuity between every grid section and confirm the whole grid behaves as a single low-resistance network, then re-test overall earth resistance.

Corrective Action

• Repair or install the missing/broken interconnecting bonding conductor.
• Reclose any test/disconnect link left open after testing.
• Update the as-built earthing grid drawing to reflect the as-found and as-repaired configuration.

Preventive Action

• Include whole-grid section-to-section continuity testing, not just individual electrode resistance, in the periodic maintenance cycle.
• Require earthing continuity verification as a mandatory commissioning step for any construction or modification work near the grid.
• Maintain a single authoritative, current as-built earthing grid drawing.

Related References

SOP: SOP-ELS-06 (Earth Grid Continuity Test Procedure), SOP-CCR-04 (CCR LOTO Procedure)

Standards: IEEE 80, IS 3043, ICAO Annex 14 Vol I

Diagram: Earthing/Grounding As-Built Drawing

Case Study: Division 25 — Field Case Study Troubleshooting

Equipment / System

Any AGL equipment within the affected circuit(s) or area, plus the associated earthing and surge protection system.

Possible Causes

Required Tools

Safety Precautions

• Do not approach or work on outdoor AGL equipment during active thunderstorm activity — wait until the storm has cleared the area per site lightning safety procedure.
• LOTO all affected circuits before inspection or repair, treating equipment as potentially damaged and unpredictable until assessed.

Diagnostic Procedure

1. ObservationCorrelate the reported fault timing against site weather/lightning strike data to confirm a strike event occurred in the relevant timeframe and area.
2. ObservationConduct a systematic visual inspection of all equipment on the affected circuit(s) for scorching, melted components, cracked housings, or other physical strike damage, not just the first fault found.
3. MeasurementMegger and function-test each item of equipment on the affected circuit(s) individually, since a strike can damage multiple components with varying severity across a wide area.
4. DecisionDamage pattern consistent with a single affected item → isolated repair/replacement. Multiple items affected across the circuit → treat as a wider event requiring full-circuit assessment and review of the surge protection/earthing system's performance.
5. Root CauseConfirm lightning as the cause via physical evidence and weather data, and assess whether the surge protection and earthing system performed as designed or were overwhelmed.

Test Points

Root Cause Verification

After repair/replacement, re-test all affected equipment individually and the full circuit as a whole, and confirm SPDs on the circuit are in a serviceable, indicating-good condition before returning to service.

Corrective Action

• Replace equipment confirmed physically damaged beyond repair.
• Replace any SPDs that operated (sacrificed themselves) in limiting the strike energy, per ELS-418.
• Repair damaged cable sections identified during inspection.
• Document the event, damage extent, and repairs for the site's lightning event history.

Preventive Action

• Review and upgrade surge protection coordination if a strike event reveals inadequate protection for the site's exposure level.
• Maintain a lightning event log correlating strikes with subsequent equipment failures to identify vulnerable circuits.
• Ensure lightning protection system (air terminals, down conductors) inspection is current per its own maintenance schedule.

Related References

SOP: SOP-ELS-07 (Post-Lightning-Event Inspection Procedure), SOP-CCR-04 (CCR LOTO Procedure)

Standards: IEC 62305 (lightning protection), IEEE 80, ICAO Annex 14 Vol I, FAA AC 150/5340-30

Diagram: Lightning Protection and Surge Coordination Drawing

Case Study: Division 24 — Complete Runway Lighting Failure

Equipment / System

Individual SPD unit installed at the CCR panel, distribution point, or field equipment location.

Possible Causes

Required Tools

Safety Precautions

• LOTO before removing or replacing an SPD.
• Treat a failed-short SPD as a potential fault-current path — confirm circuit isolation before handling.
• Follow correct disposal procedure for the failed SPD unit.

Diagnostic Procedure

1. ObservationCheck the SPD's visual status indicator (where fitted) and any associated remote monitoring/alarm status.
2. MeasurementWith the circuit isolated, test the SPD per the manufacturer's procedure to confirm whether it has failed open, failed short, or is a false indication.
3. ObservationReview the site's lightning/surge event history to determine whether the failure correlates with a specific event or appears to be end-of-life degradation.
4. DecisionSPD confirmed failed → replace with a correctly rated unit per manufacturer specification. Indicator found faulty but SPD itself tests serviceable → repair/replace the indicator only.
5. Root CauseDetermine whether the failure was a single significant surge event, cumulative degradation, or an incorrect original rating, to inform whether the replacement SPD should be the same rating or an upgraded one.

Test Points

Root Cause Verification

After replacement, confirm the new SPD's status indicator shows serviceable/good, and verify correct installation (polarity, torque, and connection to the earthing system) before returning the circuit to service.

Corrective Action

• Replace the failed SPD with a unit of the correct rating for the circuit.
• Confirm the SPD's earth connection is sound as part of the replacement, since SPD performance depends on a low-impedance earth path.
• Upgrade the SPD rating if the failure pattern indicates the original specification is inadequate for the site's exposure.

Preventive Action

• Include SPD status verification in the routine maintenance and inspection cycle.
• Stock correctly rated replacement SPDs for rapid restoration after a surge event.
• Log every SPD replacement with date and suspected cause to build a site surge-exposure history.

Related References

SOP: SOP-ELS-08 (SPD Inspection and Replacement Procedure), SOP-CCR-04 (CCR LOTO Procedure)

Standards: IEC 61643 (surge protective devices), IEC 62305, ICAO Annex 14 Vol I

Diagram: Surge Protection Coordination Drawing

Case Study: Division 01 — CCR Troubleshooting (panel-level SPDs)

Equipment / System

SPD location with a documented history of repeated failure, plus the associated circuit, earthing, and surge coordination scheme.

Possible Causes

Required Tools

Safety Precautions

• LOTO before working on the SPD or its earth connection.
• Treat the recurring failure as a signal of a systemic issue rather than simply replacing the SPD again without investigation.

Diagnostic Procedure

1. ObservationReview the failure history for this specific SPD location — dates, replacement frequency, and any correlation with weather events.
2. MeasurementTest the SPD's specific earth connection resistance/continuity independently, since a poor SPD earth is a common cause of repeated failure.
3. ObservationReview the surge coordination drawing to confirm whether an upstream protection stage exists and is itself functioning, and whether this SPD is correctly rated for its position in the coordination scheme.
4. DecisionSPD earth connection confirmed poor → repair the earth connection before replacing the SPD again. Earth connection confirmed good and SPD correctly rated → investigate upstream coordination or consider the site's exposure level for an uprated SPD.
5. Root CauseIdentify the specific systemic cause — poor earthing, incorrect rating, missing coordination stage, or genuine site exposure — rather than treating each failure as an independent event.

Test Points

Root Cause Verification

After addressing the identified systemic cause, monitor the SPD's status over subsequent storm events and confirm it survives events of a severity comparable to those that previously caused failure.

Corrective Action

• Repair the SPD's earth connection if confirmed poor.
• Install or repair a missing/failed upstream surge protection stage to correctly coordinate energy absorption across stages.
• Uprate the SPD specification if the site's actual exposure is confirmed to exceed the original design assumption.

Preventive Action

• Review surge protection coordination design for any location with a repeated-failure history.
• Include SPD-specific earth testing (not just general grid testing) in the maintenance cycle for known repeat-failure locations.
• Consider a lightning risk assessment update if site exposure appears to have changed since original design.

Related References

SOP: SOP-ELS-09 (Repeated SPD Failure Investigation Procedure), SOP-ELS-08 (SPD Inspection and Replacement Procedure)

Standards: IEC 61643, IEC 62305, IEEE 80

Diagram: Surge Protection Coordination Drawing

Case Study: Division 25 — Field Case Study Troubleshooting

Equipment / System

CCR power stage, control/regulation card, and any internal SPD or transient protection fitted within the CCR cabinet.

Possible Causes

Required Tools

Safety Precautions

• LOTO the CCR at its supply and field circuit connections before internal inspection.
• Treat internal CCR components as potentially damaged and holding residual charge — follow manufacturer discharge procedure before handling.

Diagnostic Procedure

1. ObservationRetrieve the CCR's internal fault/event log, where available, to identify the specific failure mode and its timing relative to any known surge event.
2. MeasurementTest the field-circuit-side and mains-side surge protection associated with the CCR independently to determine which path the surge most likely entered through.
3. ObservationInspect the CCR cabinet earthing connection for adequacy, since poor cabinet earthing increases surge stress on internal components.
4. DecisionFailure confirmed surge-related via log/pattern and correlated event → replace the damaged card/component and address the entry path (field or mains side) surge protection. Failure pattern inconsistent with a surge event → investigate as a standard component failure under Division 01.
5. Root CauseDetermine which surge entry path (field circuit or mains supply) was responsible, and confirm the associated protection stage for that path is adequate going forward.

Test Points

Root Cause Verification

After repair, confirm the CCR operates correctly across its full range of outputs/intensity steps, and verify both field-circuit and mains-side surge protection are in a confirmed serviceable state before returning to service.

Corrective Action

• Replace the damaged CCR card/component per manufacturer procedure.
• Replace or install adequate surge protection on the identified entry path (field circuit or mains supply).
• Improve CCR cabinet earthing if found inadequate.

Preventive Action

• Include CCR internal SPD/surge protection status in the routine maintenance cycle.
• Ensure both field-circuit and mains-side surge protection are specified and maintained for every CCR, not just one side.
• Review CCR surge protection coordination after any confirmed surge-induced failure.

Related References

SOP: SOP-ELS-10 (CCR Surge Damage Investigation Procedure), SOP-CCR-04 (CCR LOTO Procedure)

Standards: IEC 61643, FAA AC 150/5345-10, IEC 62305

Diagram: CCR Internal Wiring and Surge Protection Diagram

Case Study: Division 01 — CCR Troubleshooting

Equipment / System

LED fixture driver/power supply module and LED array, plus the isolation transformer and connector serving the fixture.

Possible Causes

Required Tools

Safety Precautions

• LOTO the circuit before opening the fixture.
• Allow the fixture to discharge before handling internal driver components, per manufacturer guidance.

Diagnostic Procedure

1. ObservationCorrelate the fixture failure timing against site weather/lightning strike data to establish whether a surge event is a plausible cause.
2. MeasurementWith the circuit isolated, test the LED driver and LED array independently to identify which component has failed.
3. MeasurementTest the isolation transformer serving the fixture independently to rule in or out surge damage there as well.
4. DecisionDriver confirmed failed and correlates with a surge event → replace the driver and verify the transformer is undamaged before reconnecting. Multiple fixtures on the same circuit affected similarly → treat as a wider circuit-level surge event and inspect all fixtures on that circuit.
5. Root CauseConfirm surge as the cause via correlated timing and driver failure signature, and assess whether the fixture's surge protection/earthing was adequate for the event.

Test Points

Root Cause Verification

After replacement, re-energise the circuit and confirm the fixture operates correctly at all commanded intensity steps, and check neighbouring fixtures on the same circuit for any related but less obvious damage.

Corrective Action

• Replace the failed LED driver or complete fixture as appropriate.
• Replace the isolation transformer if also confirmed damaged by the same event.
• Improve the fixture's earth/bonding connection if found inadequate.

Preventive Action

• Where fixture-level surge protection components are available from the manufacturer, include them in future fixture specifications for surge-exposed circuits.
• Include fixture driver condition checks in post-storm inspection procedures.
• Track LED driver failures by circuit and correlate with weather events to identify surge-vulnerable circuits.

Related References

SOP: SOP-ELS-11 (LED Fixture Surge Damage Investigation Procedure), SOP-CCR-04 (CCR LOTO Procedure)

Standards: IEC 61643, FAA AC 150/5345-46, IEC 62305

Diagram: LED Fixture Internal Wiring Diagram

Case Study: Division 24 — Complete Runway Lighting Failure

Equipment / System

Communication interface cards, data cabling, and any dedicated data-line surge protection at both ends of the affected link.

Possible Causes

Required Tools

Safety Precautions

• LOTO or de-energise per manufacturer procedure before working on communication interface cards.
• Treat data cabling as potentially carrying induced transient voltage following a storm event — do not assume it is safe simply because it is low-voltage under normal conditions.

Diagnostic Procedure

1. ObservationCorrelate the communication failure timing against site weather/lightning strike data.
2. MeasurementTest the communication interface card at each end of the link independently to identify which end (or both) has failed.
3. MeasurementTest the communication cable's insulation and shield/earth continuity, since surge coupling often occurs via an inadequately earthed shield.
4. DecisionInterface card confirmed failed at one or both ends → replace the card(s) and verify/install dedicated data-line surge protection if absent. Cable shield/earth found deficient → correct the shield termination as part of the repair.
5. Root CauseDetermine whether the surge coupled via the data line itself, via the equipment's power/earth system, or via a ground potential difference between the two ends.

Test Points

Root Cause Verification

After repair, confirm the communication link operates correctly with stable, uncorrupted data over an extended monitoring period, and verify data-line surge protection status at both ends.

Corrective Action

• Replace the failed communication interface card(s).
• Install or repair dedicated data-line surge protection at both ends of the link if found absent or failed.
• Correct communication cable shield/earth termination if found deficient.

Preventive Action

• Specify dedicated data-line surge protection for all communication links between separately earthed AGL system components.
• Include communication link integrity checks in post-storm inspection procedures.
• Address any confirmed ground potential difference between communication endpoints per ELS-425.

Related References

SOP: SOP-ELS-12 (Communication Link Surge Damage Investigation Procedure), SOP-CCR-04 (CCR LOTO Procedure)

Standards: IEC 61643, IEC 62305, relevant ALCMS/communication interface manufacturer standards

Diagram: System Communication Architecture Diagram

Case Study: Division 01 — CCR Troubleshooting (remote monitoring interface)

Equipment / System

Series circuit primary cable or communication cable in the vicinity of a known or suspected lightning event.

Possible Causes

Required Tools

Safety Precautions

• LOTO before any cable testing or repair.
• Treat a lightning-damaged cable section as potentially having multiple damage points, not just the first one found.

Diagnostic Procedure

1. ObservationCorrelate the reported cable fault timing against site weather/lightning strike data.
2. MeasurementMegger the cable in segments to bracket the damaged section(s), being alert to the possibility of more than one damage point given the nature of induced transient events.
3. MeasurementUse a TDR or fault locator to estimate the physical location of each damage point within the bracketed section(s).
4. DecisionSingle damage point located and confirmed → repair that section. Multiple damage points suspected from the segment testing pattern → treat as a multi-point fault per SCF-404 and locate each independently.
5. Fault LocationConfirm the specific location(s) and extent of insulation/conductor damage.
6. Root CauseAssess whether the damage pattern indicates a direct strike, an induced transient, or coupling from the earthing grid, to inform whether additional surge protection or cable rerouting should be considered.

Test Points

Root Cause Verification

After repair, re-megger the full cable run and confirm insulation resistance is restored above the acceptable threshold at every previously identified damage point.

Corrective Action

• Repair or replace each identified damaged cable section using correctly rated, sealed splice kits or full replacement as extent of damage requires.
• Reinstate pavement/trench per airport engineering standards at each excavated location.

Preventive Action

• Where a cable route runs in close proximity to the earthing grid or lightning protection down-conductors, review separation distance against IEC 62305 guidance and consider rerouting or additional shielding.
• Include post-storm insulation testing for cable runs in known lightning-exposed areas of the site.
• Maintain a lightning event log correlated with subsequent cable fault reports to identify vulnerable routes.

Related References

SOP: SOP-ELS-13 (Lightning-Induced Cable Fault Investigation Procedure), SOP-SCF-09 (Cable Fault Location and Repair Procedure)

Standards: IEC 62305, IEC 60364, ICAO Annex 14 Vol I

Diagram: Cable Route Drawing with Earthing Grid Overlay

Case Study: Division 25 — Field Case Study Troubleshooting

Equipment / System

CCR earth-fault/ground-fault monitoring circuit and its own reference earth connection, plus the protection setting/threshold configuration.

Possible Causes

Required Tools

Safety Precautions

• LOTO before working on the CCR's monitoring circuit or reference earth.
• Do not simply raise the trip threshold or disable protection to stop nuisance trips without confirming no genuine fault is present.

Diagnostic Procedure

1. ObservationPerform a full insulation resistance test on the field circuit to positively confirm no genuine earth fault is present, rather than assuming this from the trip pattern alone.
2. MeasurementTest the CCR's own reference earth connection resistance and continuity independently of the field circuit's earthing.
3. ObservationReview the CCR's protection threshold setting against the circuit's normal, historically stable leakage current baseline.
4. DecisionField circuit confirmed genuinely fault-free and CCR reference earth confirmed poor → repair the CCR's own earth connection. Field circuit fault-free and CCR reference earth good, but threshold appears overly sensitive → review and adjust the threshold only after engineering approval.
5. Root CauseConfirm whether the nuisance trip originates from the CCR's own earthing, an overly sensitive threshold, or interference, and rule out a genuine minor fault before concluding it is a false alarm.

Test Points

Root Cause Verification

After corrective action, monitor the circuit over subsequent operating cycles at all intensity steps and confirm no further nuisance trips occur, while re-confirming periodically that the circuit remains genuinely fault-free.

Corrective Action

• Repair the CCR's own reference earth connection if confirmed poor.
• Adjust the protection threshold only following engineering review confirming the new setting remains safe and compliant.
• Address identified electromagnetic interference sources where practical.

Preventive Action

• Verify CCR reference earth condition as part of the CCR's own periodic maintenance, separate from field circuit earthing checks.
• Document and review protection threshold settings against actual site baseline data rather than a generic default.
• Log nuisance trip events with full test results to build a clear record before considering any threshold adjustment.

Related References

SOP: SOP-ELS-14 (Earth-Fault Nuisance Trip Investigation Procedure), SOP-CCR-04 (CCR LOTO Procedure)

Standards: FAA AC 150/5345-10, IEC 60364, IS 3043

Diagram: CCR Protection Setting and Reference Earth Diagram

Case Study: Division 01 — CCR Troubleshooting (protection trip investigation)

Equipment / System

Two or more separately earthed points within the AGL system — for example a CCR cabinet and a remote field cabinet, or two buildings/structures with independent earthing systems interconnected by cable.

Possible Causes

Required Tools

Safety Precautions

• Treat any measured ground potential difference as a genuine shock and equipment-damage hazard until characterised and addressed — do not work across the two points without confirming safe potential equalisation.
• LOTO both ends before working on any interconnecting cable or bonding conductor.

Diagnostic Procedure

1. ObservationConfirm and quantify the ground potential difference between the two points, ideally capturing its behaviour during an actual or simulated fault/switching event, since it may not be significant under normal steady-state conditions.
2. MeasurementTest earth resistance at each point independently to identify whether one point has a substantially higher local resistance than the other.
3. ObservationReview the as-built earthing and bonding drawing to confirm whether an equalising bonding conductor is intended to exist between the two points, and if so, test its condition.
4. DecisionA bonding conductor is intended but broken/absent → install or repair it. Bonding conductor present and sound but potential difference persists → investigate soil/grid layout between the points and consider additional electrodes or a dedicated equalising conductor.
5. Root CauseDetermine whether the root cause is a missing/broken bond, an inherent grid layout/soil resistivity issue, or a significant asymmetry in local earth resistance between the two points.

Test Points

Root Cause Verification

After corrective action, re-measure the ground potential difference under representative conditions and confirm it is reduced to within a safe, acceptable margin for the equipment and personnel exposed to it.

Corrective Action

• Install or repair a bonding conductor to equalise potential between the two points where the design intends one.
• Add supplementary earth electrodes at the point with higher local resistance to bring it closer in potential to the other.
• Where full equalisation is impractical, ensure equipment and cabling crossing the interface is rated and protected for the expected potential difference (e.g. isolated interfaces, appropriately rated surge protection).

Preventive Action

• Assess ground potential difference between all separately earthed AGL system interfaces at design stage, not only after a problem is reported.
• Include bonding conductor continuity between critical interconnected points in the periodic earth grid continuity testing (ELS-416).
• Document known ground potential difference risk points on the as-built earthing drawing for future reference.

Related References

SOP: SOP-ELS-15 (Ground Potential Difference Assessment Procedure), SOP-ELS-06 (Earth Grid Continuity Test Procedure)

Standards: IEEE 80, IEC 62305, IS 3043

Diagram: Earthing/Grounding As-Built Drawing with Interconnection Points

Case Study: Division 25 — Field Case Study Troubleshooting