Lightning & Surge Protection for AGL Circuits
Counterpoise, bonding, grounding and surge protection for the complete AGL path from CCR to light and control system, and how to test, maintain and investigate it after a lightning event.
Lightning & Surge Protection for AGL Circuits
Airfield Ground Lighting works over large outdoor areas, often with long underground series circuits, exposed fittings, metallic structures, transformers, connectors and control equipment. That makes the network vulnerable to direct and nearby strikes, induced voltage, earth-potential differences, switching transients, surge propagation along cables and transients on communication and control lines. A fitting can be damaged even when lightning does not hit it directly.
A proper strategy covers the complete AGL electrical path: power supply → CCR → primary circuit → cable → transformer → connector → light, together with grounding and bonding, counterpoise, surge protection and control-system protection.
The aim is not to claim that lightning can be eliminated. It is to control the consequences of lightning and surge energy and keep the required system integrity.
Lightning Protection vs Surge Protection
Lightning protection
Addresses the effects of lightning current and electromagnetic energy.
- Air terminals where required
- Down conductors
- Grounding / earth termination
- Bonding
- Counterpoise
- Equipotentialization
- Physical separation where applicable
Surge protection
Limits transient overvoltage reaching electrical and electronic equipment.
- Surge protective devices (SPDs)
- Surge arresters
- Transient protection
- Protected power supplies
- Signal-line protection
A strong design uses lightning protection + grounding / bonding + surge protection, not only a plug-in SPD. Under FAA AC 150/5340-30J the airfield-lighting lightning-protection system is meant to protect elevated and in-pavement fixtures, NAVAIDs, signs and underground power, communication and control circuits. It is an airfield-wide infrastructure system, not a device in the electrical room.
Where Does the Surge Come From?
Pick an entry path to see what it affects and how it is usually addressed.
A nearby strike induces a surge on the primary cable, which an arrester passes to the earthing bus at the CCR.
AGL Visual Encyclopedia: Lightning surge interface Lightning detector
Protection to consider
Watch points
What Is an AGL Counterpoise?
A bare copper conductor above the primary cable, bonded to ground rods along the route.
AGL Visual Encyclopedia: Bare copper earth conductor Earthing network Earth pit arrangement
A counterpoise is a conductor installed along the airfield lighting system as part of the lightning-protection arrangement. It matters most for long underground circuits. Its location, depth, conductor size and bonding must follow the selected design method and the applicable standard.
Equipotential method
The counterpoise is arranged and bonded so protected field components and the counterpoise rise toward a similar potential during a strike, reducing harmful potential differences and arcing. FAA guidance identifies it for locations with high lightning incidence, subject to engineering selection.
Isolation method
The counterpoise is not bonded to the protected elevated fitting in the same way. FAA guidance limits it to particular elevated-fixture installations on turfed or stabilized shoulders, with specific installation conditions.
FAA AC 150/5340-30J says the two methods should not be mixed on the same circuit. This is also why a counterpoise layout should not simply be copied from another project. Base the method on airfield construction, lightning exposure, pavement, fixture type, soil, cable arrangement and standards.
Protection Zones and the Complete Path
Representative zoning. Each zone has a coordinated protection strategy, and the counterpoise follows the field circuit.
Coordinated SPDs
Protection is usually more effective when coordinated at several interfaces: substation → AGL power room → CCR panel → CCR control → field and control equipment. Coordination depends on the distance between SPDs, response characteristics, protection level, energy capability, conductor impedance and upstream and downstream devices. Use higher-energy protection upstream and finer protection downstream, not identical devices everywhere.
Domains differ
AC power (mains, UPS, DG, CCR input), the series-circuit output (CCR output, field cable, transformers), DC control (CCR controls, field controllers, relays) and communications (Ethernet, fibre, copper, monitoring) can each need a different approach.
Bonding, Grounding and Equipotentialization
With bonding, almost no voltage appears between a fixture body and its base can.
AGL Visual Encyclopedia: Bonding Earthing principle
Bonding leads from a CCR cabinet, a sign housing and a base can to a buried earthing conductor.
AGL Visual Encyclopedia: Equipment earthing Earthing network Earthing installation
Why bonding matters
Lightning can create very large temporary voltage differences. If two metallic parts are not bonded, part A can sit at high potential while part B stays lower, and the result can be arcing, flashover and equipment damage. FAA construction specifications require metallic field components on the CCR output side to be bonded to the lighting counterpoise under the applicable method.
Grounding vs bonding
Grounding / earthing is connection to the earth electrode system. Bonding connects conductive parts to each other to control potential difference. A design may need both, for example light base ↔ bonding conductor ↔ counterpoise, and counterpoise ↔ earth system where the method requires it.
Earth resistance is not the goal
The useful aim is a controlled, coordinated current path and minimal dangerous potential differences, not simply the lowest earth resistance. A low reading alone does not guarantee good lightning performance. Conductor inductance, geometry, current path, parallel paths and connection quality also matter.
Parts to include
Light bases, mounting hardware, fixture bodies, transformer housings, supports, equipment cabinets, cable armour where applicable, the counterpoise and lightning-protection conductors. Design the network so lightning current does not travel through sensitive equipment.
CCR Protection and the Series-Circuit Difference
Protection layers along the CCR power path, from the surge device to the earth monitor.
AGL Visual Encyclopedia: CCR protection Surge protection devices
The CCR is the source of the airfield series circuit and a key item to protect. A strike can affect its input components, power electronics, control boards, communication interfaces, monitoring circuits and output-side insulation. Consider two directions: incoming surge from the supply and field-circuit surge from the cable.
FAA maintenance guidance describes a CCR-fed series circuit as an ungrounded circuit, where earth faults behave differently from an ordinary building circuit. So an SPD suited to a conventional LV board cannot be assumed suitable for the CCR output. Coordinate with CCR topology, output voltage, insulation coordination, series-circuit design, transformer insulation, the surge-current path and the manufacturer’s requirements.
Before selecting an SPD for a CCR, check
- Input voltage and phase configuration
- Earthing system
- Expected transient environment
- Short-circuit capability and upstream protection
- CCR manufacturer requirements
- Control-system interface
- Required protection level
Choosing and Coordinating SPDs
Do not choose by “highest kA available”. Consider
- System voltage and earthing arrangement
- Expected surge environment
- Impulse and nominal discharge current
- Voltage protection level
- Short-circuit capability and follow current
- Coordination with upstream protection
- Equipment withstand level
- Conductor length and installation geometry
Indian standards
BIS lists IS 16463 (Part 11):2016 / IEC 61643-11:2011 for LV SPDs connected to LV power systems, with a 2026 review, and IS 16463 (Part 12):2026 / IEC 61643-12:2020 for selection and application principles. These cover LV power SPDs and do not by themselves settle suitability for the CCR output series circuit.
Lightning Protection by Equipment Type
Surge devices on the mains and control lines of a CCR, each tied to the earthing network.
AGL Visual Encyclopedia: Surge protection devices CCR protection Shielded cable screen connection
Elevated fixtures
More exposed than recessed ones: runway and taxiway edge lights, approach structures, obstruction aids, beacons. Treat fixture → support → base → bonding → counterpoise → earth as one path.
In-pavement fixtures
Exposed to direct or nearby effects, transient current through field conductors, water ingress, insulation stress and surge transfer through transformer and connector. Below pavement is not immunity.
Approach lighting
Can extend beyond the runway environment with elevated and inset fixtures, supports, cables, transformers and control circuits. Review the whole arrangement against project and authority requirements.
PAPI
Optical assemblies, electronics, metal housings, supports, cable connections and transformers. Protect PAPI unit, mounting, circuit, transformer, cable and control interface together. Do not use an arbitrary consumer SPD.
Stop bars
Many inset fittings, transformers, cables and switching interfaces, and a widespread outage affects holding-point protection. Cover power, field circuit, control and monitoring.
Signs
LED modules, drivers, power supplies, control interfaces and metal housings. Bonding, grounding, surge protection and protected communication lines. FAA includes airfield signs in the system scope.
Runway and taxiway circuits
Both can span long distances and affect many visual aids at once, so design the complete circuit rather than each fixture. On a precision runway a strike-related outage can affect many aids simultaneously.
Vaults and electrical rooms
Protect against direct or nearby effects and against transients entering through power and communication networks: building lightning protection, main SPD, bonding, equipment SPDs and signal protection. FAA guidance refers to NFPA 780 for certain structures and vaults in the U.S. context. For India the governing Indian and project requirements apply.
Transformers, Connectors, Cables and LED Fixtures
A cable screen is led out at the gland and bonded to earth, not left floating.
AGL Visual Encyclopedia: Shielded cable screen connection Plug-in isolation transformers Isolation transformer principle
Isolating transformers
The transformer isolates primary from secondary, but that does not make the equipment immune. Transients can couple through capacitance, insulation stress, primary surge, secondary wiring and common bonding structures, so insulation coordination is part of the protection system. FAA keeps a dedicated specification for series-to-series isolation transformers (AC 150/5345-47C).
Connectors
Exposed to moisture, contamination, mechanical stress, transients and ageing. FAA keeps a dedicated connector specification. A poor connection raises local voltage stress and can contribute to insulation failure in a transient.
Underground cables
Burial reduces physical exposure but not transient effects. A long cable is a distributed electrical system: induced voltage → cable → equipment → surge propagation. Consider length, routing, parallel metallic paths, bonding, counterpoise, transformer insulation and equipment withstand. Watch routes beside metallic structures, communication and power cables, fences, pipelines and other grounding conductors, and check induced voltage, coupling, separation and shield termination.
LED AGL
LED fixtures hold arrays, drivers, current control, monitoring and communication electronics. Surges can damage these without visible damage, causing complete failure, reduced output, intermittent operation, driver damage, communication failure or abnormal monitoring status. Coordinated surge protection is particularly valuable.
ALCMS, A-SMGCS, Follow the Greens and Communications
ALCMS
Sensitive electronics with surge-entry paths through AC power, control cables, copper communication, field I/O, remote interfaces and external sensors. Use power SPDs, signal protection, proper earthing and bonding and shield management so an airfield transient does not propagate into the control system.
A-SMGCS and Follow the Greens
Chain: field controller ↔ network ↔ ALCMS ↔ A-SMGCS → green centreline lighting and stop bars. A surge can disturb controller communication, switching, stop-bar control and status monitoring. Include protection in the system-level design, with protected control power, field-controller and network protection, degraded-mode operation and alarms, so the airport never shows an ambiguous or misleading route after a failure.
Copper and fibre
Fibre gives electrical isolation over long optical paths, but equipment on copper interfaces is still exposed. Where copper leaves a protected building, consider surge protection and bonding. Fibre itself carries no lightning current, but metallic armour, messenger wires, shielded cables and termination hardware can, so check the cable construction.
Emergency power
A surge can damage both normal and emergency power equipment. Coordinate protection with UPS, DG, ATS, switchgear and AGL distribution.
Lightning Protection Design in India
Do not copy a foreign airport’s layout. Consider local lightning activity, soil resistivity, airfield geometry, runway and taxiway construction, AGL circuit topology, equipment ratings, authority requirements, electrical standards and project specifications.
BIS lightning standards
BIS identifies the IS/IEC 62305 family covering general principles, risk management, physical damage and life hazard, and protection of electrical and electronic systems within structures. It also lists IS 18925 for lightning-protection components, such as Part 2:2024 for conductors and earth electrodes and Part 6:2025 for lightning-strike counters.
Low-visibility operations
AAI low-visibility procedures monitor AGL serviceability and secondary power availability at airports. That makes lightning resilience part of operational resilience, because a strike-related outage costs more during CAT II/III or other low-visibility operations.
Risk Assessment and Protection Design Workflow
Geographic risk
Lightning density and local climate.
Physical exposure
Elevated structures, open airfield and long exposed infrastructure.
Criticality
Importance of the affected AGL circuit.
Equipment vulnerability
CCR electronics, LED drivers, controllers, communications and ALCMS.
Consequence
Effect on runway operations, low-visibility operations, taxiway movement, ATC and airport availability.
Design workflow
Airport survey
Lightning-risk assessment
System mapping and AGL circuit mapping
Counterpoise and bonding design
Grounding design
SPD coordination and equipment protection
Construction
Inspection
Testing
Commissioning
Periodic maintenance
Typical Lightning and Surge Failure Modes
Click a failure to see the likely path and what to check.
Shorted secondary, open secondary and a surge on the loop, each with its own waveform.
AGL Visual Encyclopedia: Secondary shorting and overvoltage Open secondary core saturation
Where each transformer fault sits, and the symptom it produces.
AGL Visual Encyclopedia: Transformer failure modes CCR failure modes
CCR electronics damaged
Likely path: incoming surge.
- Check input SPD and its status
- Check upstream protection
- Review earthing and bonding
- Compare against manufacturer limits
Multiple lights fail after a storm
Likely path: field-circuit transient.
- Map the failed lights
- Look for clustering on a circuit section
- Check counterpoise continuity
- Check transformers and connectors
Repeated LED driver failure
Likely: inadequate surge protection or bonding.
- Do not just replace the fitting
- Check transformer and secondary leads
- Check bonding at the base
- Review the surge path
Transformer or connector failure
Likely: excessive transient stress, moisture or insulation condition.
- Insulation tests
- Inspect connectors for flashover
- Check for water ingress
- Check coordination
Light-base damage
Likely: lightning current or equipotential issue.
- Inspect bonding and counterpoise
- Check for arcing marks
- Review the chosen method
Control system resets or comms failure
Likely: transient on control power or communication interface.
- Check power SPD
- Check signal-line protection
- Check shield and earthing
- Review cable routing
Stop-bar or PAPI electronics damaged
Likely: power or control-line surge.
- Check power and control protection
- Check the PAPI/stop-bar circuit
- Verify function and photometry after repair
SPD repeatedly fails
Likely: incorrect rating or very high surge exposure.
- Check the rating against the study
- Check installation geometry and earthing
- Review the exposure
After a Lightning Event
Do not only replace what visibly failed. Investigate the pattern: which lights, transformers, controllers or CCRs failed, whether failures cluster in one circuit section, whether SPDs operated, whether counterpoise, bonding and grounding connections are intact, whether several equipment types failed together, and how the transient could have entered. Repeated failure at one location is an important clue.
Troubleshooting a failed LED light
Photometry is not a lightning test, but after a major event it confirms that the lights have returned to the expected optical performance, not only that they turn on. Sequence: electrical testing → equipment inspection → functional testing → photometry.
Testing, Commissioning and Maintenance
Fall-of-potential test of an earth electrode, with the potential probe near sixty-two percent of the distance.
AGL Visual Encyclopedia: Earth resistance testing Earthing inspection
Check the bond lead, the conductor, the clamp and test link, and the rod, in order.
AGL Visual Encyclopedia: Earthing maintenance Earthing inspection Insulation-resistance testing
Test layers
- Visual: counterpoise, bonds, grounding conductors, base connections, SPD condition
- Continuity: intended bonding paths
- Earth / grounding: measured by the approved method
- SPD verification: device, status, connection, coordination
- AGL circuit: insulation, continuity, series-circuit condition, transformer performance
Maintenance
SPDs are not fit-and-forget. Follow manufacturer instructions and the approved maintenance programme.
- Physical inspection and status indicators
- Connection and terminal torque where specified
- Thermal inspection where appropriate
- Replacement after significant surge events when required
- Review SPD alarm contacts
- Counterpoise, bonding and grounding inspection
Commissioning
Design review
Lightning and surge-protection philosophy.
Material inspection
Counterpoise conductor, bonding components, earth electrodes, SPDs, accessories.
Installation inspection
Verify physical installation.
Bonding test
Verify intended connections.
Earthing test
Verify the grounding system.
SPD inspection
Correct type, location and status.
AGL electrical test
Field-circuit insulation and continuity.
Functional test
Operate the lighting system.
Control-system test
ALCMS and field-controller behaviour.
Documentation
Record results as the initial protection baseline.
Counterpoise inspection
Verify continuity where testable, bonding connections, mechanical damage, corrosion, accidental disconnection and construction damage. Take particular care after runway rehabilitation, taxiway construction, trenching, utility installation, drainage work and foundation changes. Civil works can silently disconnect the network.
SPD inspection
Check the status indicator, alarm contact, enclosure, wiring, upstream protective device, signs of thermal damage and replacement status. A failed SPD can stay installed while giving little or no protection.
New Airports, Existing Airports and Gap Assessment
New airports
Build lightning protection into the initial AGL design to avoid expensive retrofit.
- AGL and primary-cable layout
- Counterpoise layout and light-base bonding
- Transformer, CCR and control-system protection
- Earthing network
- Approach, PAPI, sign and communication protection
Existing airports
Start with inspection and a gap assessment, then a prioritized rehabilitation plan.
- Existing counterpoise, earthing and bonds
- Existing CCR, SPD and control protection
- Lightning failure history
- Repeated equipment failures
| Area | Condition | Risk | Recommended action |
|---|---|---|---|
| Counterpoise | Damaged or unknown | High | Survey and repair |
| Light bonding | Inconsistent | High | Standardize |
| CCR input SPD | Missing or failed | High | Review and install |
| ALCMS power | Protected | Low | Maintain |
| Communication | Unprotected | Medium | Evaluate SPD |
| Earth connection | Poor documentation | Medium | Test and document |
| Transformer | Repeated failures | High | Investigate the surge path |
Service scope
Common Mistakes in AGL Lightning Protection
Installing only an SPD
An SPD does not replace counterpoise, bonding, grounding or proper cable design.
Using building practice without AGL analysis
An AGL series circuit behaves differently from building distribution.
Ignoring the CCR output circuit
The series circuit needs protection that suits its actual architecture.
Mixing counterpoise methods
FAA guidance says not to mix equipotential and isolation methods on one circuit.
Poor bonding
No SPD compensates for missing or high-impedance bonds.
Forgetting communication interfaces
ALCMS and A-SMGCS interfaces are exposed to transients too.
No post-lightning inspection
Replacing failed fittings without finding the surge path leads to repeat failures.
Standards and References
FAA (U.S.-specific)
AC 150/5340-30J, Design and Installation Details for Airport Visual Aids, gives detailed guidance on counterpoise, bonding, grounding and lightning protection. FAA’s current list shows it alongside AC 150/5340-26C for maintenance. Neither is an Indian or ICAO requirement.
Indian baseline (project by project)
Build the compliance matrix around the contract and authority requirements.
- IS/IEC 62305 series
- IS 16463 (Part 11) and (Part 12), corresponding to IEC 61643
- IS 18925 series for LPS components
- DGCA, AAI, contract and manufacturer requirements
AGL Lightning Protection Design Checklist
Click an item to mark it complete.
Risk, counterpoise and earthing
Bonding and surge protection
Field equipment and documents
Quick Knowledge Check
Q1. What does a counterpoise do in an AGL installation?
Q2. Can the equipotential and isolation methods be mixed on one circuit?
Q3. Can any standard LV SPD be fitted on a CCR output?
Q4. The same runway lights fail after every storm. What should you do?
Q5. After runway rehabilitation, what should be checked?
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Existing guide on surge and lightning mitigation.
Open AGL Surge Protection & Lightning Mitigation →Emergency Power & Lighting Systems
UPS, DG and switch-over performance.
Open Emergency Power & Lighting Systems →CCR Working Principle
Constant current regulators and series circuits.
Open CCR Working Principle →Airport Isolating Transformer
The transformer between circuit and light.
Open Airport Isolating Transformer →PAPI Engineering Guide
Precision approach path indicators.
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Test and commission AGL systems.
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Maintenance cycles and checks.
Open AGL Preventive Maintenance Guide →How Airfield Lighting Works
The full AGL system explained.
Open How Airfield Lighting Works →ICAO Aerodrome Lighting Requirements
Framework and requirements.
Open ICAO Aerodrome Lighting Requirements →AGL Photometry India
In-field photometric testing for Indian airports.
Open AGL Photometry India →Airport Lighting Companies India
Company types across the Indian AGL market.
Open Airport Lighting Companies India →Protect the Whole Path.
From counterpoise and bonding to SPD coordination, testing and maintenance, explore the complete AGL knowledge base.
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Lightning & Surge Protection FAQ
Q1Why does an AGL circuit need lightning protection?
AGL circuits cover large outdoor areas and include long cables, transformers, connectors, light fittings and electronic controls. Lightning can create direct or induced transients that damage these components.
Q2What is a counterpoise in airport lighting?
A conductor installed as part of an AGL lightning-protection arrangement to help control lightning-related potential differences and provide a designed bonding and current path.
Q3Is a counterpoise the same as an earth wire?
No. A counterpoise, a grounding network and bonding conductors can perform different functions depending on the protection design.
Q4Does every AGL circuit use the same counterpoise arrangement?
No. It depends on the selected method, installation type, airfield construction, local conditions and governing requirements. FAA guidance, for example, distinguishes equipotential and isolation methods.
Q5Can a standard electrical SPD be installed on an AGL CCR output?
Not automatically. A CCR-fed series circuit differs from a conventional LV distribution circuit, so the device and installation must suit the actual circuit and equipment. FAA maintenance guidance describes the CCR-fed field circuit as ungrounded.
Q6Where should SPDs be installed?
It depends on the system design and protection study. Typical points include incoming power, distribution boards, control power, sensitive electronic equipment and communication interfaces.
Q7Can lightning damage LED runway lights?
Yes. LED fittings contain drivers and control electronics that transient overvoltage can damage even when the fitting looks normal.
Q8Why do the same runway lights keep failing after storms?
Repeated failure in one place can point to an unresolved surge path, inadequate bonding, a damaged counterpoise, transformer stress, connector problems or poorly coordinated surge protection.
Q9Does lightning protection eliminate lightning damage?
No. The aim is to reduce risk, control current paths and limit transient stress to acceptable levels.
Q10Does PAPI need lightning protection?
Include PAPI in the airport’s lightning and surge-protection assessment, considering its electrical circuit, transformer, mounting and control arrangements.
Q11Does ALCMS need surge protection?
Yes, where its power and external interfaces are exposed to transients, the protection strategy should include the control and communication architecture.
Q12How often should AGL lightning protection be inspected?
The interval comes from the airport’s approved maintenance programme, applicable standards and equipment requirements. Inspect especially after major lightning events and after civil works that may have disturbed counterpoise or bonding.
Q13Can lightning protection be added to an existing airport?
Yes. Do a gap assessment, then upgrade counterpoise, bonding, grounding, SPDs and control-system protection as required.
Engineering & Expert Notes
Surge Protection and Lightning Protection Are Different Jobs
ConceptsBe clear which one you are designing or inspecting. Each addresses different threats.
Keep Bonding Leads Short
BondingLong or looped leads reduce effectiveness. Check routing during installation and inspection.
Coordinate Devices Across the System
CoordinationVerify ratings and sequence for devices at the CCR, along the circuit and at control equipment.
Inspect After Storms
InspectionCheck device status and look for damage after lightning events.
Do Not Forget Communication and Control Lines
ControlData and signal cables can carry surges into sensitive equipment.
Record Earthing Measurements
RecordsKeep test results to track changes in earth resistance.
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Please read before relying on any content on this page or on any record downloaded from it.
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