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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 ↓
PRECISION AGL ACADEMY · Component Deep Dive

Constant Current Regulators (CCR) — Deep Dive

Control the Current Control the Circuit Control the Light

A Constant Current Regulator is one of the most important electrical components in an Airfield Ground Lighting system. It supplies and controls the current in the airport series circuit so that connected lighting equipment operates at the intended intensity levels — the controlled electrical source at the beginning of the AGL series circuit, and the interface between the airport electrical supply, the series circuit, the isolation transformers and the individual light fixtures.

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Overview

What Is a Constant Current Regulator?

A Constant Current Regulator (CCR) is an electrical power-control device designed to maintain a controlled output current for an AGL series circuit.

Unlike a conventional voltage source, the CCR regulates current as the primary controlled output parameter. A CCR is not simply a power supply — it is a controlled current-regulating system, and the internal technology used to achieve that regulation can vary by design.

The FAA currently lists AC 150/5345-10H as the active specification for Constant Current Regulators and Regulator Monitors.

Typical AGL Architecture

Airport Power Supply
CCR
Series Circuit Cable
Isolation Transformers
Light Fixtures

The CCR Directly Influences

Series-circuit currentLight intensityCircuit operating conditionBrightness stepsCircuit monitoringFault detectionOverall AGL electrical performance
Working Principle

CCR Working Principle: How Does a CCR Work in Airport Lighting?

The CCR airport lighting working principle comes down to one idea: sense the output current and adjust the voltage to hold it at the target for the selected brightness step.

1. AC Input

The CCR takes its power from the airfield AC supply. The input can vary, and the CCR is designed to keep its output steady regardless.

2. Brightness Step Reference

A local or remote control command selects a brightness step. Each step corresponds to a defined target output current.

3. Regulation

The CCR adjusts its output voltage so that the current stays at the target, whatever the load on the circuit happens to be.

4. Series Loop Output

The regulated current flows around the series loop, so the same current passes through every isolation transformer on the circuit.

5. Feedback

The CCR continuously measures its output current and compares it with the target, correcting any difference.

6. Protection & Monitoring

The CCR detects abnormal conditions such as open circuit, overcurrent, earth fault or overtemperature, and reports them to the operator.

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 1. 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
Fundamental Principle

Why Does AGL Use Constant Current?

AGL series circuits may contain a large number of lighting fixtures distributed over long distances. The electrical characteristics of the circuit can change because of the number of fixtures, transformer characteristics, cable impedance, cable length, temperature, fixture condition, open circuits, short circuits, insulation deterioration and component failures. A conventional constant-voltage supply would not provide the same controlled current behaviour under these changing conditions — so the CCR is designed to regulate the series-circuit current instead.

CCR Output Current
Series Circuit Current
Transformer Input
Fixture Operation
Optical Output
System View

The CCR in the Complete AGL System

The CCR should always be understood as part of a complete system — the electrical chain runs from the incoming supply through to the aircraft's visual guidance. The same basic architecture may serve runway, taxiway, approach or other series-circuit lighting applications depending on the system design.

INCOMING AC SUPPLY
PROTECTION & SWITCHING
CONSTANT CURRENT REGULATOR
SERIES CIRCUIT CABLE
PRIMARY CONNECTOR
ISOLATION TRANSFORMER
SECONDARY CONNECTOR
AGL LIGHT FIXTURE

CCR Location

RUNWAY STRIP RUNWAY TAXIWAY TERMINAL / APRON ILS CRITICAL AREA RUNWAY CIRCUIT LOOP TAXIWAY CIRCUIT LOOP to approach / PAPI AIRFIELD LIGHTING VAULT CCR 1 · RUNWAY CCR 2 · TAXIWAY CCR 3 · APPROACH CONTROL / ALCMS PANEL UTILITY SUPPLY + STANDBY GENERATOR / UPS ATC TOWERcontrol room ALCMS CONTROL AND MONITORING LINK 1 2 3 4 5
Figure 2. Plan view of an airfield showing where the CCR is located.
AGL Visual Encyclopedia: CCR Location CCR System Overview CCR-to-Series-Circuit Interface
Core Responsibilities

Main Functions of a CCR

Current Regulation

Maintains the commanded series-circuit current.

Brightness Control

Provides selectable or controlled current levels for different lighting intensities.

Circuit Energization

Supplies power to the complete series circuit.

Circuit Monitoring

Operating conditions and faults can be monitored, depending on configuration.

Protection

Incorporates protection and control functions appropriate to its design and specification.

Remote Control

Airport lighting control systems can command the required CCR operating level.

Common Misunderstanding

A CCR Is Not a Conventional Transformer

"A CCR is just a transformer that supplies the runway." — It is not.

A CCR is a controlled current-regulating system. Its function is to regulate the output current despite changes in circuit conditions within its designed operating range. The internal technology can vary according to the CCR design, so it should never be assumed solely from the term "CCR."

Internal Technology

Major CCR Technologies

Historically and commercially, CCR technology has included several distinct approaches.

Saturable Reactor Type

Older CCR designs that use magnetic saturation and reactor control principles.

Ferroresonant Type

Designs that use magnetic components and resonance characteristics to regulate the output.

Static / Electronic CCR

Modern regulators using semiconductor power electronics, control electronics and digital monitoring.

Hybrid Designs

Some systems combine magnetic and electronic technologies.

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 3. 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
FAA Classification

L-828, L-829 & AC 150/5345-10H

In FAA terminology, L-828 and L-829 are important CCR classifications. The distinction is primarily associated with the regulator and monitoring/control functionality specified for airport lighting applications.

For any project, the exact equipment type, features and certification requirements should be checked against the applicable current FAA specification and project requirements. FAA AC 150/5345-10H is the current active FAA specification covering CCRs and regulator monitors.

FAA Constant Current Regulator

The FAA constant current regulator specification is AC 150/5345-10H, which covers CCRs and regulator monitors. L-828 and L-829 are the FAA classifications. Check the equipment type and certification against the current circular and the project requirements.

Interactive

CCR Brightness Step Simulator

AGL lighting intensity is controlled by changing the series-circuit current: higher current gives higher light output, lower current gives lower light output. Drag the step slider to see the concept — the relationship between electrical current and optical intensity is equipment-dependent and must be verified against actual fixture and photometric data.

Step 3 of 5
Relative CCR Current
Higher
Relative Lighting Output
Increased Intensity
Typical Use
Normal Visibility

This is an illustrative concept model, not a design or acceptance tool. Actual current values for each step must come from the applicable CCR, lighting system and project requirements.

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 4. 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
Why It Matters

Why Current Control Is Critical

Consider a runway lighting circuit — if the CCR output drifts from its intended level, the consequences run in both directions.

Output Lower Than Intended

  • Fixtures may appear dim
  • Photometric performance may be reduced
  • System visibility may be affected
  • A fault may exist in the regulator or circuit

Output Higher Than Intended

  • Fixture loading may increase
  • Equipment stress may increase
  • Optical output may exceed its intended operating condition
  • Protection or monitoring functions may operate

CCR current verification is an essential part of AGL testing.

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 5. 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
Electrical Behaviour

CCR Output Voltage — Current Controlled, Voltage Adapts

The CCR does not simply provide a fixed output voltage. The required output voltage varies with the electrical characteristics of the connected series circuit — as the circuit load changes, the CCR develops the voltage necessary to maintain the commanded current, within its designed operating limits.

SystemControlled ParameterBehaviour
Constant Voltage SystemVoltageVoltage controlled → Current varies
AGL Series CircuitCurrentCurrent controlled → Voltage adapts to circuit condition
Current vs Voltage as Circuit Load Changes

As circuit resistance (more fixtures, longer cable, ageing connections) increases, the CCR raises its output voltage to hold current flat — the opposite of a constant-voltage supply

Circuit resistance (more load / longer cable) → Output value → CURRENT — held constant VOLTAGE — rises to compensate Light load Heavy load / long cable
Fault Conditions

Open Circuit, Short Circuit & Earth Fault

Click a card to see possible causes. Never assume that an abnormal voltage or current reading has one universal value — always confirm against the CCR manufacturer's documentation and applicable standard.

Open-Circuit Condition

Possible Causes

  • Broken cable
  • Disconnected connector
  • Failed isolation transformer
  • Loose connection
  • Damaged termination
  • Open fixture circuit

Short-Circuit Condition

Possible Causes

  • Cable insulation failure
  • Water ingress
  • Damaged connector
  • Incorrect termination
  • Failed component
  • Cable-to-ground fault

Earth Fault

Possible Causes

  • Cable insulation damage
  • Water ingress
  • Damaged connector
  • Transformer insulation failure
  • Fixture wiring fault
  • Joint failure

Open-Circuit Symptoms

Possible Symptoms

  • High output voltage
  • Circuit fault indication
  • Regulator trip
  • Current reduction
  • Unstable output
  • Alarm condition

Water ingress can create a chain reaction: Insulation degradation → Leakage current → Earth fault → Circuit instability → Fixture failure. Short-circuit investigation should therefore begin at the regulator and progress into the field circuit.

Three Fault Types on the Same Loop

Open circuit breaks the current path entirely; short circuit bypasses the load; earth fault leaks current to ground — each produces a different CCR response

CCR OPEN CIRCUIT Break in the path → current drops to zero, voltage rises to its limit SHORT CIRCUIT Direct path bypasses load → voltage collapses at that point, current seeks the short EARTH FAULT Leakage current to ground → earth-fault alarm, possible instability

Airport Lighting Open Circuit

An airport lighting open circuit breaks the series loop, for example through a broken cable, a disconnected connector or a failed transformer. The CCR may show a high output voltage, trip or give a fault indication. Locate the break by splitting the loop and testing continuity, and never open an energised circuit.

Diagnostic Starting Points

The CCR Current-Voltage Relationship

A useful diagnostic principle — these are starting points for investigation, not universal fault rules.

Current Normal + Voltage Normal

Likely healthy electrical operating condition.

Current Low + Voltage Abnormal

Investigate regulator or circuit condition.

Current Normal + Voltage Unusually High

Investigate circuit loading / open-circuit conditions.

Current Unstable + Voltage Unstable

Investigate CCR regulation, control, input supply or circuit faults.

Circuit Diagram

CCR Circuit Diagram, CCR Wiring & Series Circuit Design

A CCR circuit diagram shows how the regulator, series loop, isolation transformers and earth fit together. The same principle applies to runway, taxiway and approach circuits.

Simplified airport lighting circuit diagram: one CCR drives one series loop, and each isolation transformer feeds its own light

AC SUPPLY CCR constant current SERIES LOOP — the same current through every isolation transformer IT L IT L IT L Earth / bonding IT = isolation transformer · L = light fixture

Airport Lighting Circuit Diagram

A full airport lighting circuit diagram adds cutouts, junction boxes, switching and earthing to the simplified loop shown above. It is the key document for maintenance and fault finding.

Runway Lighting Circuit Diagram

A runway lighting circuit diagram usually shows circuits split by light type, such as edge, centreline and touchdown zone, and sometimes interleaved so that one circuit failure does not remove a whole function.

Taxiway Lighting Circuit Diagram

A taxiway lighting circuit diagram follows taxiway routes and zones, with stop bars on separately switched circuits so they can be controlled independently.

CCR Wiring

CCR wiring covers the AC input, the output terminals to the series loop, the control and monitoring connections and the earth. Follow the manufacturer's wiring diagram and keep the primary loop cabling clearly labelled.

Runway Lighting Series Circuit Design

Runway lighting series circuit design starts from the lights on the circuit, their load, the transformer ratings and the cable length. It then sizes the CCR with spare capacity. See AGL Design & Electrical Engineering.

How Is an Airport Lighting Series Circuit Designed?

List the fixtures and loads, select the CCR rating, route and size the cable, split the lights into circuits, specify earthing and protection, and verify the result by testing.

System Interfaces

CCR, Isolation Transformers, Cable & LED Compatibility

The CCR does not normally connect directly to individual AGL lamps or fixtures — the series circuit feeds isolation transformers, which electrically interface the series circuit with the individual fixture load. The CCR, cable and connected equipment must be treated as one electrical system.

CCR & Isolation Transformers

Typical path: CCR → Primary Series Cable → Isolation Transformer → Secondary Cable → Light Fixture. This allows many individual lighting units to be connected into one series circuit.

CCR & Series-Circuit Cable

Important parameters: cable length, resistance, inductive characteristics, number of transformers, transformer loading, circuit configuration, operating current, insulation condition and environmental conditions.

CCR & LED Lighting

LED fixtures changed the electrical behaviour and loading of many AGL systems. An existing CCR should not automatically be assumed compatible with every LED fixture — check current waveform, control behaviour, minimum load, harmonics and power factor.

The correct engineering question is not "Is this CCR good?" — it is "Is this CCR compatible with the complete AGL series-circuit load?"

CCR → Series Cable → Isolation Transformer → Connector → LED / Lamp Fixture — every link in this chain must be checked together.

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 6. 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 LED Power-Draw and CCR Re-sizing After Retrofit CCR output waveform distortion
Selection & Sizing

CCR Load Calculation & Rating

Before selecting a CCR, the designer should determine the expected circuit load — the regulator must be selected for the actual circuit requirements rather than simply choosing the largest available unit.

ParameterEngineering Purpose
Input voltageMatches airport supply
Input frequencyMatches electrical system
Output currentMatches series circuit
Output powerSupports circuit load
Circuit capacityDetermines usable load
Brightness stepsControls intensity
MonitoringDetects abnormal conditions
ProtectionProtects regulator/system
Control interfaceIntegrates with ALCMS/control
EfficiencyElectrical performance
Environmental ratingInstallation environment
For many airport series-circuit systems, 6.6 A is a commonly encountered nominal series-circuit current — but actual required current levels and steps depend on the applicable system design, equipment and standards. Do not treat one current value as universally applicable.

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 7. Simplified view of CCR loading limits.
AGL Visual Encyclopedia: CCR loading limits and minimum-load issues CCR Selection Circuit Load
Electrical Performance

Efficiency, Power Factor & Thermal Management

Efficiency

Affects input power, heat generation, room temperature, energy consumption and cooling requirements. Should be evaluated from actual manufacturer data rather than assumed from CCR type.

Power Factor

Poor power factor can increase input current, distribution losses, transformer loading and electrical infrastructure requirements. Acceptable limits come from the applicable specification.

Thermal Management

CCR losses become heat. An overloaded or poorly ventilated CCR may show overtemperature alarms, output instability, reduced reliability, protective shutdown or premature failure.

Command & Supervision

CCR Control, Monitoring & ALCMS Integration

A CCR can be controlled locally or remotely, and its control function should never be confused with its monitoring function.

OPERATOR / ATC / CONTROL SYSTEM
ALCMS
CCR CONTROL COMMAND
CCR
SERIES CIRCUIT
AGL FIXTURES

Controller

Commands the CCR — local operator controls, or remote commands from the ALCMS, control panel, relay/control system or automation system.

Monitor

Reports or evaluates CCR operating status — current, voltage, fault status, circuit condition, selected intensity, alarms and equipment availability.

Control → CCR → Monitor → Control System

CCR Control Architecture

CCR · CONTROL ARCHITECTURE COMMANDS DOWN · STATUS UP CONTROL POSITION TOWER / OPERATOR ALCMS CONTROL + MONITORING CCR CONTROLLER LOCAL / REMOTE POWER STAGE TO SERIES LOOP LINK LINK → COMMANDS: ON / OFF, BRIGHTNESS STEP ← STATUS: STEP, ON/OFF, ALARMS LOCAL SELECTOR 1 THE OPERATOR CHOOSES ON, OFF AND THE STEP 2 COMMANDS PASS DOWN TO THE CCR CONTROLLER 3 STATUS AND ALARMS PASS BACK UP COMMANDS ON / OFF + STEP DOWN THE CHAIN STATUS STEP, STATE, ALARMS UP THE CHAIN LOCAL / REMOTE ONE SOURCE IN CONTROL LOCAL NORMALLY TAKES PRIORITY BLOCK DIAGRAM · GENERIC · DESIGNS VARY BY SYSTEM
Figure 8. Block diagram of CCR control architecture: commands for on, off and brightness step pass from the control position through the ALCMS and a communication link to the CCR controller and power stage, status and alarms return the same way, and a local selector gives priority to local control.
AGL Visual Encyclopedia: CCR Control Architecture CCR Remote Control CCR Local Control ALCMS-to-CCR
Design for Reliability

CCR Protection Functions

Overcurrent

Protects against excess series-circuit current.

Short / Open Circuit

Protection and fault response appropriate to the specification.

Input Abnormalities

Voltage, frequency, phase and transient disturbances.

Overtemperature

Thermal protection against overload or poor ventilation.

Protection philosophy varies by CCR technology. Always use the manufacturer's protection logic when troubleshooting a specific model.

CCR Protection

TRIP SIGNAL AC SUPPLY INPUT BREAKERoverload / shortCONTACTORCLOSEDTHYRISTOR STAGEpower controlTRANSFORMERisolationOUTPUT SENSINGcurrent (CT)SERIES CIRCUITfloating loop SURGE PROTECTIONdiverts surges to earthSUPPLY MONITORover / under-voltageTEMPERATURE SENSORwarn, then tripCONTROL BOARDopens contactor on tripINSULATION / EARTH MONITORwarning only
Figure 9. CCR protection layers along the power path: surge protection, input breaker, supply monitor, contactor, thyristor stage with temperature sensor, transformer, output current sensing, series circuit and an insulation and earth monitor, all reporting to the control board
AGL Visual Encyclopedia: CCR Protection Open-Circuit Protection (OCP) CCR Alarm System
Installation Considerations

Installation Environment & Earthing

Installation Environment

  • Indoor/outdoor location
  • Ambient temperature & humidity
  • Dust & ventilation
  • Accessibility & electrical clearances
  • Cable entry & maintenance access
  • Fire protection & water ingress

Earthing & Bonding

  • Personnel safety
  • Fault-current paths
  • Equipment protection
  • Surge protection
  • Lightning protection
  • Electromagnetic compatibility
Earthing & Insulation Tests

Airport Lighting Earth Test, Megger Test, Surge Protector & Lightning Arrester

Earthing and insulation tests show whether the series circuit and the CCR installation are safe and healthy, and surge protection limits the damage from transients.

TestWhat it checksNote
Airport lighting earth testThe resistance of the earth connection of the CCR installation and associated equipmentResult compared with the specification
Runway lighting earth testThe earthing arrangement for runway lighting circuits and equipmentRecorded with the circuit
Taxiway lighting earth testThe earthing arrangement for taxiway lighting circuits and equipmentRecorded with the circuit
Runway lighting megger testInsulation resistance of the runway series circuit to earthCircuit isolated and CCR disconnected first
Airport series circuit insulation testInsulation of the whole series loop to earth, trended over timeA falling trend can warn of water ingress
Airport cable megger testInsulation of the primary cable, for example before equipment is connectedRepeat periodically and after repairs
Test methods, test voltages and acceptable values come from the CCR manufacturer, the specification and the applicable standard. Always isolate, lock out and prove dead before testing.

What Is Airport Lighting Earth Testing?

Airport lighting earth testing measures how well the installation is connected to earth, so that fault current has a safe path and protective devices and surge protection work as intended.

Airport Lighting Surge Protector

An airport lighting surge protector limits transient overvoltages on the supply and series circuit, protecting the CCR, transformers and control equipment.

Airport Lighting Lightning Arrester

An airport lighting lightning arrester diverts lightning-induced surges to earth. It depends on a low-resistance earth path, so earth testing and surge protection belong together.

Runway Lighting Earth Test & Taxiway Lighting Earth Test

The runway lighting earth test and taxiway lighting earth test check the earthing of each circuit's equipment, so fault current has a safe path and protection works as intended. Record the result with the circuit and compare it with the specification.

Runway Lighting Megger Test & Airport Cable Megger Test

The runway lighting megger test measures the insulation resistance of the runway series circuit to earth, with the circuit isolated and the CCR disconnected first. The airport cable megger test does the same for the primary cable, for example before equipment is connected, and is repeated periodically and after repairs.

Airport Series Circuit Insulation Test

The airport series circuit insulation test measures the insulation of the whole loop to earth. Trend the results over time, because a falling trend can warn of water ingress before it becomes an earth fault.

Isolating Transformer Insulation Test

The isolating transformer insulation test checks the insulation between the primary and secondary windings and from the windings to earth, with the transformer disconnected from the circuit. Test voltage and acceptable values come from the manufacturer and the specification.

Airport Lighting Cable Insulation

Airport lighting cable insulation keeps the series-circuit conductor separate from earth. It degrades through water ingress, damage during installation or repair, ageing and poor connector or splice work, and insulation resistance tests on the primary cable show its condition.

What Is Airport Lighting Insulation Testing?

Airport lighting insulation testing measures the insulation resistance of cables, connectors and transformers, usually with a megger, to confirm they isolate the series circuit from earth. It is done at commissioning, periodically and after repairs, with the circuit isolated and locked out.

Runway Lighting Circuit Resistance

Runway lighting circuit resistance is the resistance of the series loop conductor, measured with the circuit isolated and compared with the commissioning baseline. A rising trend can show degraded connections, which makes the CCR raise its output voltage to hold the current.

Surge Protection Devices for CCR and Circuits

SCHEMATIC · WHERE SURGE PROTECTION DEVICES SIT ON A CCR AND ITS SERIES CIRCUIT EARTHING NETWORK · ONE BONDED SYSTEM EARTHING NETWORK MAINSSUPPLY CONTROLAND COMMS CCRconstant current regulator SPD 1 · MAINS INPUT SPD 3 · CONTROL LINE SPD 2 · OUTPUT TO EARTH SERIES CIRCUIT · TRANSFORMERS AND LAMPS NEARBY STRIKE SURGE INDUCED IN THE CABLE SURGE ENERGY TO EARTH Each device is idle in normal service, conducts when a surge arrives, and passes the energy to the earthing network through short, direct leads.
Figure 10. Schematic of a constant current regulator with its protective devices.
AGL Visual Encyclopedia: Surge Protection Devices for CCR and Circuits Earthing Network Insulation-Resistance Testing
Current & Efficiency

CCR Current Setting, Output Current Test & CCR Efficiency

Getting the output current right at each step is what makes the lights perform as designed.

CCR Current Setting

The CCR current setting at each brightness step defines the current in the series loop. It is set and checked at commissioning and after repair, because a wrong setting changes both light output and lamp life.

CCR Output Current Test

A CCR output current test measures the loop current at each step with a calibrated instrument suited to the waveform, and compares it with the specification. Record each step, as in the table below.

Runway Lighting CCR Current

Runway lighting CCR current at each step determines the light output of the runway fixtures. Record it together with photometry, so that optical results can be tied to a known current.

CCR Efficiency

CCR efficiency is the ratio of output power to input power. It varies with loading and technology, and a CCR run well below its rating is generally less efficient. Correct sizing keeps losses and heat down.

Verification

Measuring CCR Current & Voltage

Output current is one of the most important CCR measurements — it should be stable, calibrated, repeatable and recorded for each applicable intensity step.

StepCommanded LevelMeasured CurrentStatus
1Low___ APASS/FAIL
2Step 2___ APASS/FAIL
3Step 3___ APASS/FAIL
4Step 4___ APASS/FAIL
5Maximum___ APASS/FAIL
Acceptance values must be based on the applicable CCR specification, manufacturer requirements and project criteria — never on generic assumed values.

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 11. 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 Testing CCR Power Output
Commissioning Sequence

CCR Commissioning

A CCR should be commissioned systematically, following a recommended sequence from visual inspection through to final documentation.

VISUAL INSPECTION
INSTALLATION VERIFICATION
INPUT SUPPLY VERIFICATION
EARTHING VERIFICATION
CONTROL VERIFICATION
CONTROLLED ENERGIZATION
OUTPUT CURRENT VERIFICATION
BRIGHTNESS STEP VERIFICATION
MONITORING VERIFICATION
FIXTURE OPERATION & PHOTOMETRIC VERIFICATION
FINAL DOCUMENTATION
Interactive

CCR FAT / SAT Checklist

Tick items off as you review a project. This resets on reload.

Factory Acceptance

Visual & nameplate verification
Input voltage verification
Output current verification
Brightness-step verification
0 / 4 complete

Protection & Monitoring

Regulation performance checked
Protection functions tested
Alarm functions tested
Monitoring interface verified
0 / 4 complete

Site Acceptance

Correct installation confirmed
Earthing checked
Control operation verified
Circuit operation verified
0 / 4 complete

Integration

Remote commands tested
ALCMS integration verified
Operational response confirmed
Final documentation completed
0 / 4 complete

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 12. 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
Ongoing Engineering

CCR Maintenance & Records

Visual

Enclosure, labels, connections, signs of overheating, dust, corrosion, moisture.

Electrical

Input voltage, output current, output voltage, control response, protection functions.

Thermal & Functional

Hot spots, cooling system, ventilation, brightness steps, remote control, monitoring, alarms.

Maintain historical records of CCR identification, manufacturer, model, serial number, rating, circuit served, test dates, input/output measurements, brightness-step results, alarm results, fault history and calibration information. Historical trends can reveal degradation before a major failure occurs.

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 13. 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
Faults

Airport Series Circuit Faults, Earth Faults & CCR Not Working

A structured approach to faults on the series circuit and the CCR itself. See also the troubleshooting engine.

Airport Series Circuit Fault

An airport series circuit fault is an open circuit, a short circuit or an earth fault on the loop. Each gives a different CCR response, as shown in the fault section above.

Earth Fault

An airport series circuit earth fault, also called an airport lighting earth fault, is leakage from the circuit to earth. It is normally flagged by the CCR earth fault indication, and it is usually caused by insulation damage or water ingress.

Airport Series Circuit Troubleshooting

Airport series circuit troubleshooting runs: confirm the CCR status and fault indication, measure output current and voltage, split the loop at accessible points, insulation-test each section, then repair and retest.

CCR Fault Codes

CCR fault codes are specific to each manufacturer. Read them from the display or the control system, record them with the time and step, and look them up in the manual. Typical categories are overcurrent, open circuit, earth fault, overtemperature and input abnormalities.

CCR Not Working Airport

When a CCR is not working at an airport, check the input supply, the local or remote selector, the control command, any protection trip and the output current. Do not repeatedly re-energise a circuit with a suspected earth fault.

Safety First

Isolate, lock out and prove dead before working on any series circuit or CCR. Series circuits carry constant current at potentially dangerous voltage, and an energised circuit must never be opened.

Airport Lighting Cable Fault

An airport lighting cable fault is damage to the primary cable that causes an earth fault, short circuit or open circuit. Common causes are water ingress, mechanical damage from excavation, insulation ageing and poor splices or connectors. Locate it by splitting the loop and insulation-testing each section, then repair and retest.

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 14. 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
Systematic Diagnosis

CCR Troubleshooting Framework

When a CCR problem occurs, do not immediately replace the regulator.

Observe
Measure
Compare
Separate CCR from Circuit
Isolate Fault
Rectify
Re-Test
Document

Never diagnose a CCR only from visual symptoms.

Reference

CCR Troubleshooting Table

SymptomPossible CausesFirst Checks
CCR does not startInput supply, control command, protection tripInput and control status
Output current lowCCR fault, circuit loading, configurationMeasure current and voltage
Output current highRegulation fault, configurationVerify current against required level
Current unstableCCR control fault, input disturbance, circuit issueTrend current and input
Output voltage unusually highOpen/partial circuit, loading issueCheck circuit continuity/load
Output voltage unusually lowHeavy loading, short/fault, CCR issueCheck current and circuit
One section darkLocal transformer/fixture/cable faultIsolate circuit section
Multiple fixtures darkCircuit or regulator issueCheck CCR output and circuit
Earth faultCable/transformer/connector insulation faultInsulation/earth-fault investigation
CCR overheatingOverload, ventilation, internal faultLoad and thermal inspection
Remote control failsCommunication/control circuitLocal vs remote operation
Alarm activeEquipment or circuit conditionRead fault indication/history

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 15. CCR troubleshooting map.
AGL Visual Encyclopedia: CCR Troubleshooting CCR Failure Modes CCR Fault Indication
Divide & Conquer

CCR Diagnostic Logic & Fault Isolation

A powerful troubleshooting approach is to divide the system into two sections, then determine whether the problem is a CCR problem or a field circuit problem. This prevents unnecessary CCR replacement.

Section A: CCR

  • Input
  • Control
  • Output current
  • Output voltage
  • Protection
  • Monitoring

Section B: Series Circuit

  • Cable
  • Connectors
  • Transformers
  • Fixtures
  • Insulation
  • Earth leakage

Fault Isolation Sequence

CCR Output
Series Circuit
Circuit Section
Isolation Transformer
Secondary Connector
Fixture
Section A vs Section B — Split at the CCR Output

Disconnecting the field circuit and testing the CCR against a known load (or vice versa) tells you immediately which side of this split the fault is on

SECTION A — CCR Input · control · output current/voltage · protection CCR CCR output — the split test point SECTION B — SERIES CIRCUIT Cable · connectors · transformers · fixtures · insulation XFMR Fixture
Beyond Electrical Testing

CCR & Photometry

CCR performance cannot be evaluated electrically alone. A regulator may produce the correct current while the lighting system still has poor optical performance because of a dirty lens, misalignment, an incorrect fixture, LED degradation, optical damage, wrong colour or installation geometry.

Electrical Testing ≠ Photometric Verification — both are required for complete system verification.

CCR Command
Series Current
Isolation Transformer
Light Source
Optical Output
Photometric Performance
Comparisons

CCR vs Conventional Supply, Transformer & LED Driver

FeatureConventional SupplyAGL CCR
Primary controlled quantityVoltageCurrent
Typical applicationGeneral electrical loadsSeries-circuit AGL
Long series circuitNot its normal purposeDesigned for series-circuit application
Brightness controlSeparate arrangementIntegrated/associated with CCR system
Circuit monitoringApplication-dependentIntegral/associated depending on type
Isolation transformersNot normally part of architectureFundamental to many AGL series circuits
FeatureTransformerCCR
Main functionVoltage transformation/isolationControlled series-circuit current
Output controlUsually voltage ratioCurrent regulation
AGL series circuit roleSupporting componentPrimary power-control component
Brightness controlNoYes, depending on design
System roleInterface/load componentSource/regulator

A CCR should not automatically be treated as an LED driver. An LED driver normally supplies power directly to an LED load; an AGL CCR supplies the series circuit, which may contain: CCR → Series Cable → Isolation Transformer → Fixture/Driver. The complete electrical architecture must be evaluated.

Basic Formulas

CCR Engineering Calculations

Circuit Load

Total load = Sum of connected transformer/fixture loads

Power & Apparent Power

P = V × I  ·  S = V × I  ·  For balanced three-phase: S ≈ √3 × V × I

These are basic engineering relationships. For AC systems, actual power relationships depend on power factor and waveform — actual CCR calculations must use the regulator manufacturer's data and applicable system configuration.

Review Before You Approve

CCR Design Review Questions

  1. What circuit does this CCR supply?
  2. What is the total connected load?
  3. What is the design current?
  4. What brightness levels are required?
  5. What is the maximum circuit voltage?
  6. What cable is used?
  7. How many transformers are connected, and are they compatible?
  8. Are the fixtures compatible?
  9. How is the CCR controlled and monitored?
  10. What happens during an open circuit, earth fault or short circuit?
  11. How is the CCR protected?
  12. How will output current and system performance be tested and verified?
  13. What standards and project specifications apply?
Do not ask only: "Is the CCR ON?" Ask: "Is the CCR supplying the correct controlled current, responding correctly to commands, operating within its specified limits, communicating its status, and correctly powering the complete AGL series circuit?"
CCR Overview

CCR in Airfield Lighting: Types, Sizing & Regulator Cabinet

CCR In Airfield Lighting

A CCR in airfield lighting is the regulator at the head of each series circuit. It takes the airport supply and delivers one controlled current to the loop of lights, set by the brightness step selected.

CCR Types For Airport Lighting

CCR types for airport lighting include ferroresonant and thyristor (SCR) designs, and newer solid-state types, in 3-step or 5-step versions and a range of kW ratings. See Major CCR Technologies above for how they differ.

CCR Sizing For AGL

CCR sizing for AGL adds up fixture wattage, isolating transformer losses and cable losses, then selects a rating with margin so the regulator is neither overloaded nor lightly loaded. Check the standard step current for the circuit.

Airport Lighting Regulator Cabinet

An airport lighting regulator cabinet houses the CCR in the substation. It needs clear access, adequate ventilation, a clean dry environment, correct earthing and tidy input and output cable entry.

Constant Current Regulator Working Principle

Constant current regulator working principle: it measures output current and adjusts its output voltage to hold the set current, whatever the load voltage needs, so every light in the series circuit carries the same current.

Constant Current Regulator Types

Constant current regulator types are grouped by technology (ferroresonant, thyristor, solid-state), by number of brightness steps and by rating, and by whether control is local, remote or networked.

Constant Current Regulator Functions

Constant current regulator functions are to hold the circuit current, provide brightness steps, protect the circuit against faults and report status to the control system.

Constant Current Regulator Components

Constant current regulator components include the power transformer or converter, control board, current sensing, brightness-step selector, protection devices, output terminals and control interface.

Specification & Standards

Constant Current Regulator Specification, Design, Requirements & Standards

Constant Current Regulator Specification

A constant current regulator specification states input supply, output current steps, kW rating, efficiency, power factor, protection, control interface and environmental limits, with the standard it must meet.

Constant Current Regulator Requirements

Constant current regulator requirements include accurate current regulation across the load range, protection against open circuit and earth fault, suitable control and monitoring, and compliance with the project standard.

Constant Current Regulator Design

Constant current regulator design for a project sets the rating, quantity, circuit split, redundancy and control interface, based on connected load and the operational needs of the runway or taxiway.

Constant Current Regulator Selection Guide

Constant current regulator selection guide: match rating and steps to the circuit load and standard, choose the technology for efficiency and maintainability, and check control interface compatibility.

Constant Current Regulator Technical Guide

Constant current regulator technical guide: use this page with the manufacturer manual and the circuit design to verify ratings, settings and protection before commissioning.

Constant Current Regulator Standards

Constant current regulator standards include FAA AC 150/5345-10 (L-828 and L-829), IEC 61822, ICAO Annex 14 and national requirements. See the L-828, L-829 section above.

AGL Regulatory Requirements

AGL regulatory requirements for CCRs come from ICAO Annex 14, national regulators such as DGCA in India, the airport operator, and product standards such as IEC 61822 and FAA AC 150/5345-10.

Install & Service

CCR Installation Procedure, Fault Troubleshooting, Testing & Maintenance

CCR Installation Procedure

A CCR installation procedure covers positioning and levelling the cabinet, connecting supply, output and earth cables with correct torque, checking insulation resistance of the output circuit, and verifying settings before energising.

CCR Fault Troubleshooting

CCR fault troubleshooting starts with the displayed alarm or trip, then checks supply, output current and the series circuit. An open circuit, earth fault or overload trip each point to different parts of the circuit; isolate and lock out before testing.

Constant Current Regulator Commissioning

Constant current regulator commissioning confirms correct installation, output current at each step, protection operation, control and monitoring signals, and records the results. See CCR Commissioning above.

Constant Current Regulator Testing Procedure

Constant current regulator testing procedure covers output current at every step, protection trips, control from local and remote, and insulation of the connected circuit, with readings recorded against limits.

Constant Current Regulator Maintenance

Constant current regulator maintenance includes cleaning, checking connections, verifying output current at each step, testing protection and recording results in the maintenance log.

Constant Current Regulator Preventive Maintenance

Constant current regulator preventive maintenance is a scheduled programme of inspection, cleaning, calibration checks and protection tests that keeps the regulator reliable between faults.

Constant Current Regulator Troubleshooting

Constant current regulator troubleshooting separates regulator faults from circuit faults: check supply and alarms first, then measure output current and test the circuit with the CCR isolated.

Before You Buy

CCR Selection Checklist

Before selecting a CCR, verify the following against the applicable system design and standards.

Required input voltage Frequency Number of phases Required output current Required brightness steps Connected load Series-circuit configuration Maximum circuit voltage Control method Monitoring requirements ALCMS interface Environmental conditions Earthing requirements Protection requirements LED compatibility Applicable standards Certification requirements Airport/project specifications

CCR Selection

SELECTION FLOWCHART · FOUR DECISIONS IN ORDER 1LOAD How big is the circuit? Lamps, transformers, cable → Total kW at top step Room to grow → Next standard size up 2OUTPUT What current and steps? 6.6 A series circuit → Rated output 6.6 A 3-step or 5-step → Steps match the design 3SUPPLY What feeds it? Single- or three-phase → Input matches supply Voltage and frequency → As on rating plate 4CONTROL How is it run and housed? Tower or ALCMS control → Remote interface fitted Indoor vault → Cooling suits the vault CONFIRM BEFORE ORDERING kW rating · output current and steps · input supply · control interface · cooling · standard compliance FLOWCHART · THE MANUFACTURER DATA SHEET AND STANDARD DECIDE THE FINAL CHOICE
Figure 16. Flowchart of four decisions for selecting a constant current regulator: circuit load, output current and steps, input supply, and control and location, followed by a confirmation of rating, output, input, control interface, cooling and standard compliance.
AGL Visual Encyclopedia: CCR Selection CCR loading limits and minimum-load issues
Field Reference · Interactive

CCR Inspection Checklist

Click each item as it's verified in the field.

Physical

Nameplate
Enclosure
Cable entries
Terminals & labels
Ventilation
Corrosion, moisture & physical damage
0 / 6 complete

Electrical

Input voltage & frequency
Input current
Output current
Output voltage
Power & power factor where applicable
Earthing
0 / 6 complete

Functional

Start/stop
Brightness steps
Local control
Remote control
Monitoring & alarm
Protection & fault indication
0 / 6 complete

CCR Inspection

CCR INSPECTION SAME CCR, SAME CIRCUIT, DIFFERENT CONDITION DEFECTS FOUNDSOUND CCR ALARMOVER-TEMPTERMINATIONSISOLATEDCCR · STEP 3NORMALTERMINATIONSISOLATED CLOGGED VENT, ALARM, HOT TERMINAL, MOISTURECLEAN VENT, NORMAL DISPLAY, TIGHT TERMINALS CCR INSPECTION SEQUENCE Look outsideVents, display, alarmsIsolateLocked out, proved deadOpen upSeals, dust, moistureTerminationsHeat marks, tightnessEarth, labelsStrap, nameplate, labelsRecordPhoto, circuit, action Do not open the cabinet until the CCR is isolated, locked out and proved dead. SCHEMATIC · CCR LAYOUTS AND CHECKLISTS DIFFER BETWEEN MAKES AND SITES · NOT TO SCALE
Figure 17. Two constant current regulator cabinets side by side.
AGL Visual Encyclopedia: CCR Inspection CCR Maintenance CCR Cooling System
Documentation

CCR Test Report Structure

A professional CCR test report should contain the following sections.

Equipment Identification

  • Airport & location
  • CCR number
  • Manufacturer & model
  • Serial number & rating

Electrical Test

  • Input voltage, frequency & current
  • Output current & voltage
  • Power & power factor where applicable

Brightness & Functional Test

  • Brightness-step results
  • Local & remote control
  • Monitoring, alarm & protection

Final Result: PASS / FAIL / CONDITIONAL ACCEPTANCE

Learn From Others

Common CCR Engineering Mistakes

Recognising these recurring mistakes early in a project is far cheaper than correcting them after installation.

01

Selecting Only by kW

Choosing the CCR by power rating alone, ignoring the actual circuit.

02

Ignoring Actual Circuit Load

Not establishing the real series-circuit loading.

03

Checking Voltage, Not Current

Overlooking the CCR's primary controlled parameter.

04

Replacing Without Testing the Field

Swapping the CCR before testing the field circuit.

05

Ignoring Transformer Compatibility

Not verifying isolation-transformer compatibility.

06

Assuming All LEDs Are Compatible

Treating LED fixture compatibility as automatic.

07

Ignoring Historical Data

Not reviewing historical CCR measurements and trends.

08

Skipping Remote Control Checks

Failing to verify remote control operation.

09

Ignoring Thermal Conditions

Overlooking ventilation and thermal management.

10

Stopping at Electrical Testing

Treating CCR testing as complete without system-level and photometric verification.

The Big Picture

The Complete CCR Engineering Chain

A CCR is not an isolated cabinet — it is the electrical control point of the entire series-circuit lighting system.

Airport Supply
Protection
CCR
Control
Current Regulation
Series Circuit
Isolation Transformers
Connectors
AGL Fixtures
Optical Output
Photometry
Aircraft Visual Guidance
Practical Model

CCR Performance Model

A practical way to organise CCR performance evaluation across six dimensions.

Electrical

Input → Regulation → Output

Control

Command → Brightness → Response

Protection

Fault → Detection → Protection

Monitoring

Condition → Measurement → Alarm/Status

System

CCR → Circuit → Fixture → Light

Verification

Current → Voltage → Function → Photometry

The Full Library

CCR Deep-Dive Knowledge Areas

The CCR knowledge library can be divided into eight areas.

Fundamentals

CCR principle, constant-current operation, series-circuit architecture.

Engineering

Selection, load calculation, circuit loading, output voltage, brightness control, compatibility.

Electrical

Input supply, output current, output voltage, power factor, efficiency, earthing.

Control

Local control, remote control, ALCMS integration, monitoring, protection.

Protection

Open circuit, short circuit, earth fault, overtemperature, input disturbances.

Testing

FAT, SAT, commissioning, periodic testing, functional testing.

Troubleshooting

Low/high/unstable current, high/low voltage, no output, alarms, communication failure.

Maintenance

Inspection, cleaning, thermal checks, electrical measurements, historical trending.

The Core Idea

The CCR Engineering Principle

A CCR is not merely a power source. It is the controlled electrical heart of an AGL series circuit. Its performance must therefore be evaluated through the complete chain:

Input Power → Regulation → Series Circuit → Transformer → Fixture → Optical Output

A CCR is truly performing correctly only when the electrical, control, protection, monitoring and system-level performance are all verified.

The Final Model

Select → Calculate → Install → Control → Measure → Monitor → Test → Verify → Maintain

Select & Calculate

Choose the correct CCR for the circuit and determine circuit load and operating requirements.

Install & Control

Connect the CCR correctly to the airport electrical and series-circuit systems, then verify local and remote brightness control.

Measure, Monitor & Test

Measure current, voltage and relevant electrical parameters; verify status, alarms, monitoring and protection functions.

Verify

Confirm complete circuit operation across control, protection and monitoring.

Measure Optically

Verify fixture/system performance through photometry where applicable.

Maintain

Trend performance over time and investigate deviations early.

CCR Engineering = Regulate → Control → Protect → Monitor → Test → Verify

Standards & References

CCR Standards Companion

The principal FAA equipment reference for CCRs is FAA AC 150/5345-10H, Specification for Constant Current Regulators and Regulator Monitors — currently identified by the FAA as Active, issued November 5, 2014.

AC 150/5345-10H

CCR & Regulator Monitor specification

ICAO Annex 14

Volume I, Aerodrome Design

L-824

Underground cable requirements

L-823

Plug/receptacle requirements

Related references may also include applicable FAA AC 150/5340 series circulars, isolation-transformer requirements, applicable IEC standards, applicable Indian Standards, DGCA requirements, airport-specific technical specifications, approved project drawings, manufacturer manuals and approved ITP/commissioning procedures. The exact acceptance criteria should always come from the current applicable standard, approved project specification, manufacturer documentation and system design — not generic values.

Constant Current Regulator India

For a constant current regulator in India, the airport's technical specification normally sets the requirement, referring to FAA AC 150/5345-10H or the equivalent IEC standard together with DGCA and AAI requirements. Confirm the exact standard, certification and test criteria with the project specification before selecting or accepting a CCR.

Test Yourself

Quick Knowledge Check

Q1. What is the primary controlled output parameter of a CCR?

A. Voltage
B. Current
C. Frequency
D. Power factor only

Q2. What is the current active FAA specification for Constant Current Regulators and Regulator Monitors?

A. AC 150/5340-30
B. AC 150/5345-42
C. AC 150/5345-10H
D. AC 150/5370-10

Q3. Why does an AGL series circuit use constant current rather than constant voltage?

A. Because circuit electrical characteristics change with load, cable, temperature and faults, and current must remain controlled
B. Because voltage sources are more expensive
C. Because fixtures cannot accept voltage variation of any kind
D. Because ICAO requires all lighting to run on DC

Q4. When troubleshooting a CCR issue, what is the recommended first step?

A. Replace the CCR immediately
B. Observe, measure and compare before isolating the fault
C. Shut down the entire airport electrical supply
D. Assume the field circuit is always at fault
Explore More

Explore Related AGL Engineering Topics

DESIGN

AGL Design & Electrical Engineering

Understand how CCRs are selected and incorporated into complete AGL electrical systems.

Open AGL Design Engineering →
CIRCUIT

AGL Cables & Connector Engineering

Understand the series-circuit path between CCRs, transformers and fixtures.

Open Cables & Connector Engineering →
INTERFACE

Isolation Transformer Engineering

Understand the electrical interface between the series circuit and individual fixtures.

Open Isolation Transformer Engineering →
VERIFICATION

AGL Testing & Inspection

Learn how CCR current, voltage, control and protection are verified.

Open AGL Testing & Inspection →
DIAGNOSIS

AGL Troubleshooting Engine

Diagnose low current, high current, earth faults, open circuits and unstable output.

Open the Troubleshooting Engine →
PERFORMANCE

AGL Photometry

Connect CCR electrical performance with actual optical system performance.

Open AGL Photometry →
APPLICATION

Runway Lighting Systems

Understand CCR application in runway circuits.

Open Runway Lighting →
APPLICATION

Taxiway Lighting Systems

Understand CCR application in taxiway circuits.

Open Taxiway Lighting →

Regulate. Control. Protect. Verify.

A CCR is not merely a power source — it is the controlled electrical heart of an AGL series circuit. Explore the complete AGL engineering knowledge base to see how it fits into the full picture.

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AGL Engineering Hub

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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 (CCR)?

A CCR is an electrical power-control device designed to maintain a controlled output current for an AGL series circuit. It sits at the beginning of the series circuit as the interface between the airport electrical supply, the series circuit, the isolation transformers and the individual light fixtures. It is a current-regulating system, not simply a power supply.

Q2Why does AGL use constant current?

Series circuits can contain many fixtures over long distances, and their electrical characteristics change with the number of fixtures, transformer characteristics, cable impedance and length, temperature, fixture condition and faults. A conventional constant-voltage supply would not give the same controlled current behaviour under these changes, so the CCR regulates series-circuit current instead.

Q3Is a CCR just a transformer that supplies the runway?

No. A CCR is a controlled current-regulating system whose function is to regulate output current despite changes in circuit conditions within its designed operating range. The internal technology varies by design, so it should not be assumed from the term CCR alone.

Q4What technologies are used in CCRs?

CCR technology has included saturable reactor types (older designs using magnetic saturation), ferroresonant types (magnetic components and resonance), static or electronic CCRs (semiconductor power electronics, control electronics and digital monitoring) and hybrid designs that combine magnetic and electronic technologies.

Q5What are L-828 and L-829, and which FAA specification covers CCRs?

In FAA terminology L-828 and L-829 are important CCR classifications, with the distinction primarily associated with regulator and monitoring or control functionality. The page states that the FAA currently lists AC 150/5345-10H as the active specification for Constant Current Regulators and Regulator Monitors. Equipment type and certification requirements should be checked against the current FAA specification and project requirements.

Q6How does a CCR control light brightness?

AGL intensity is controlled by changing the series-circuit current: higher current gives higher light output and lower current gives lower output. The actual current at each brightness step must come from the applicable CCR, lighting system and project requirements, and the current-to-intensity relationship is equipment-dependent.

Q7Why does CCR output voltage change with the circuit?

A CCR holds current, not voltage. As circuit resistance increases, for example with more fixtures, longer cable or ageing connections, the CCR raises its output voltage to hold current constant, within its designed operating limits.

Q8What happens if CCR output current drifts from its intended level?

If output is lower than intended, fixtures may appear dim, photometric performance may be reduced and a fault may exist in the regulator or circuit. If it is higher, fixture loading and equipment stress may increase, optical output may exceed its intended condition, and protection or monitoring functions may operate. CCR current verification is an essential part of AGL testing.

Q9What are the open-circuit, short-circuit and earth-fault conditions in a CCR circuit?

An open circuit breaks the current path, for example from a broken cable, disconnected connector or failed transformer, and can cause high output voltage, a fault indication or a regulator trip. A short circuit bypasses the load, for example through cable insulation failure or water ingress. An earth fault leaks current to ground. Each produces a different CCR response, and readings should be confirmed against the CCR manufacturer's documentation.

Q10Can an existing CCR be assumed compatible with every LED fixture?

No. LED fixtures changed the electrical behaviour and loading of many AGL systems. Check current waveform, control behaviour, minimum load, harmonics and power factor. The right question is whether the CCR is compatible with the complete AGL series-circuit load.

Q11How does a CCR work in airport lighting?

A CCR (constant current regulator) takes AC power and delivers a regulated current into a series loop of cable and isolation transformers. It senses its output current, compares it with the target for the selected brightness step, and adjusts its output voltage to hold the current constant whatever the load. Protection and monitoring functions detect open circuit, earth fault and similar conditions.

Q12What is airport lighting earth testing?

Airport lighting earth testing measures the resistance of the earth connections of the CCR installation and the associated equipment, so that fault current has a safe path and protective and surge devices work as intended. It is usually done alongside insulation (megger) testing of the series circuit.

Q13How is an airport lighting series circuit designed?

Design starts by listing the fixtures and loads on each circuit, then selecting the CCR rating with spare capacity, routing and sizing the cable, and splitting the lights into circuits by function and zone. Earthing and protection are specified, and the finished circuit is verified by insulation, continuity and current tests.

Q14What do CCR fault codes mean?

CCR fault codes are manufacturer-specific. They normally indicate conditions such as overcurrent, open circuit, earth fault, overtemperature or input abnormalities. Read the code from the display or control system, record the time and brightness step, and look it up in the manufacturer's manual before acting.

Q15What should I check when a CCR is not working at an airport?

Check the input supply, the local or remote selector, the control command, any protection trip and the output current. If an earth fault is suspected, do not repeatedly re-energise the circuit; isolate it, split the loop and insulation-test each section. Always isolate and lock out before touching the circuit.

Q16What is airport lighting insulation testing?

Airport lighting insulation testing measures the insulation resistance of cables, connectors and transformers, usually with a megger, to confirm they isolate the series circuit from earth. It is done at commissioning, periodically and after repairs, with the circuit isolated and locked out, and the results are trended over time.

Q17How to troubleshoot a constant current regulator?

Check the alarm or trip first, then supply voltage and output current. If current is wrong or zero, isolate and lock out the CCR and test the series circuit for open circuit, earth fault or low insulation. Only then suspect the regulator itself.

Q18How to maintain a CCR?

Clean the cabinet and ventilation, check terminals and earthing, verify output current at every brightness step, test protection and control, and record readings so changes over time show up. Follow the manufacturer's schedule.

Field Insight

Engineering & Expert Notes

RS
By Rahul Sharma
Airfield Ground Lighting Specialist
The CCR Controls Current, and Voltage Follows the Load
Principle

Understanding this explains why open circuits are dangerous and why output voltage changes with the circuit.

Verify Every Brightness Step
Output

Measure current at each step during commissioning and compare with the expected values.

Cooling and Environment Affect Reliability
Environment

Check ventilation, filters and room temperature. Heat is a common cause of premature failure.

Know How the Protection Behaves
Protection

Understand open-circuit and overcurrent protection, and test only under the approved procedure.

Check Loading Against the Rating
Loading

Calculate and record load as circuits are modified. Overloaded CCRs run hot and operate poorly.

Use Fault Codes Carefully
Diagnostics

Codes point to a likely area, not always the root cause. Confirm with measurement.

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