The Guide to AGL Isolating Transformers in the Airfield Lighting Series Circuit
An AGL isolating transformer is a critical interface between the airport series circuit and an individual airfield lighting fixture. It allows individual lighting loads to be connected to a constant-current series circuit while providing electrical isolation between the primary series circuit and the fixture's secondary circuit. Although physically small compared with a CCR or a lighting fixture, it is one of the most important components in the complete AGL circuit.
What Is an AGL Isolating Transformer?
An AGL isolating transformer is a transformer specifically used within an airfield lighting series circuit to electrically isolate an individual lighting load from the primary series circuit.
It is normally installed between the primary series-circuit cable and the individual fixture, and its fundamental functions are electrical isolation, energy transfer, providing the interface between primary and secondary circuits, matching the lighting fixture to the series-circuit architecture, and supporting reliable operation of each individual AGL fixture.
Electrical Isolation
Provides galvanic separation between the primary series circuit and the secondary fixture circuit.
Energy Transfer
Transfers electrical power from the series circuit to the individual fixture it supplies.
Circuit Architecture
Lets many fixtures form part of one common series circuit without joining their secondary circuits together.
The series loop feeds the primary; the secondary powers the lamp through magnetic coupling only.
AGL Visual Encyclopedia: Isolation transformer principle Transformer circuit position Electrical isolation
Why Isolating Transformers Are Used
AGL systems commonly use a constant-current series circuit. Instead of connecting every light fixture directly across a common voltage supply, individual fixtures are connected through isolation transformers — allowing multiple lighting units to operate as part of the same series circuit while maintaining electrical isolation at each individual load interface.
The CCR regulates the series-circuit current, each isolation transformer transfers power from the primary circuit to its associated fixture, and the fixture converts that electrical energy into light. The isolation transformer's job is to interface the individual load — not to regulate the circuit itself.
Primary Side vs Secondary Side
The transformer has two electrically isolated sides, each serving a distinct part of the circuit.
Primary Side
Connected to the CCR through the series-circuit cable. The primary side operates within the high-voltage series-circuit environment.
- CCR
- Series Circuit Cable
- Primary Connector
Secondary Side
Connected to the AGL fixture. The secondary side supplies the individual lighting load according to the transformer's design.
- Secondary Connector
- AGL Fixture
There is no direct wire between the primary and secondary windings — energy crosses the core magnetically, which is exactly what protects the fixture side from the series-circuit voltage
Why the Transformer Must Be Treated as an AGL Component
An ordinary electrical transformer should not automatically be substituted for an AGL isolating transformer. AGL transformers are selected for the specific electrical and environmental conditions of airport series circuits.
Transformer Ratings & Selection
One of the most important selection parameters is transformer power rating. Common ratings encountered in practical AGL systems include:
The required rating depends on the connected fixture/load and applicable design requirements. A transformer should not be selected simply because its rating is higher. The correct principle is:
A common engineering mistake is selecting the transformer only from fixture wattage. The complete system should be evaluated — fixture requirement, secondary electrical requirement, transformer rating, primary series-circuit compatibility and CCR compatibility all have to line up. For many AGL applications a nominal series-circuit current of 6.6 A is commonly encountered, but the actual operating current depends on the specific system and design, so selection must always be based on the applicable equipment specification and project design rather than one assumed universal current.
Fixture Side
- Fixture type
- Fixture power
- Fixture compatibility
Transformer Side
- Required rating
- Secondary requirements
- Insulation requirements
Circuit & Project Side
- Primary circuit requirements
- Installation environment
- Connector & cable configuration
- Standards & project specification
Loading of 45 W, 65 W and 100 W class transformers feeding a 45 W fixture.
AGL Visual Encyclopedia: Transformer sizing Transformer nameplate Transformer wattage ratings Transformer selection
Transformer Efficiency Estimator
The fundamental relationship is P ≈ V × I. For an ideal transformer, primary power ≈ secondary power; in practical operation, primary power is greater than secondary power because of copper losses, core losses, dielectric losses and other design-dependent losses. Adjust the values to see how losses affect efficiency.
This is an illustrative estimator, not a design or test tool. Real transformer efficiency, rating and losses must be taken from manufacturer data and verified by the applicable acceptance and test procedures — never assume secondary power can exceed primary power.
Construction, Insulation & Sealing
An AGL isolating transformer generally contains a magnetic core, primary winding, secondary winding, insulation system, housing/enclosure, leads or connectors, a sealing system and identification markings. The exact construction varies according to manufacturer and transformer design.
Insulation System
Electrical isolation depends on the integrity of the insulation system — winding insulation, inter-winding insulation, lead insulation, external insulation, sealing, moisture resistance and dielectric strength. Deterioration can eventually lead to leakage → earth fault → circuit instability → transformer failure.
Sealing
AGL transformers are installed in harsh outdoor environments — water, moisture, dust, mud, chemicals, temperature variation and mechanical stress. A properly designed and sealed transformer protects its internal electrical system from these conditions.
Water Ingress
One of the most important causes of field problems. Entry points include damaged housing, the cable/lead interface, the connector interface, seal deterioration, mechanical damage and incorrect installation — leading to insulation degradation, corrosion, leakage current, earth fault and reduced life.
Most field failures start at one of a small number of entry points — the housing, the cable/lead interface, the connector, or a degraded seal
Cutaway: housing, potting, insulation, windings and core.
AGL Visual Encyclopedia: Transformer construction Transformer housing Insulation system Sealing system
Primary & Secondary Connectors
The transformer is not an isolated component — it interfaces with a primary connector and a secondary connector, and connector compatibility must be verified before installation.
A connector that appears physically connected may still have an electrical problem. Incorrect mating can cause high resistance, intermittent operation, heating, voltage drop, flickering, fixture failure and water ingress. Therefore: Connected ≠ Correctly Connected.
Plug-in unit with moulded connectors compared with a field-jointed unit.
AGL Visual Encyclopedia: Plug-in isolation transformers Primary connector Secondary connector Connector sealing
LED & Lamp Fixture Compatibility
LED Fixtures
LED AGL fixtures may have different electrical characteristics from traditional lamp-based fixtures. Never assume a transformer designed for one fixture type is automatically suitable for another.
- Transformer rating
- Fixture input characteristics
- Secondary voltage & current behaviour
- Power factor
- Minimum loading
- Manufacturer compatibility requirements
Traditional Lamp Fixtures
Also require correct transformer selection. An incorrectly rated transformer can cause low lamp output, excessive electrical stress, premature lamp failure, transformer overheating and incorrect circuit loading.
- Lamp wattage
- Transformer rating
- Secondary requirements
- Lamp operating characteristics
- Applicable fixture specification
Installation & Locations
Installation should follow the approved design and manufacturer's instructions, verifying correct location, rating, identification, connections, cable routing and mechanical/environmental protection. Depending on the AGL system, transformers may be installed in transformer pits, in light bases, adjacent to fixtures, underground, within approved enclosures, or in other project-approved locations.
Location & Orientation
Correct transformer location, orientation where applicable, rating and identification, verified against the approved design before energizing.
Cable Routing
Routing should prevent excessive mechanical stress, sharp bending, connector damage, water accumulation, abrasion and improper cable tension — the transformer should never carry unnecessary mechanical load on its leads or connectors.
Identification
Manufacturer, model, rating, serial/batch number, primary/secondary rating and certification marking — important for installation, inspection, testing, maintenance, replacement and traceability.
Section through a pavement pit and the six installation checks.
AGL Visual Encyclopedia: Transformer-pit installation Transformer placement Transformer pit safety Buried and elevated transformers
Inspection & Electrical Testing
Testing should be performed using appropriate calibrated instruments and approved procedures. Continuity checks the electrical path, insulation resistance evaluates insulation condition, and winding, ratio/output and dielectric/withstand tests are used where specified — never apply generic test voltages without confirming the applicable requirement.
| Test | Purpose |
|---|---|
| Continuity | Checks the electrical path — identifies open winding, broken lead, poor connection or connector failure. Continuity alone does not prove the transformer is healthy: it can pass continuity and still have insulation failure, shorted turns or moisture ingress. |
| Insulation Resistance | Detects moisture, insulation degradation, contamination and winding or cable insulation problems, using the instrument, test voltage and procedure specified for the equipment. |
| Winding Tests | Used where specified by the applicable test procedure. |
| Ratio / Output Verification | Used where required by the transformer specification or test procedure. |
| Dielectric / Withstand | Performed according to the applicable standard and manufacturer's procedure. |
An insulation tester between the loop conductor and earth, with the CCR locked out.
AGL Visual Encyclopedia: Insulation-resistance testing Transformer testing Transformer inspection Insulation resistance
Common Field Failure Modes
Ten named failure modes recur across field experience, each with its own typical cause:
| Failure Mode | Possible Cause |
|---|---|
| Open winding | Internal winding failure |
| Insulation breakdown | Age, moisture, electrical stress |
| Water ingress | Seal/housing problem |
| Overheating | Overload, incorrect application |
| Connector failure | Poor mating, damage |
| Lead damage | Mechanical stress |
| Corrosion | Environmental exposure |
| Reduced output | Internal deterioration or incorrect loading |
| Earth fault | Insulation failure |
| Intermittent operation | Connection or insulation problem |
Click a failure mode below to see the typical causes an engineer should check before replacing a transformer.
Transformer Overheating
Possible Causes
- Overloading
- Incorrect transformer rating
- Excessive ambient temperature
- Poor installation
- Internal winding losses
- Fixture incompatibility
Earth Fault
Possible Causes
- Primary or secondary insulation breakdown
- Water ingress
- Damaged leads
- Internal winding insulation failure
- Connector contamination
Open Circuit
Possible Causes
- Broken winding
- Damaged lead
- Loose connector
- Internal failure
- Installation damage
Repeated Multiple Failures
Possible Causes
- Incorrect CCR output
- Excessive circuit current
- Wrong transformer rating
- Incompatible fixtures
- Cable or connector problems
Never conclude "the transformer is faulty because the light is OFF." A useful field sequence works backward from the fixture: Fixture → Secondary Connector → Transformer → Primary Connector → Series Cable → CCR. This prevents unnecessary replacement of healthy components.
Start at the dark fixture and check each stage moving toward the CCR — replacing the transformer first, before the stages on either side of it are checked, is the most common wasted step
Same series current in three states: loaded, secondary open, and core saturated.
AGL Visual Encyclopedia: Open-secondary and core saturation Transformer failure modes Film cutout operation Secondary shorting overvoltage
Transformer Troubleshooting
Two common symptoms and the checks an engineer should work through before condemning a transformer.
One Light Completely Dark
- Fixture
- Secondary connector
- Transformer secondary
- Transformer primary
- Primary connector
- Series cable
Light Flickering
- Connector mating
- Secondary connection
- Transformer condition
- Cable connection
- Fixture
- CCR current stability
An individual dark fixture can be caused by lamp/LED failure, fixture wiring, the secondary connector, the transformer, the primary connector, the cable, the CCR, or a wider circuit fault — never conclude it's the transformer on symptom alone.
Troubleshooting Philosophy
SYMPTOM
INSPECT
MEASURE
ISOLATE
CONFIRM
REPLACE
RE-TEST
Five checks marked on a potted isolation transformer.
AGL Visual Encyclopedia: Transformer troubleshooting Transformer failure Transformer continuity Connector troubleshooting
The Transformer's Relationships in the Wider System
Transformer & CCR
The CCR controls the primary series-circuit current; the transformer receives that current and transfers power to the fixture. If the CCR current is incorrect, the fixture may not operate at its intended condition even when the transformer itself is healthy.
Transformer & Photometry
The transformer itself does not determine the complete optical performance of a fixture — photometric performance depends on the complete chain from CCR through the series circuit, transformer, fixture and optical system to light output. Photometric verification may be required after transformer replacement.
Transformer Compatibility Matrix
A practical compatibility check should consider every parameter below before a transformer is accepted for installation.
| Parameter | Requirement |
|---|---|
| CCR | Compatible |
| Primary cable | Compatible |
| Primary connector | Compatible |
| Transformer rating | Correct |
| Secondary output | Correct |
| Secondary connector | Compatible |
| Fixture | Compatible |
| Installation | Approved |
| Environment | Suitable |
| Standards | Compliant |
Transformer Replacement & Commissioning
Before replacing a transformer: identify the failed unit, confirm the failure through testing, verify replacement rating and primary/secondary/connector compatibility, install correctly, test, energize, verify fixture operation, and record the replacement.
IDENTIFY
Confirm the failed component through testing, not assumption.
VERIFY
Rating, primary, secondary and connector compatibility.
INSTALL
Correct location, connections, sealing and cable routing.
TEST
Continuity, insulation and applicable acceptance tests.
ENERGIZE & VERIFY
Confirm secondary output and fixture operation.
RECORD
Log the replacement and update traceability records.
Transformer Reliability Model
A high-quality transformer can still fail prematurely if installed or loaded incorrectly. Reliability depends on the complete chain, not the component alone:
Common Engineering Mistakes
Wrong Component Class
Using an ordinary transformer instead of an approved/suitable AGL isolating transformer.
Wattage-Only Selection
Selecting the transformer only by wattage, ignoring the complete system evaluation.
Ignoring Compatibility
Ignoring fixture compatibility and CCR compatibility during selection.
Connector Shortcuts
Using incorrect connectors or accepting poor connector mating.
Allowing Water Ingress
Failing to protect leads, connectors and housings from moisture exposure.
Replace-First Habit
Replacing the transformer without testing the circuit, or assuming continuity proves health.
Mechanical Overstress
Applying excessive mechanical stress to transformer leads during installation.
Poor Traceability
Ignoring repeated failure patterns, or failing to record transformer ID and test history.
Series Lighting Transformer: Working Principle, Types, Functions & Components
How the series lighting transformer works inside the airfield lighting series circuit, and what it is made of.
Series lighting transformer
A series lighting transformer is the device that lets one lighting load sit on a constant-current series loop without breaking the loop. The primary winding carries the circuit current, and the secondary feeds a single fixture. Because every transformer in the airfield lighting series circuit shares the same current, the brightness setting is controlled at the CCR rather than at each fixture.
Airfield lighting isolation transformer working principle
The primary winding is connected in series with the circuit, so the circuit current magnetises the core and induces a secondary current in the lamp or LED driver. Isolation means the fixture is not electrically tied to the high-voltage primary loop. If a lamp fails and the secondary opens, the transformer design limits the effect so the rest of the circuit keeps running. Core design and the way a transformer behaves with an open or lightly loaded secondary should be confirmed against the manufacturer's datasheet.
Airfield lighting isolation transformer types
Types are usually separated by rated load, by the fixture they serve and by how they are installed. Common groupings are different wattage ratings, units for elevated and in-pavement fixtures, and units with different lead and connector arrangements. Series-to-series isolating transformers are the standard type in AGL, but the exact classification follows the specification used for the project.
Airfield lighting isolation transformer functions
The main functions are isolating the fixture from the primary circuit, transferring energy to the load, matching circuit current to the fixture's needs, and keeping the series circuit healthy when a load fails. A well-built transformer also protects maintenance staff by keeping dangerous primary voltage away from the fixture side.
Airfield lighting isolation transformer components
The main components are the magnetic core, primary and secondary windings, the insulation system, the housing or moulded body, the primary and secondary leads or connectors, and the sealing that keeps moisture out. The quality of the insulation and sealing largely decides field life. See the Construction, Insulation & Sealing section above for more detail.
Specification, Design, Requirements, Standards & Selection Guide
What an airfield lighting isolation transformer must meet, and how to choose and justify one.
Airfield lighting isolation transformer specification
A specification should state the circuit current, rated load, primary and secondary connection type, insulation and sealing requirements, environmental limits, marking and the standard the unit is tested to. Keeping the specification tied to the fixture and CCR it will work with avoids mismatches discovered during commissioning.
Airfield lighting isolation transformer requirements
Requirements come from three directions: the aerodrome regulator, the standard the project follows, and the project's own design basis. In practice they cover electrical performance, insulation integrity, mechanical robustness, connector compatibility, sealing and traceability. Requirements should be checked against the editions of the standards your project uses.
Airfield lighting isolation transformer design
Design covers the core and winding arrangement, how the unit behaves with an open or partly loaded secondary, insulation system, thermal behaviour, lead and connector arrangement and housing. At circuit level, designers also account for the combined effect of all transformers on the series loop and the CCR.
Airfield lighting isolation transformer standards
Commonly referenced documents include FAA advisory circular AC 150/5345-47 for series-to-series isolation transformers, IEC 61823 for AGL series transformers, and ICAO Annex 14 and the ICAO Aerodrome Design Manual for the wider lighting system. Please confirm the exact documents and editions that apply to your project and regulator, including any DGCA requirements.
Airfield lighting isolation transformer selection guide
Select in this order: the fixture and its load, the circuit current and CCR, the connector type, the installation location, and the standard the unit must be approved to. Selecting on wattage alone is a common mistake. See Transformer Ratings & Selection and the Transformer Compatibility Matrix above.
Airfield lighting isolation transformer technical guide
As a technical guide, think of the transformer as the interface between three things: the primary series circuit, the fixture, and the maintenance process. Each section on this page covers one part of that interface, from construction and connectors to testing and replacement.
Installation, Commissioning & AGL Transformer Testing
Getting the transformer into service correctly and proving it works.
Airfield lighting transformer installation
Installation means placing the transformer at the right location, making the primary and secondary connections correctly, protecting the leads from mechanical stress and keeping connectors clean, dry and fully mated. Follow the manufacturer's instructions and the project installation specification, and record the transformer identification against the fixture location.
Airfield lighting isolation transformer installation
For an isolation transformer specifically, check before installing that the rating suits the fixture, that the housing and leads are undamaged, and that the connector type matches. After installation, check connector seating and sealing before backfilling or closing the fixture base.
AGL transformer testing
AGL transformer testing normally combines visual inspection, continuity checks and insulation resistance testing, followed by an operational check with the circuit energised under the correct safety procedure. Test values and limits come from the manufacturer and project specification, so I have not stated figures here. Results should always be recorded. See Inspection & Electrical Testing and the Transformer Test Record above.
Airfield lighting isolation transformer testing procedure
A typical procedure runs: isolate and secure the circuit, inspect the transformer and connectors, perform insulation and continuity checks, reconnect, energise under controlled conditions, confirm fixture operation and record the results. Always follow your site's lock-out and permit-to-work procedure.
Airfield lighting isolation transformer commissioning
Commissioning confirms that every installed transformer and its fixture work correctly on the energised circuit. It normally includes verifying identification, connector condition, insulation test records, fixture output at the commissioning brightness steps and circuit behaviour. Any deviation is recorded and closed before handover. See Transformer Replacement & Commissioning above.
Maintenance, Preventive Maintenance & Troubleshooting
Keeping the transformer in service, and finding faults efficiently when it is not.
Airfield lighting isolation transformer maintenance
Maintenance covers scheduled inspection, connector checks, insulation testing and replacement of damaged units. Most field problems begin at connectors and seals, so these should be the first things checked.
Airfield lighting isolation transformer preventive maintenance
Preventive maintenance finds problems before they cause outages. Typical activities are periodic insulation resistance trending, visual inspection of housings and leads, checking for water ingress, and keeping records so repeated failures in one area become visible. The inspection interval should follow your maintenance plan and the aerodrome's requirements.
Airfield lighting isolation transformer troubleshooting
Troubleshoot from the symptom: one fixture out, a group out, or a circuit fault. Test before replacing, because continuity alone does not prove a transformer is healthy. Check connectors and leads first, then insulation, then the transformer and fixture individually. See Common Field Failure Modes and Transformer Troubleshooting above.
Transformer Inspection Checklist
Check off items as you go — each phase tracks its own completion.
Physical
Leads & Connectors
Electrical
Installation
Transformer Test Record
A practical record sheet used to log each transformer's test result.
| Parameter | Result |
|---|---|
| Transformer ID | ___ |
| Manufacturer | ___ |
| Model | ___ |
| Rating | ___ W |
| Primary Rating | ___ |
| Secondary Rating | ___ |
| Continuity | PASS/FAIL |
| Insulation Resistance | ___ |
| Secondary Output | ___ |
| Connector Condition | PASS/FAIL |
| Physical Condition | PASS/FAIL |
| Final Result | PASS/FAIL |
Transformer Selection Decision
Before installing an AGL isolating transformer, work through these questions — check them off as you go.
Electrical & Fixture Fit
Compliance & Documentation
Complete AGL Transformer Engineering Chain
An AGL isolating transformer is the electrical interface between the series circuit and the individual lighting fixture: CCR → Cable → Connector → Transformer → Connector → Fixture. Correct performance depends on correct selection, correct installation, correct connection, correct loading and correct testing — together, not in isolation.
AGL Transformer Performance Model
Electrical
Primary → Isolation → Secondary
Mechanical
Housing → Leads → Connectors → Mounting
Environmental
Sealing → Moisture Protection → Temperature → Durability
Compatibility
CCR → Cable → Transformer → Fixture
Verification
Inspect → Test → Energize → Verify
Final AGL Isolating Transformer Model
AGL Isolating Transformer = Isolation + Energy Transfer + Load Interface + Reliability. The transformer may be a small component physically, but it is a critical link in the complete AGL electrical chain.
Standards & References
The exact requirements for an AGL isolating transformer depend on the applicable equipment specification, airport design and project requirements.
Volume I aerodrome design and operations
Applicable airfield lighting circulars
Applicable connector & cable requirements
Applicable IEC standards & Indian Standards
Quick Knowledge Check
Q1. What is the fundamental function of an AGL isolating transformer?
Q2. What is the correct principle for selecting a transformer rating?
Q3. Why is "continuity PASS" not the same as "transformer PASS"?
The AGL Transformer Knowledge Hub
AGL Design & Electrical Engineering
Understand transformer selection within the complete series-circuit design.
Open AGL Design →AGL Cables & Connector Engineering
Understand primary and secondary cable and connector interfaces.
Open Cables & Connectors →Constant Current Regulators Deep Dive
Understand the CCR that supplies the series circuit.
Open CCR Deep Dive →AGL Testing & Inspection
Learn how transformers are inspected and electrically tested.
Open Testing & Inspection →AGL Troubleshooting Engine
Diagnose transformer, connector, cable and fixture failures.
Open Troubleshooting Engine →AGL Installation & Commissioning
Understand field installation and commissioning procedures.
Open Installation & Commissioning →AGL Photometry
Understand how electrical performance ultimately affects optical performance.
Open AGL Photometry →Small Component. Critical Link.
The transformer may be physically small, but it is a critical link in the complete AGL electrical chain — isolation, energy transfer, load interface and reliability, together.
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Frequently Asked Questions
Q1What is an AGL isolating transformer?
An AGL isolating transformer is a transformer used in an airfield lighting series circuit to electrically isolate an individual lighting load from the primary series circuit. It is normally installed between the primary series-circuit cable and the individual fixture, providing electrical isolation, energy transfer and the interface between primary and secondary circuits.
Q2Why are isolating transformers used in AGL series circuits?
AGL systems commonly use a constant-current series circuit. Instead of connecting every fixture directly across a common voltage supply, fixtures are connected through isolation transformers, so many lighting units can operate in the same series circuit while each load stays electrically isolated. The CCR regulates the circuit current; the transformer only interfaces the individual load.
Q3What is the difference between the primary and secondary side of the transformer?
The primary side connects to the CCR through the series-circuit cable and primary connector, within the high-voltage series-circuit environment. The secondary side connects to the AGL fixture through the secondary connector and supplies the individual lighting load. There is no direct wire between the windings; energy crosses the core magnetically.
Q4Can an ordinary transformer replace an AGL isolating transformer?
No. An ordinary electrical transformer should not automatically be substituted. AGL transformers are selected for series-circuit operation, primary and secondary characteristics, power rating, insulation system, environmental exposure, mechanical construction, connector and fixture compatibility, and applicable standards and project requirements.
Q5What power ratings do AGL isolating transformers come in?
Ratings commonly encountered include 15 W, 25 W, 45 W, 65 W, 100 W, 150 W, 200 W, 300 W and 500 W. The required rating depends on the connected fixture or load and the applicable design requirements.
Q6How should an AGL isolating transformer be selected?
Selection should not be made from fixture wattage alone, or by choosing a higher rating for its own sake. The fixture load, required transformer rating and compatible series circuit must all line up, including secondary electrical requirements, primary series-circuit compatibility and CCR compatibility.
Q7Is 6.6 A the series-circuit current for every AGL system?
No. A nominal series-circuit current of 6.6 A is commonly encountered in many AGL applications, but the actual operating current depends on the specific system and design. Selection must be based on the applicable equipment specification and project design rather than one assumed universal current.
Q8Can a transformer's secondary power exceed its primary power?
No. For an ideal transformer primary power is approximately equal to secondary power, and in practice primary power is greater because of copper, core and dielectric losses. Real efficiency and losses must be taken from manufacturer data and verified by the applicable acceptance and test procedures.
Q9What is the main cause of AGL isolating transformer field problems?
Water ingress is one of the most important causes. Entry points include a damaged housing, the cable or lead interface, the connector interface, seal deterioration, mechanical damage and incorrect installation, leading to insulation degradation, corrosion, leakage current, earth fault and reduced life.
Q10What is inside an AGL isolating transformer?
An AGL isolating transformer generally contains a magnetic core, primary winding, secondary winding, insulation system, housing or enclosure, leads or connectors, a sealing system and identification markings. The exact construction varies by manufacturer and transformer design.
Q11How to test an AGL isolation transformer?
Isolate and secure the circuit under your site's permit-to-work, inspect the transformer, leads and connectors, then perform continuity and insulation resistance checks using the limits in the manufacturer's data and your project specification. Reconnect, energise under controlled conditions, confirm the fixture operates and record the results. Continuity alone does not prove a transformer is healthy.
Q12How to select an isolation transformer?
Start with the fixture and its load, then confirm the circuit current and CCR, the primary and secondary connector type, the installation location and the standard the unit must be approved to. Do not select on wattage alone. Check compatibility with the fixture and the CCR, and make sure the unit is approved to the specification your project follows.
Engineering & Expert Notes
A Transformer Failure Often Starts at the Lead or Connector
ConnectorsCheck the leads and moulded connectors first. Damage there is more common than a fault in the transformer itself.
Open Secondary Behaviour Depends on the Design
OperationDo not assume what happens when the secondary is open. Follow the manufacturer's guidance and the site's isolation procedure.
Match Wattage to the Actual Fixture Load
SelectionChoose the rating for the connected fixture with sensible margin, and check it again if the lamp or LED type changes.
Check Sealing and Water Entry in Wet Locations
WaterMoisture inside housings or connectors degrades insulation over time. Inspect seals and drainage during routine visits.
Test Insulation and Continuity Before Concluding It Has Failed
DiagnosisMeasured data separates a bad transformer from a bad cable or fixture and avoids replacing good parts.
Label and Record Replacements
RecordsIdentify transformer type and rating at each location in the register so the correct unit is fitted next time.
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Please read before relying on any content on this page or on any record downloaded from it.
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