Home/ Knowledge Hub/ CCR Working Principle
Safety-critical technical reference — read before use. Independent educational guidance for qualified AGL and aerodrome personnel. It is not an approved procedure, design, specification or regulatory instruction and does not replace your aerodrome’s permit-to-work, isolation/LOTO procedures, the approved design or the manufacturer’s instructions. Series-circuit AGL equipment can carry lethal voltages. Read the full disclaimer ↓
THE AGL ENGINEERING CENTRE by Precision AGL Academy · Electrical Systems

CCR Working Principle in Airport Lighting

How a Constant Current Regulator controls the series circuit — current steps, wiring, remote control, fault indications, troubleshooting, efficiency and commissioning.

Start Learning Jump to Troubleshooting
Overview

What Is a CCR?

A Constant Current Regulator supplies and controls the current in a series-circuit AGL system.

A Constant Current Regulator (CCR) regulates the series-circuit current to a selected operating value, unlike a conventional supply that mainly maintains a fixed voltage. This allows many fixtures to share one series circuit while giving selectable lighting intensity.

The CCR is not simply a power source. It is part of a complete system: series circuit, cables, isolation transformers, connectors, fixtures, control system and monitoring system.

Airport Supply
CCR
Primary Cable
Primary Connector
Isolation Transformer
Secondary Connector
AGL Fixture

The output voltage is not necessarily constant — it changes with the electrical characteristics and total load of the connected series circuit. That is the fundamental principle of CCR operation.

CCR System Overview

CCR SYSTEM OVERVIEW BLOCK VIEW · ONE CCR FEEDING ONE SERIES CIRCUIT SUPPLY Input power BREAKER Input protection REGULATOR Holds the set current OUTPUT To the series circuit CONTROL BOARD Sets brightness step MONITORS Voltage, current, temperature LOCAL / REMOTE Operator and ALCMS
Figure 1. CCR System Overview block diagram.
AGL Visual Encyclopedia: CCR System Overview CCR Power Input CCR Failure Modes
Purpose

Why Is a CCR Used in Airport Lighting?

Runways, taxiways and approach systems have many fixtures spread over a large area.

Controlled light intensity

Different CCR current steps give different lighting intensity levels.

Long-distance distribution

One series circuit supplies numerous fixtures around the airfield through individual isolation transformers.

Controlled operation

Operate from local controls or integrate into an airport lighting control system.

Monitoring

Monitored CCRs detect selected abnormal conditions in the regulator or series circuit.

System integration

The CCR forms part of the larger airport electrical and lighting-control architecture.

Constant-Current Circuit

SERIES LOOP · CONSTANT CURRENT CURRENT FIXED · VOLTAGE ADJUSTS CCR I = SET OUT RTN I SENSE T1 SAME I T2 SAME I T3 SAME I T4 SAME I 1 THE CCR SENSES THE LOOP CURRENT 2 IT ADJUSTS ITS OUTPUT VOLTAGE TO HOLD IT 3 EVERY LAMP GETS THE SAME CURRENT LOAD CHANGES VOLTAGE ADJUSTS CURRENT HOLDS AT THE SET VALUE BRIGHTNESS STEP CURRENT SETS BRIGHTNESS HIGHER STEP = HIGHER CURRENT OUTSIDE THE RATING REGULATION IS LOST OVERLOAD OR OPEN LOOP SCHEMATIC · LOOP SHORTENED · NOT TO SCALE
Figure 2. Diagram of a constant-current circuit on an airfield series lighting loop: the CCR senses the loop current, adjusts its output voltage to hold it at the set value, and every lamp receives the same current.
AGL Visual Encyclopedia: Constant-Current Circuit CCR Current Control Earth Fault
Core Concept

CCR Working Principle

Remember one principle: the CCR regulates current, while the connected series circuit determines the voltage needed to maintain it.

Current = controlled

The CCR holds the selected series current (for example 6.6 A).

Voltage = load-dependent

Higher circuit impedance needs higher output voltage; lower impedance needs less.

V = I × Z

V is circuit voltage, I is series current, Z is circuit impedance.

Try it: V = I × Z at a fixed 6.6 A

Drag the slider to change total series-circuit impedance. The CCR holds current; the required output voltage follows the load.

Illustrative figures only, to show the relationship. Real values come from the approved circuit design and CCR datasheet.

Common misunderstanding: "A 6.6 A CCR should always produce the same output voltage." That is not correct. Always evaluate CCR output voltage together with current and circuit condition.

CCR Current Control

CCR CURRENT CONTROL LOOP · HOW THE CURRENT IS HELD CONSTANTSETPOINTfrom stepCONTROLLERcomparePOWER STAGEadjustOUTPUTTRANSFORMERΣ+−CTTO CIRCUITFEEDBACK · MEASURED OUTPUT CURRENTSUPPLY & LOAD CHANGESPROTECTION: OVERCURRENT · OPEN-CIRCUIT · OVER-TEMPERATURE1SETPOINTtarget current from the selected step2CURRENT SENSINGoutput current measured continuously3CONTROLLERcompares measured with target, corrects4POWER STAGEadjusts power delivered to the output5DISTURBANCESsupply and load changes corrected6LIMITS & PROTECTIONovercurrent and open-circuit protection1 · Setpoint2 · Current sensing3 · Controller4 · Power stage5 · Disturbances6 · Limits & protection
Figure 3. Feedback loop of a constant current regulator: a setpoint from the selected step is compared with measured output current, the controller adjusts the power stage, the output transformer feeds the series circuit, and a current transformer sends the measured current back, with six numbered items: setpoint, current sensing, controller, power stage, disturbances, and limits and protection.
AGL Visual Encyclopedia: CCR Current Control CCR Thyristor Constant-Current Circuit CCR Output Measurement
Circuit

CCR and the AGL Series Circuit

The same controlled current flows through the whole loop.

CCR
Primary Cable
Transformer 1
Fixture 1
Transformer 2
Fixture 2
Return to CCR

The primary of each isolation transformer is connected into the series circuit; the secondary feeds its fixture. The high-voltage series circuit and each fixture are therefore electrically separated. The primary-circuit "loads" are mainly the transformer inputs and associated components — the lamps or LEDs sit on transformer secondaries, an important distinction when troubleshooting.

Role of the isolation transformerDetail
IsolationSeparates the primary series circuit from the individual fixture
ConversionConverts series-circuit conditions into the appropriate secondary supply for the fixture
QuantityEvery lighting point may have its own transformer, all on the same series circuit
Simplified concept only. Actual wiring must follow the approved electrical design, manufacturer drawings and project specifications.

CCR-to-Series-Circuit Interface

CCR · SERIES CIRCUIT INTERFACE WHERE THE CCR MEETS THE LOOP CCR CONSTANT CURRENT THE INTERFACE TERM TERM OUT RTN ISOLATING SWITCH CABLE TERMINATION PRIMARY CABLE TO THE LOOP TRANSFORMERS + FIXTURES 1 THE OUT AND RTN TERMINALS START THE LOOP 2 THE ISOLATING SWITCH DISCONNECTS THE CIRCUIT FROM THE CCR 3 THE CABLE TERMINATION CONNECTS THE PRIMARY CABLE MUST MATCH CCR RATING = CIRCUIT LOAD CURRENT, POWER AND VOLTAGE INSULATION CABLE RATED FOR THE OUTPUT MAXIMUM CCR OUTPUT VOLTAGE HAZARD NEVER OPEN A LIVE LOOP ISOLATE THE CCR FIRST SCHEMATIC · GENERIC · ARRANGEMENTS VARY BY INSTALLATION
Figure 4. Diagram of the CCR-to-series-circuit interface: the CCR OUT and RTN output terminals, an isolating switch and the primary cable terminations form the interface, after which the primary cable runs to the loop.
AGL Visual Encyclopedia: CCR-to-Series-Circuit Interface CCR Transformer CCR Location
Input & Output

CCR Input and Output

Two major electrical sides.

CCR Input

Connects to the airport distribution system. May include incoming feeder, circuit protection, main switching, surge protection, control power, grounding and bonding, and input monitoring.

CCR Output

Connects to the series circuit: output terminals, series cables, primary connectors, isolation transformers, secondary connectors and fixtures. Output voltage can be substantial on a long circuit — treat it as a high-energy system.

CCR Output Measurement

CCR · OUTPUT MEASUREMENT THE CCR MEASURES ITS OWN OUTPUT CCR CONTROLLER POWER STAGE THYRISTORS + TRANSFORMER FIRING DISPLAY A · V · kW OUTPUT CURRENT SENSOR MEASURED CURRENT OUT RTN TO THE LOOP TRANSFORMERS + FIXTURES 1 THE SENSOR ON THE OUTPUT MEASURES THE LOOP CURRENT 2 THE CONTROLLER COMPARES IT WITH THE TARGET FOR THE BRIGHTNESS STEP 3 THE POWER STAGE IS ADJUSTED UNTIL THE TWO MATCH 4 THE DISPLAY SHOWS OUTPUT CURRENT, VOLTAGE AND POWER NEVER OPEN A LIVE LOOP TO INSERT A METER
Figure 5. Diagram of CCR output measurement: the power stage feeds the OUT and RTN terminals through an output current sensor.
AGL Visual Encyclopedia: CCR Output Measurement CCR Power Input CCR Power Output
Current Steps

CCR Current Setting & Brightness Control

Brightness steps are predefined current settings.

Step (FAA Class 1, typical five-step)Nominal current
Step 12.8 A
Step 23.4 A
Step 34.1 A
Step 45.2 A
Step 56.6 A
Other configurations and projects use different current steps. Check the CCR nameplate, approved datasheet and project specification before applying any value in the field.

Lower current gives lower light output and selected intensity; higher current gives higher. The exact relationship depends on the fixture — an LED fixture does not necessarily behave like an incandescent one — so the CCR and lighting load must be treated as a compatible system.

CCR Step Brightness ReferenceCCR Capacity Calculator

CCR Intensity Steps

CCR OUTPUT CURRENT BY STEP · WHAT INTENSITY STEPS ARETYPICAL 5-STEP CCR · OUTPUT CURRENT PER STEP2.8 ASTEP 13.4 ASTEP 24.1 ASTEP 35.2 ASTEP 46.6 ASTEP 5MAX RATED CURRENT3-STEP CCR (TYPICAL): 4.8 A · 5.5 A · 6.6 A1DISCRETE STEPSa small set of fixed brightness settings2RATED CURRENT PER STEPeach step has its own output current3CURRENT SETS BRIGHTNESSlight output is not proportional to current4STEP SELECTIONtower, control system or local panel5TOLERANCE & CHECKSmeasured current compared with rated6OPERATIONAL USEmatched to daylight, dusk, night, low visibility1 · Discrete steps2 · Rated current per step3 · Current sets brightness4 · Step selection5 · Tolerance & checks6 · Operational use
Figure 6. Bar chart of a typical five-step constant current regulator showing rising output current from step 1 to step 5, with a three-step comparison, and six numbered items: discrete steps, rated current per step, current sets brightness, step selection, tolerance and checks, and operational use.
AGL Visual Encyclopedia: CCR Intensity Steps CCR Step Selection CCR Current Control
Control Loop

How Does a CCR Control Current?

A feedback-based closed loop compensates for changing circuit conditions.

Measure current
Compare with setpoint
Correct regulator output
Maintain series current

The full closed loop

Current sensor
Measured current
Control system
Power regulation
CCR output
Series circuit

Internal technology varies by manufacturer and may combine power semiconductors, transformers, reactors, control electronics, current sensors, feedback and protection circuits and digital controllers. Obtain exact construction from the manufacturer's documentation. If measured current falls below the selected value the regulator corrects its output; if it rises above, the regulator limits or reduces output.

Thyristor CCRIGBT CCRFerroresonant CCRThyristor vs IGBT

Different CCR Technologies

FOUR CCR TECHNOLOGIES · SAME CURRENT, DIFFERENT METHODS THYRISTOR (SCR) phase-angle control FIRE PHASE-ANGLE FIRING fires later for lower current closed loop on output current chopped waveform: true-RMS meter SATURABLE REACTOR magnetic control DC CONTROL DC SETS THE OUTPUT control current sets the output no switching of the supply older design, still in service MOVING COIL constant-current transformer FIXED MOVES COIL POSITION SETS CURRENT secondary coil moves mechanical parts to inspect output close to supply waveform SWITCH-MODE high-frequency switching FILTER PULSE WIDTH SETS OUTPUT pulses filtered to the output newer solid-state design follow the maker's data
Figure 7. Four CCR technologies in schematic: thyristor phase-angle control shown as a chopped waveform, a saturable reactor with a DC control winding, a moving-coil constant-current transformer with a fixed primary and a moving secondary, and a switch-mode regulator shown as a pulse train into a filter.
AGL Visual Encyclopedia: Different CCR Technologies CCR Thyristor Ferroresonant CCR IGBT CCR Smart CCR
Control

CCR Remote & Local Control

Control architecture differs from airport to airport.

ATC / Airport Operations
ALCMS
CCR Control Panel
CCR
AGL Series Circuit

Local mode

The operator controls the regulator directly from the cabinet.

Remote mode

Commands arrive from an external system.

  • CCR ON / OFF
  • Brightness steps 1–5
  • Status
  • Fault indication

This architecture lets airport personnel control lighting intensity and monitor system status from a central location. A single CCR circuit then feeds one group of lights — runway, taxiway or approach — and each circuit can have its own rating, current, control method and monitoring requirements.

Remote vs Local ControlALCMS

CCR Remote Control

OPERATING A CCR FROM A DISTANCE · WHAT REMOTE CONTROL INVOLVESTOWER PANELair traffic controlWORKSTATIONlighting staffALCMS& linkCMDFEEDBACKCCRLOCAL / REMOTELOCALREMOTESTEP · CURRENTLOCAL PANELat the CCRTO SERIES CIRCUIT1CONTROL POSITIONtower panel, control-room workstation2COMMAND PATHthrough the control system and link3LOCAL / REMOTE SELECTORdecides which source is in charge4PRIORITY & INTERLOCKSauthority and conflicting commands blocked5CONFIRMATION FEEDBACKactual state, step and current returned6REMOTE FAILUREalarm, configured fallback, local control1 · Control position2 · Command path3 · Local / remote selector4 · Priority & interlocks5 · Confirmation feedback6 · Remote failure
Figure 8. Tower panel and control-room workstation sending commands through the airfield lighting control system to a constant current regulator with a local and remote selector, a local panel as alternative control, and confirmation feedback returning, with six numbered items: control position, command path, local and remote selector, priority and interlocks, confirmation feedback, and remote failure.
AGL Visual Encyclopedia: CCR Remote Control CCR Local Control CCR Control Architecture ALCMS-to-CCR
Wiring

CCR Wiring

Divide wiring into functional groups; take terminals from the manufacturer's approved wiring diagram.

16.1 Input power

Incoming phase, neutral where applicable, earth/ground, main protection, switching, surge protection.

16.2 Series output

CCR output → primary cable → primary connector → isolation transformer → series circuit continues.

16.3 Remote control

ON/OFF, brightness commands, local/remote selection, control returns, interface relays.

16.4 Monitoring

CCR status, output status, fault, series-circuit condition, alarm, remote indication.

16.5 Grounding & protection

Protective grounding, bonding, surge, circuit, cabinet and control-line protection.

FAA Designations

L-828, L-829 and L-827

Commonly met on FAA-based projects; not the manufacturer's model number.

L-828

Constant current regulator without monitoring.

L-829

Constant current regulator with monitoring.

L-827

Regulator monitor.

Monitored CCR (L-829)Regulator Monitor (L-827)Monitoring vs Non-Monitoring
Monitoring & Faults

CCR Monitoring and Fault Codes

Monitoring adds a layer of awareness where faults affect operational availability.

Depending on equipment and specification, monitored conditions may include input power loss, regulator protective shutdown, significant series-circuit load loss, failure to maintain selected current and selected lamp-load failure conditions.

There is no universal CCR fault-code language: one manufacturer's F01 may mean something entirely different from another's. Always use the manufacturer's fault-code table.

Input power failureOver-currentOpen circuitOver-voltageUnder-currentRegulator protectionThermal faultControl faultCommunication faultSeries-circuit faultMonitoring fault

CCR Fault Indication

CCR FAULT INDICATION FROM INDICATION TO FIRST CHECK SYMPTOM What is seen INDICATION Lamp, code, relay FIRST CHECK Supply, output, circuit CAUSE Located and fixed NO OUTPUT Check supply and trips OPEN CIRCUIT Break in the loop EARTH FAULT Insulation breakdown
Figure 9. CCR Fault Indication block diagram.
AGL Visual Encyclopedia: CCR Fault Indication CCR Alarm System CCR Failure Modes
Faults

CCR Fault Conditions

Tap a card for possible causes.

Open-circuit fault

Possible causes

  • Broken primary cable
  • Disconnected connector
  • Failed isolation transformer / open winding
  • Incorrect termination
  • Damaged cable joint
  • Open switching device
  • Disconnected fixture circuit

Short-circuit / over-current

Possible causes

  • Wiring fault
  • Incorrect connection
  • Damaged equipment
  • Circuit fault
  • Internal CCR malfunction
  • Switching abnormality

Low output current

Possible causes

  • Control setting
  • Input supply
  • Current sensing
  • Regulation system
  • Protection status
  • Output circuit / series-circuit load

High output voltage

Possible causes

  • Open or partially open series circuit
  • Disconnected transformer
  • Failed component / missing load
  • Incorrect circuit configuration
  • High circuit impedance
  • CCR control problem

An open circuit leaves no complete current path, so the CCR may be unable to maintain the selected current; its protection and monitoring may detect it. Never bypass CCR protection during troubleshooting. A low-current problem is not automatically a cable fault — investigate both the regulator and the whole circuit. A high voltage by itself does not mean the CCR is defective: always compare output voltage with output current.

Open-Circuit Protection (OCP)

SERIES CIRCUIT · A BREAK IN THE LOOP AND THE CCR’S OPEN-CIRCUIT PROTECTION CCR OUTPUT CURRENT SENSE OCP LOGIC OUTPUT CONTACTOR OUTPUT SHUT DOWN ON TRIP BREAK · OPEN ENDS HIGH VOLTAGE IF ENERGISED ISOLATION TRANSFORMERS · LAMPS OUT EVERY LAMP ON THE CIRCUIT GOES OUT ALARM · CONTROL SYSTEM / TOWER OUTPUT VOLTAGE AFTER THE BREAK WITHOUT OCP · CLIMBS TOWARD THE CCR MAXIMUM WITH OCP · TRIPS, OUTPUT OFF TIME → 1 · BREAKNo current path, all lamps out 2 · SENSECCR sees no current and rising volts 3 · TRIPOutput off, fault latched, alarm raised OCP LIMITS THE VOLTAGE AND THE DAMAGE · THE BREAK STILL HAS TO BE FOUND AND REPAIRED
Figure 10. Diagram of a constant current regulator driving a series loop of cable with four isolation transformers whose lamps are all dark.
AGL Visual Encyclopedia: Open-Circuit Protection (OCP) CCR Protection Earth Fault
Performance

CCR Efficiency, Power Factor & Losses

Related but different.

Efficiency

Efficiency (%) = Output Power ÷ Input Power × 100. Example: 9.2 kW out for 10 kW in = 92%. Depends on design, loading, current step, input conditions, power factor, temperature and manufacturer technology.

Power factor

Relates real power to apparent power. A CCR can have good efficiency yet a different power-factor characteristic; review both.

Heating & losses

Heat, switching, transformer, semiconductor, control and magnetic losses. CCR rooms and vaults need suitable thermal conditions; excess temperature shortens life and can cause abnormal operation.

Evaluate against the applicable equipment specification and manufacturer's published data.

CCR output waveform distortion

CCR OUTPUT WAVEFORM DISTORTION · THE CURRENT INTO THE SERIES CIRCUIT the shape of the output depends on the CCR type, and it decides which meter can be trusted 1 OUTPUT WAVE BY CCR TYPE THYRISTOR · CHOPPED FERRORESONANT · FLAT-TOPPED IGBT · FILTERED TOWARDS A SINE THE SHAPE VARIES BY CCR TYPE drawn as sketches, not measured waves 2 WHAT THE METER READS TRUE CURRENT TRUE-RMS METER READS LOW AVERAGE READING ILLUSTRATIVE AVERAGE METERS CAN READ WRONG here on a chopped wave, calibrated for a sine 3 WHY IT MATTERS LAMPS FOLLOW THE RMS CURRENT effective value sets the output TRANSFORMERS CAN RUN HOTTER harmonics add core and winding loss WRONG READING, WRONG STEP the output looks right, and is not IT CHANGES WHAT YOU MEASURE and what the circuit has to carry WHERE THE OUTPUT WAVEFORM GOES CCR OUTPUT chopped or filtered wave SERIES CIRCUIT partly smoothed by inductance LAMP CURRENT effective (RMS) value counts TRUE-RMS CHECK at the approved test point TRUE-RMS INSTRUMENT READ WITH THE RIGHT METER Step current checked at the approved test point under the permit AVERAGE-READING METER A WRONG NUMBER ON A GOOD CCR Reads wrong on a chopped wave; the CCR may be adjusted wrongly SCHEMATIC · ILLUSTRATIVE SHAPES · NOT TO SCALE · FOLLOW THE CCR MANUAL AND THE SITE PERMIT
Figure 11. Simplified view of CCR output waveform distortion.
AGL Visual Encyclopedia: CCR output waveform distortion Harmonics and power factor on CCR input CCR Cooling System
Design

CCR Sizing and Selection

Size from the whole series-circuit design, not just "number of lights × fixture wattage".

Review areaWhat to check
Electrical supplyInput voltage, frequency, phase, available capacity
Series circuitCircuit length, fixture and transformer quantity, cable characteristics, maximum circuit voltage
Lighting loadFixture type and rating, lamp or LED technology, power factor, VA characteristics
Operational requirementsBrightness steps, minimum and maximum intensity, local control, remote control, monitoring
ProtectionOpen-circuit, over-current, surge and thermal protection
Future requirementsAdditional fixtures, expansion, LED retrofit, control-system integration

Consider fixtures + transformers + cable + connectors + CCR as one system. CCR sizing should be supported by an engineering calculation and the manufacturer's recommended application range. A single airport has separate CCR circuits for runway edge, centreline, threshold, taxiway, stop bars, approach, PAPI and other aids, each with its own rating, current, control and monitoring needs.

CCR CapacitySeries Circuit LoadSeries Circuit ImpedanceTransformer VA Selection

CCR loading limits and minimum-load issues

CCR LOADING LIMITS · WORKING BETWEEN A MINIMUM AND A MAXIMUM too heavy and it cannot hold the current, too light and it regulates and runs poorly 1 THE LOADING RANGE MINIMUM RATING LIGHT DESIGN RANGE OVER THIS CIRCUIT LAMPS FAIL FIXTURES ADDED THE LOAD DRIFTS OVER TIME zone edges are illustrative, not limits 2 TOO LIGHT LOWER POWER FACTOR less of the input kVA does work LESS ACCURATE REGULATION depends on the CCR design LOWER EFFICIENCY a large CCR on a small load BELOW THE MINIMUM LOADING check the manufacturer's data 3 TOO HEAVY CANNOT HOLD THE CURRENT high steps fall short, lamps dim OVERHEATING over rating, life shortens PROTECTION TRIPS overload or overvoltage cut-out PAST THE RATING no spare capacity left WHAT MAKES UP THE CIRCUIT LOAD LAMPS fixture power + TRANSFORMER LOSSES isolation transformers + CABLE I²R heat in the series cable = CIRCUIT LOAD checked at the top step BETWEEN MINIMUM AND RATING SIZED WITH MARGIN, TESTED LIGHT Checked at the highest step and again with lamps out OUTSIDE THE RANGE DIM LAMPS OR POOR REGULATION Overload dims lamps or trips; very light load can regulate poorly SCHEMATIC · ILLUSTRATIVE ZONES · NOT TO SCALE · LIMITS COME FROM THE CCR DATA SHEET AND THE STANDARD
Figure 12. Simplified view of CCR loading limits.
AGL Visual Encyclopedia: CCR loading limits and minimum-load issues CCR Selection Circuit Load
LED

CCR and LED Lighting

LED fixtures have changed the electrical behaviour of AGL circuits.

LED systems contain electronic power supplies that can introduce different power factor, VA characteristics, current waveform, harmonic behaviour, startup characteristics and dynamic loading. An LED retrofit should include a compatibility review of LED fixture + isolation transformer + series circuit + CCR — especially when replacing many traditional fixtures on an existing circuit.

LED Retrofit ProjectsLED AGL

LED Power-Draw and CCR Re-sizing After Retrofit

SAME 60-FIXTURE CIRCUIT · LOAD BEFORE AND AFTER THE RETROFIT · ILLUSTRATIVE 0 2.5 kW 5 kW 7.5 kW 1 · HALOGEN (BEFORE) 7.5 kW CCR · ABOUT 556 V OUT 2,700 W 300 671 W 3,671 W 49% OF RATING CABLE LOSS · ABOUT 18% OF THE LOAD 2 · LED, CCR UNCHANGED 7.5 kW CCR · ABOUT 218 V OUT 600 W 169 671 W 1,440 W 19% OF RATING CABLE LOSS STAYS AT 671 W · NOW ABOUT 47% CHECK THE CCR'S MINIMUM LOADING AND REGULATION 3 · LED, CCR RE-SIZED 2.5 kW CCR · ABOUT 218 V OUT 600 W 169 671 W 1,440 W 58% OF RATING FIXTURES TRANSFORMER LOSS CABLE I²R LOSS · SAME CURRENT, SAME LOOP HOW TO RE-SIZE 1 · RE-ADD THE LOAD FIXTURES, TRANSFORMERS, CABLE 2 · COMPARE RATING AND MINIMUM LOADING 3 · CHOOSE KEEP, BALANCE, COMBINE, RE-SIZE 4 · PROVE IT CURRENT AND LIGHT AT EVERY STEP THE CABLE LOSS DOES NOT FALL WITH THE LAMPS · ADD UP THE NEW LOAD, DO NOT SCALE THE OLD ONE
Figure 13. Horizontal bars on one power scale showing the load of the same 60-fixture series circuit in three states, split into fixture power, transformer loss and cable loss.
AGL Visual Encyclopedia: LED Power-Draw and CCR Re-sizing After Retrofit LED Driver Interaction with Thyristor CCR CCR loading limits and minimum-load issues
Photometry

CCR and AGL Photometry

Complementary, not interchangeable.

CCR Current
Isolation Transformer
Fixture Electrical Input
Light Source Output
Photometric Performance

Photometric performance is not controlled by current alone — optical condition, lens condition, alignment, colour, contamination, fixture age and LED/lamp condition all matter. A fixture may receive the correct current and still fail photometry; a photometric problem may also come from an electrical fault upstream.

AGL PhotometryPhotometric Testing Guide
Troubleshooting

CCR Troubleshooting Method

The location where the symptom appears is not necessarily where the fault originates.

1. Check the CCR

Input power, status, selected intensity, output current and voltage, fault indication, local/remote mode.

2. Check the series circuit

Continuity, open circuit, ground fault, cable condition, circuit configuration.

3. Check the isolation transformer

Primary and secondary connection, condition, correct rating, insulation, moisture ingress.

4. Check connectors

Primary and secondary connectors, plug/receptacle condition, moisture, mechanical damage.

5. Check the fixture

Lamp/LED, optical system, internal wiring, lens, housing, physical condition.

6. Retest

Confirm CCR current, operation, fixture operation and monitoring; photometry where applicable.

Single-light fault → investigate local components first (secondary connector, transformer, fixture). Multiple-light fault → investigate common upstream components first (CCR, series circuit, primary cable, common switching, control system). Replacing components based only on visual symptoms is far less reliable than measuring.

CCR Troubleshooting

CCR TROUBLESHOOTING · SYMPTOM, FIRST CHECK, LIKELY AREASYMPTOMFIRST CHECKLIKELY AREANO DISPLAY, WON'T STARTNothing lit on the CCRSupply, input protection, control powerPOWER INPUTRUNS, NO OUTPUT CURRENTOpen-circuit alarmCircuit side first, then CCR outputCIRCUITTRIPS OR EARTH-FAULT ALARMProtection operatesCircuit insulation, then CCR output stageCIRCUIT / CCRCURRENT WRONG FOR THE STEPReading differs from expectedStep setting, controller, thyristor, measurementCONTROLOVER-TEMPERATURE ALARMCCR running hotCooling, airflow, ambient, load ratingCOOLINGIGNORES REMOTE COMMANDSLocal panel worksSelector, communication, ALCMS linkCONTROL PATHALWAYSREAD THE DISPLAY AND ALARM FIRST · TELL ATC · ISOLATE AND PROVE DEAD BEFORE OPENING THE CABINETThe CCR holds high voltage inside and drives high current into the circuit. Authorised personnel only, using the manufacturer’s procedure.
Figure 14. CCR troubleshooting map.
AGL Visual Encyclopedia: CCR Troubleshooting CCR Failure Modes Fault-Isolation Flowchart
Diagnostic Matrix

CCR Troubleshooting Matrix

A first-level tool; final diagnosis needs measured values and the manufacturer's service procedure.

SymptomPossible causes
CCR will not startInput supply, control circuit, protection, interlock
CCR trips immediatelyOpen/abnormal circuit, over-current, protection operation
Low output currentRegulation problem, sensing, input, circuit condition
High output voltageHigh circuit impedance, open circuit, reduced load
Several lights not workingSeries circuit, transformer, connector, CCR
One light not workingTransformer, connector, secondary circuit, fixture
Remote control not workingControl wiring, interface, ALCMS, relay
Wrong brightnessCurrent-step setting, CCR control, fixture compatibility
Unstable operationCCR problem, abnormal load, LED compatibility
Repeated circuit faultsCable, connector, transformer or environmental problem
Photometric low intensityCurrent, transformer, fixture, optics or contamination
CCR FailuresSeries Circuit FaultsTroubleshooting EngineDecision Calculator
Fault Finding

Airport Lighting Fault Finding: Detection, Diagnosis, Earth Fault & Short Circuit

How a fault is noticed, located and confirmed, using the CCR as the starting point.

How Is an Airport Lighting Fault Found?

Start with where the symptom appears, which is not necessarily where the fault originates. One light out points to local components first: the secondary connector, transformer and fixture. Several lights out point to common upstream items first: the CCR, series circuit, primary cable, common switching and control system. Then follow the electrical path and measure at each point, because replacing parts on visual symptoms alone is far less reliable.

Airport Lighting Fault Detection

Airport lighting fault detection depends on the equipment and specification. A CCR with monitoring may detect input power loss, protective shutdown, significant series-circuit load loss, failure to maintain the selected current and lamp-load failure conditions, and report them to the control system. See ALCMS for how these signals reach the operator.

Airport Lighting Fault Monitor

An airport lighting fault monitor is the monitoring function, in the CCR or the control and monitoring system, that reports status, alarms and fault codes. There is no universal fault-code language, so always use the manufacturer's fault-code table. A monitor shows that a fault exists and roughly where, and it does not replace measurement in the field.

Airport Lighting Fault Diagnosis

Airport lighting fault diagnosis turns the symptom into a cause. Check the CCR first, then the series circuit, the isolation transformer, the connectors and the fixture, and retest. Final diagnosis needs measured values and the manufacturer's service procedure. A high output voltage by itself does not mean the CCR is defective, so compare output voltage with output current.

Airport Lighting Earth Fault

An airport lighting earth fault, also called a ground fault, is an unintended path from the series circuit to earth. When checking the series circuit, look at continuity, open circuit, ground fault and cable condition, and check the transformer and connectors for moisture ingress and insulation condition.

Airport Lighting Short Circuit

An airport lighting short circuit, or over-current condition, can come from a wiring fault, incorrect connection, damaged equipment, a circuit fault, an internal CCR malfunction or a switching abnormality. The CCR protection may operate. Never bypass CCR protection during troubleshooting.

Series Circuit FaultsTroubleshooting Engine

Earth Fault

SERIES LOOP · EARTH FAULT (CONDUCTOR TO GROUND) ISOLATE & LOCK OUT BEFORE TOUCHING CABLE ENDS LIVE CCR LOOP CLOSED T1 T2 T3 T4 EARTH 1 CCR LOOP IS NOT EARTHED 2 INSULATION FAILS TO EARTH 3 LIGHTS STAY ON loop unbroken 4 CAUSES: DAMAGED CABLE · WET CONNECTOR · DEGRADED PRIMARY INSULATION ONE EARTH FAULT OFTEN UNNOTICED Found by testing or monitoring SECOND EARTH FAULT SECTION BYPASSED Current returns through the ground SCHEMATIC · LOOP SHORTENED · NOT TO SCALE
Figure 15. Diagram of an earth fault in an airfield series lighting loop: insulation fails between the loop conductor and earth between transformers T2 and T3, leaking current to ground, while the loop stays closed and all lamps stay lit.
AGL Visual Encyclopedia: Earth Fault Ground-Fault Detection and Insulation Monitoring Earth-Fault Troubleshooting
Field Examples

Practical Fault Examples

The location where the symptom appears is not necessarily the location where the fault originates — follow the complete electrical path.

One runway light is not operating

Start at the fixture and work back along the path:

  • Is the fixture physically intact?
  • Is the secondary connection secure?
  • Is the transformer healthy?
  • Is the primary connection intact?
  • Is the series cable continuous?
  • Is the CCR delivering the correct current?
  • Is the circuit correctly commanded by the control system?

A complete section of lights is not operating

First question: is the problem individual or common?

  • Many lights failing together → common upstream items first: CCR, series circuit, primary cable, common switching, control system, upstream connection
  • Only one fixture failing → local items first: secondary connector, transformer, fixture, local connection
This approach prevents unnecessary replacement of expensive components.

CCR Fault-Finding Logic

CCR fault
Input
Control
Current
Voltage
Protection
Series circuit
Transformers
Connectors
Fixtures
Retest

A systematic process is much more reliable than replacing components based only on visual symptoms.

Maintenance

CCR Preventive Maintenance

Follow the airport maintenance programme and the manufacturer's instructions.

Electrical

  • Input, output and control terminals
  • Grounding and connections
  • Protection devices

Mechanical

  • Cabinet and fasteners
  • Door seals and mounting
  • Corrosion

Thermal

  • Cooling and ventilation
  • Fans where fitted
  • Hot spots and internal temperature

Control

  • Local and remote operation
  • Brightness steps
  • Display, push buttons, selector switches

Monitoring

  • Alarm functions
  • Fault indications
  • Remote status and series-circuit monitoring

CCR Maintenance

CCR IN SERVICE · WHAT CCR MAINTENANCE CHECKSCCR 5.0 ASTEP 3 · NORMALVENTS & FILTERCONTROLLER & ALARMSINPUTOUTPUTTO SERIES CIRCUITMAINS1ISOLATE & PROVE DEADlock out input, prove dead, discharge2CLEAN & COOLenclosure, filters, fans, moisture3TERMINATIONStight, clean, no heat discolouration4CONTROLS & ALARMSdisplay, steps, local and remote5OUTPUT CHECKcurrent per step against rating6RECORD & RESTOREreadings, defects, return to service1 · Isolate & prove dead2 · Clean & cool3 · Terminations4 · Controls & alarms5 · Output check6 · Record & restore
Figure 16. Constant current regulator cabinet with a display, ventilation grille, input terminals and output terminals feeding a series circuit, with six numbered maintenance checks: isolate and prove dead, clean and cool, terminations, controls and alarms, output check, and record and restore.
AGL Visual Encyclopedia: CCR Maintenance CCR Inspection CCR Cooling System
Commissioning

CCR Commissioning Procedure

The exact sequence must follow the approved commissioning procedure for the installed equipment.

1. Document Review

2. Visual Inspection

3. Input Power

4. Grounding

5. Control Wiring

6. Series Circuit

7. CCR Start-Up

8. Current Steps

9. Output Voltage

10. Local Control

11. Remote Control

12. Protection Test

13. Monitoring Test

14. Fixture Operation

15. Photometric Verification

16. Final Documentation

Installation & CommissioningTesting & Commissioning Manual

CCR Testing

CCR ON TEST · WHAT CCR TESTING PROVESINPUT SUPPLYV · phasesCCRSTEP 1-5PROTECTIONArmsINSULATIONTESTERSERIES CIRCUITor DUMMY LOADEARTH1PREPARE & ISOLATEpermit, lock out, prove dead, fit test gear2INPUT SUPPLYvoltage and phases within limits3INSULATION RESISTANCEoutput circuit tested de-energised4OUTPUT CURRENTeach brightness step vs rated value5LOAD REGULATIONcurrent holds as load or supply varies6PROTECTION & ALARMSopen circuit, overcurrent, earth leakage1 · Prepare & isolate2 · Input supply3 · Insulation resistance4 · Output current5 · Load regulation6 · Protection & alarms
Figure 17. Constant current regulator on test with an input supply meter, an insulation tester and a true-RMS current meter on the output feeding a series circuit or dummy load, with six numbered checks: prepare and isolate, input supply, insulation resistance, output current, load regulation, and protection and alarms.
AGL Visual Encyclopedia: CCR Testing CCR Output Measurement Insulation-Resistance Testing
Checklist

CCR Commissioning Checklist

Tap to tick items off.

Documentation

Approved CCR datasheet and manufacturer manual
Approved wiring diagram and series-circuit schematic
Load schedule and factory test documents
Test-equipment calibration certificates
0 / 4 complete

Physical Installation

CCR installed, cabinet condition acceptable
Input and output connections completed
Grounding and surge protection completed
Control and monitoring wiring completed
0 / 4 complete

Electrical & Control Tests

Input voltage and frequency verified
Output current and voltage verified
Protection tested and current steps verified
Local, remote, brightness and alarm tests done
0 / 4 complete

AGL System

Series circuit operating
Isolation transformers verified, connectors inspected
Fixtures operating, abnormal fixtures investigated
Photometry completed where required
0 / 4 complete
Safety

CCR Safety

High voltage and significant electrical energy.

Identify equipment
Isolate energy
Apply LOTO
Verify safe
Do the work
Test
Restore

Only appropriately trained and authorized personnel, using the airport's electrical safety procedures and the manufacturer's instructions. Take particular care with the CCR output and the series circuit: output voltage can vary significantly with circuit condition. Test instruments must be rated for the system and used per the approved test procedure.

Tools & Records

Testing Instruments & Documentation

Test instruments (per procedure)

True-RMS current and voltage measurement, insulation-resistance tester, continuity tester, earth/ground test equipment, power analyser where required, thermographic equipment, control-signal test equipment.

CCR file

Datasheet, manual, wiring diagram, schematic, nameplate, circuit ID, current-step settings, test, protection, monitoring and remote-control results, fault history, maintenance and calibration records, as-built drawings.

Pitfalls

8 Common CCR Engineering Mistakes

1. Treating the CCR like a fixed-voltage supply

It is fundamentally a current-regulating device.

2. Looking only at the fixture

The fault may be upstream.

3. Ignoring transformer losses

Consider the complete series-circuit load.

4. Using generic current settings

Verify the actual CCR configuration.

5. Ignoring LED compatibility

LED fixtures can behave differently from traditional lamps.

6. Replacing before measuring

Electrical measurements should guide diagnosis.

7. Ignoring historical fault patterns

Repeated failures can indicate a common circuit or equipment problem.

8. Treating control faults as power faults

The regulator may be healthy while the control interface is defective.

Quick Reference

CCR Working Principle — Quick Reference

ParameterBasic principle
Main functionMaintain controlled series current
Common AGL current6.6 A
Output voltageVaries according to circuit load
BrightnessControlled through current steps
Primary circuitSeries connection
TransformerProvides fixture-side electrical isolation
Fixture supplyTransformer secondary
ControlLocal and/or remote
MonitoringAvailable on monitored systems
TroubleshootingCCR → cable → transformer → connector → fixture
PhotometrySeparate optical performance verification
AGL Engineering Hub

Explore the AGL Engineering Knowledge Hub

Fundamentals

All About AGL How Airfield Lighting Works Physics of AGL AGL Components Airfield Lighting Colour Codes LED Airfield Ground Lighting LED Benefits, Lifespan & Energy Savings Solar AGL (SAGL) Portable AGL (PAGL) Advantages & Disadvantages by System Type Sustainability in AGL

Standards & Compliance

ICAO Annex 14 AGL Requirements ICAO Aerodrome Lighting Requirements FAA AC 150/5340 Series EASA CS-ADR-DSN Compliance NOTAMs

Runway, Taxiway & Approach Lighting

Runway Lighting Systems Taxiway Lighting Systems Airport Approach Lighting Systems Approach Lighting Systems Apron Lighting & Stand Guidance Apron Floodlighting Design & Lux Levels VDGS: Visual Docking Guidance Obstruction Lighting & Marking Airfield Signage & Guidance Signs Markings & Signage Integration

Surface Movement & Safety

Follow the Greens Runway Guard Lights & Stop Bars Runway Incursion Prevention & SMGCS A-SMGCS ALCMS

PAPI

How Does PAPI Work? PAPI Engineering Guide ICAO PAPI Requirements PAPI Installation & Aiming PAPI Calibration & Alignment PAPI Alignment & Maintenance PAPI Maintenance Checklist

Electrical Engineering & Power

AGL Design & Electrical Engineering Diagrams, Schematics & Wiring CCR Working Principle CCR Deep Dive AGL Isolating Transformers Airport Isolating Transformer Junction Box & Transformer Housing Cables & Connector Engineering Electrical Architecture & Redundancy Emergency Backup Power Emergency Power & Lighting Systems Surge Protection & Lightning Mitigation Lightning & Surge Protection for Circuits

Photometry & Testing

AGL Photometry Photometric Testing Guide Photometric Testing Procedure Runway Lighting Photometry Taxiway Lighting Photometry AGL Testing & Inspection Installation & Commissioning Testing & Commissioning Guide

Maintenance, Inspection & Safety

Preventive & Corrective Maintenance Maintenance Schedule & Checklist Inspection, Maintenance & Audit Checklists How to Inspect & Replace Airfield Lights Common Failure Causes & Fixes Outage Response & Runway Closure Maintenance Work Safety: LOTO, Permits, PPE

Resources, Documentation & Careers

Datasheets, Catalogues & PDF Guides Project Documentation: ITP, As-Built, O&M Engineer & Technician Job Description / Salary
FAQ

Frequently Asked Questions

Q1What is a Constant Current Regulator in airport lighting?

A CCR is an electrical power-control device that regulates current through a series-circuit AGL system.

Q2How does a CCR work in airport lighting?

The CCR measures and controls the output current so that the selected current level is maintained. Its output voltage varies according to the electrical load of the series circuit.

Q3Why does airport lighting use a CCR?

A CCR allows many AGL fixtures to operate on a common series circuit while providing controlled lighting intensity.

Q4What is the common AGL CCR current?

6.6 A is a widely used AGL series-circuit current. Other current classes and configurations are also used.

Q5What is a CCR series circuit?

A continuous AGL circuit in which the CCR supplies controlled current through primary cables and the primaries of isolation transformers.

Q6What does the isolation transformer do?

It electrically separates the series primary circuit from the secondary side feeding the individual AGL fixture.

Q7Why does CCR output voltage change?

Because the CCR regulates current. The voltage required depends on the total impedance of the connected series circuit.

Q8What are CCR brightness steps?

Predefined CCR current settings used to provide different lighting intensity levels.

Q9What is an L-828 CCR?

An L-828 is a constant current regulator without integral monitoring under the FAA equipment classification.

Q10What is an L-829 CCR?

An L-829 is a constant current regulator with monitoring under the FAA equipment classification.

Q11What is an L-827?

L-827 is the FAA designation associated with a regulator monitor.

Q12What are CCR fault codes?

Indications generated by a particular CCR to identify abnormal operating conditions. The exact codes differ by manufacturer.

Q13What causes a CCR to trip?

Possible causes include abnormal output conditions, over-current, open-circuit conditions, protection activation, internal faults or control problems.

Q14What causes low CCR current?

Possible causes include regulator faults, sensing issues, supply problems, protection operation or abnormal circuit conditions.

Q15What causes high CCR output voltage?

Possible causes include high circuit impedance, an open or partially open series circuit, disconnected loads, transformer problems or regulator malfunction.

Q16How is CCR efficiency calculated?

Output Power ÷ Input Power × 100. The required performance depends on the applicable specification and equipment design.

Q17Can CCRs operate with LED AGL fixtures?

Yes, but compatibility must be verified. LED fixtures can have different electrical characteristics from traditional incandescent loads.

Q18Is CCR testing the same as photometric testing?

No. CCR testing evaluates electrical power regulation and control. Photometric testing evaluates the optical performance of the lighting fixtures.

Q19How do I troubleshoot an airport lighting circuit?

Start with the CCR, verify current and voltage, then trace the series circuit through the cable, connectors, isolation transformers and light fixtures.

Related

Related AGL Engineering Pages

Continue learning.

PHOTOMETRY

AGL Photometry & Photometric Testing

Open →
TRANSFORMERS

AGL Isolating Transformers

Open →
CABLES

AGL Cables & Connectors

Open →
TESTING

AGL Testing & Inspection

Open →
CONTROL

ALCMS: Control & Monitoring

Open →
PAPI

PAPI Engineering Guide

Open →
RUNWAY

Runway Lighting Systems

Open →
TAXIWAY

Taxiway Lighting Systems

Open →
DEEP DIVE

CCR Deep Dive

Open →
ARTICLE

How a CCR Works

Open →
COMPARISON

CCR vs Conventional Power Supply

Open →
COMPARISON

Series vs Parallel Circuit

Open →
COMPARISON

CCR Testing vs Series Circuit Testing

Open →
CAREER

CCR Career Questions

Open →

Understand the current. Understand the circuit. Diagnose the system.

CCR controls current. The series circuit determines voltage. Isolation transformers feed individual fixtures. Control systems select the operating condition. Monitoring identifies abnormal conditions. Testing verifies the complete system.

CCR Deep Dive AGL Electrical Services
Field Insight

Engineering & Expert Notes

RS
By Rahul Sharma
Airfield Ground Lighting Specialist
Learn What Is Regulated
Principle

The CCR regulates current in the series circuit. This is why changes in load do not alter lamp current in a healthy circuit.

Brightness Steps Map to Current Settings
Steps

Confirm the actual output at each step rather than assuming the control panel setting is correct.

Check Connections at the CCR Terminals
Wiring

Loose or overheated terminals cause faults and heat. Inspect and torque according to manufacturer guidance.

Understand Fault Indications
Faults

Know what each alarm means and how to respond safely before touching the circuit.

Keep Cooling Paths Clear
Maintenance

Dust and blocked ventilation are common causes of overheating. Include cleaning in preventive maintenance.

Keep Settings and Test Data on File
Records

Record output measurements and settings so changes can be detected.

Precision AGL Academy

Understand AGL. Build Your Engineering Skills.

You now understand how a CCR controls current through an AGL series circuit and why that matters for design, commissioning and troubleshooting.

Take the next step with Precision AGL Academy.

Learn AGL Step by Step

Build your knowledge through structured technical learning covering:

AGL Fundamentals Components Electrical Systems Design Photometry Testing Troubleshooting Maintenance

Move from understanding how AGL works to developing the practical knowledge needed to analyse, operate and maintain complete AGL systems.

Explore AGL Academy Start Your Learning Journey
Understand the system. Build the knowledge. Apply the engineering.

Talk to Precision AGL Academy

Call+91 98214 96412
Emailprecisionaglacademy@gmail.com

Follow the Academy

YouTube@precisionaglacademy LinkedInPrecision AGL Academy Instagram@PrecisionAGLAcademy Facebook@PrecisionAGLAcademy