BASIC AGL ELECTRICAL CHAIN
POWER SUPPLY
│
▼
CCR
│
▼
PRIMARY CABLE
│
▼
PRIMARY CONNECTOR
│
▼
ISOLATING TRANSFORMER
│
▼
SECONDARY CONNECTOR
│
▼
AGL LIGHT
This simplified diagram is one of the most important diagrams for an AGL student to understand. It is drawn as a straight chain for clarity: in a real circuit the primary cable runs through every isolating transformer in turn and returns to the CCR to complete a loop (see section 2).
CONSTANT CURRENT REGULATOR (CCR)
CCR = Constant Current Regulator. It supplies controlled current to the AGL series circuit. FAA currently lists AC 150/5345-10H as the specification for constant-current regulators and regulator monitors used with airport lighting circuits.
Basic function
- Supplies the series circuit
- Controls circuit current
- Provides different lighting intensity levels in applicable systems (typically 3 or 5 brightness steps)
- Interfaces with airport lighting control arrangements
Typical FAA values (check the applicable specification)
- Class 1 = 6.6 A output; Class 2 = 20 A output (for specific applications)
- Style 1 (3 brightness steps), Class 1: 4.8 / 5.5 / 6.6 A
- Style 2 (5 brightness steps), Class 1: 2.8 / 3.4 / 4.1 / 5.2 / 6.6 A
- Designation: L-828 = regulator without monitoring; L-829 = regulator with monitoring
More detail: Study Note 07: Constant Current Regulators.
Why is a CCR used in AGL?
Because the series-circuit lighting system is designed to operate with controlled constant current, so every light in the circuit receives the same current.
What are the typical FAA CCR output currents?
Maximum 6.6 A. A 3-step CCR gives 4.8, 5.5 and 6.6 A; a 5-step CCR gives 2.8, 3.4, 4.1, 5.2 and 6.6 A.
SERIES CIRCUIT
In a series AGL circuit, the lighting units are connected as part of a continuous circuit supplied by the CCR. A simplified circuit:
CCR out ─► [Transformer 1] ─► [Transformer 2] ─► [Transformer 3] ─► … ─► [Transformer N] ─┐ ▲ │ │ │ │ │ │ Light 1 Light 2 Light 3 Light N │ │ │ └─────────────────────── return to CCR: the loop is continuous ───────────────────────┘
The circuit is a single continuous loop: the same current leaves the CCR, passes through every isolating transformer primary in turn and returns to the CCR. It is not a set of branches. The actual installation uses primary cabling and associated connectors to form the loop.
Why a series circuit?
- The same current flows through every light, so brightness stays uniform regardless of cable length or the number of lights
- One CCR controls the intensity of the whole circuit
- A failed lamp does not open the loop, because each light is fed through an isolating transformer
Why is a series circuit used for airfield lighting?
The same current flows through every light, so brightness stays uniform regardless of cable length, and the circuit is controlled by one CCR.
Why must an energised series circuit never be opened?
The CCR tries to keep the current constant, so opening the loop can produce a dangerously high voltage. Isolate the CCR and follow lockout and permit-to-work procedure first.
ISOLATING TRANSFORMER
An AGL isolating transformer provides electrical isolation between the primary series circuit and the individual light fixture. FAA AC 150/5345-47C specifically covers series-to-series isolation transformers for airport lighting systems.
Why is it important?
- Electrically isolates the fixture from the primary series circuit
- Transfers power to the secondary side
- Allows individual fixtures to connect to the series circuit
- Forms a key interface between the primary circuit and light fixture
- Keeps the primary loop closed if a lamp fails, so one dead lamp does not put out the whole circuit
Designations and ratings
- L-830 = 60 Hz series; L-831 = 50 Hz series (check which applies to your supply frequency)
- Typical series-circuit rating: 6.6 A primary, with different wattage sizes for different fixtures
More detail: Study Note 08: AGL Isolating Transformers.
Which FAA isolating transformer designation is for 50 Hz systems?
L-831 is the 50 Hz series; L-830 is the 60 Hz series. Check the project specification for the applicable frequency.
PRIMARY CABLE
The primary cable forms part of the high-voltage series circuit. FAA's current advisory circular listing identifies AC 150/5345-7F as the specification for L-824 underground electrical cable for airport lighting circuits. L-824 cable is available in 5,000 V and 600 V ratings; series-circuit (primary) cable is the 5,000 V type. The primary circuit can be studied as:
More detail: Study Note 09: AGL Primary & Secondary Circuits.
PRIMARY CONNECTOR
Primary connectors join lengths of series-circuit cable and connect the cable to the isolating transformer primary and other equipment. In FAA systems these are normally L-823 connectors (see the next section).
L-823 PLUG & RECEPTACLE
L-823 connectors are used in airport lighting systems for connections involving underground power cables, isolation transformer leads and light fixture leads. AC 150/5345-26E is the current FAA specification for L-823 plug and receptacle cable connectors. L-823 covers both the primary (series-circuit) connectors and the secondary (fixture-lead) connectors.
Exam point
- L-823 = Airport Lighting Cable Connector
More detail: Study Note 10: L-823 Connectors.
SECONDARY CONNECTION
The transformer secondary side supplies the individual lighting fixture through the secondary connection. The secondary side is a low-voltage circuit serving one fixture, unlike the primary series loop. A simplified arrangement:
PRIMARY SIDE
│
│
CCR ───── Primary Cable ───── Transformer
│
│
Secondary Cable
│
▼
AGL FixtureHOW AN AGL CIRCUIT WORKS
Suppose a runway contains many lights. Instead of supplying every fixture independently from a conventional low-voltage distribution board, the AGL system can use a series circuit supplied by a CCR.
- The CCR controls the circuit current
- Each fixture is connected through an isolating transformer
- The fixture receives the appropriate secondary-side supply
- The series circuit is isolated from earth by design, so insulation resistance to earth is an important health indicator
This makes the relationship between CCR + Cable + Transformer + Connector + Fixture fundamental to AGL troubleshooting.
SECONDARY POWER & SWITCH-OVER TIME
The power supply at the top of the electrical chain must be reliable. ICAO Annex 14, Volume I, Chapter 8 requires a secondary power supply for precision approach runways (and, with limits, for non-precision runways), arranged to connect automatically if the primary source fails. The key figure is the maximum switch-over time: how long the light output may be interrupted during the change.
| Runway type | Maximum switch-over time |
|---|---|
| Non-precision approach | 15 seconds for the listed lighting aids |
| Precision approach CAT I | 15 seconds for the listed lighting aids |
| Precision approach CAT II/III | 1 second for key lights (such as the inner 300 m of the approach lighting, runway centreline, touchdown zone and stop bars); 15 seconds for the other listed lights |
What switch-over times does ICAO Annex 14 set for secondary power?
The maximum is 15 s for most lights on CAT I runways. For CAT II/III, key lights such as the inner 300 m of the approach lighting, runway centreline, touchdown zone and stop bars need 1 s. Confirm in Annex 14 Table 8-1.
AGL FAULT-FINDING LOGIC
When an AGL fault occurs, avoid immediately replacing the light. Ask:
- Is the CCR operating correctly?
- Is the series circuit energised?
- Is the primary circuit continuous, and is its insulation resistance to earth acceptable?
- Are the connectors satisfactory?
- Is the isolating transformer healthy?
- Is the secondary connection satisfactory?
- Is the light fixture working?
This creates a logical troubleshooting sequence.
Example fault: one runway light not operating
Possible causes
- Fixture fault
- Secondary connector problem
- Transformer fault
- Primary connector problem
- Local cable issue
Do not assume the lamp or LED module is automatically the fault.
Example fault: several lights in a series circuit not operating
Consider
- CCR output
- Primary circuit
- Cable continuity
- Connector condition
- Multiple component failures
The more fixtures affected, the more important it becomes to investigate the common part of the system.
Whole circuit or part of it?
- Whole circuit dark: suspect the CCR (including its protection) or an open primary loop
- Only some lights out: the loop is intact, so the fault is local to those fixtures, transformers or connectors
If the whole circuit is dark, where should you look first?
At the CCR (including its protection) and the primary loop for an open circuit. If only some lights are out, the loop is intact and the fault is local to those fixtures.
AGL ELECTRICAL REVISION TABLE
| Component | Main function |
|---|---|
| CCR | Controls series-circuit current |
| Primary Cable | Carries the primary series-circuit current |
| Primary Connector | Connects primary circuit components |
| Isolating Transformer | Provides isolation and transfers power to fixture |
| Secondary Connector | Connects transformer secondary to fixture |
| Light Fixture | Produces the visual light output |
| L-823 | Standardised airport lighting connector specification in FAA system |
| Secondary power | Automatic back-up supply; switch-over 15 s, or 1 s for key CAT II/III lights (ICAO Annex 14) |
FAA's current airport-lighting advisory-circular catalogue separately identifies specifications for CCRs, L-823 connectors, isolation transformers and L-824 airport-lighting cable.
| FAA advisory circular | Covers |
|---|---|
| AC 150/5345-10H | Constant-current regulators and regulator monitors |
| AC 150/5345-47C | Series-to-series isolation transformers |
| AC 150/5345-7F | L-824 underground electrical cable |
| AC 150/5345-26E | L-823 plug and receptacle cable connectors |
Key points for exams
- CCR = Constant Current Regulator
- AGL commonly uses series circuits
- Transformer = isolation between primary series circuit and fixture
- L-823 = Airport lighting connector specification
- L-824 = Airport lighting underground cable specification in the FAA framework
- L-831 = 50 Hz isolating transformer series (L-830 = 60 Hz)
- CAT I switch-over 15 s; CAT II/III key lights 1 s
- Never open an energised series circuit
- Always understand the complete circuit before troubleshooting
ENGINEERING & EXPERT NOTES
Constant Current Changes How You Think About Faults
PrincipleOpen circuits, shorts and earth faults behave differently from a constant-voltage system. Learn the symptoms for each.
Verify Switch-Over by Test, Not by Datasheet
Secondary PowerMeasure the actual interruption on your equipment and check it against the applicable requirement.
Keep Drawings Aligned With the Field
RecordsFault finding is only as good as the drawings. Update them whenever circuits change.
Isolate, Discharge and Prove Dead
SafetyInsulation tests and series circuits both leave hazards. Follow the approved procedure each time.
REFERENCES & FURTHER READING
These notes are a study aid. Verify details against the primary sources below.
| # | Source | Use it for |
|---|---|---|
| 1 | ICAO Annex 14, Volume I – Aerodrome Design and Operations | Chapter 8 (Electrical Systems): secondary power supply and switch-over times (Table 8-1), light intensity control and monitoring. |
| 2 | ICAO Doc 9157 – Aerodrome Design Manual | Part 5 (Electrical Systems): series circuits, CCRs, isolating transformers and cabling guidance. |
| 3 | FAA AC 150/5340-30J – Design and Installation Details for Airport Visual Aids | Installation of series circuits, CCRs, cables, connectors, light bases, grounding and vaults. |
| 4 | FAA AC 150/5340-26C – Maintenance of Airport Visual Aid Facilities | Safety procedures for series circuits and preventive maintenance of CCRs and cabling. |
| 5 | FAA AC 150/5345-10 – Specification for Constant Current Regulators and Regulator Monitors | CCR specification (the notes cite the -10H edition). |
| 6 | FAA AC 150/5345-47 – Specification for Series to Series Isolation Transformers for Airport Lighting Systems | Isolation transformer specification (the notes cite the -47C edition). |
| 7 | FAA AC 150/5345-7 – Specification for L-824 Underground Electrical Cable for Airport Lighting Circuits | L-824 primary cable specification (the notes cite the -7F edition). |
| 8 | FAA AC 150/5345-26 – Specification for L-823 Plug and Receptacle, Cable Connectors | L-823 connector specification (the notes cite the -26E edition). |
| 9 | FAA AC 150/5345-42 – Specification for Airport Light Bases, Transformer Housings, Junction Boxes and Accessories | Light base and transformer housing specification. Use the current edition. |
| 10 | NFPA 70 – National Electrical Code (NEC) | Wiring and grounding practice referenced by the FAA advisory circulars. |
Read the Notes. Close the Gaps. Build AGL Expertise.
Study notes give you the concepts and the exam logic — Precision AGL Academy is where they connect into real technical capability.
Learn how AGL fundamentals, systems, testing, photometry, maintenance and troubleshooting connect through structured technical training, well beyond what a set of notes can cover.
Study smarter. Train deeper. Build technical capability.
Build structured knowledge in: