IN-BASE VS REMOTE
Two installation arrangements for the AGL isolation transformer — an in-base transformer is installed close to, or directly beneath, the associated fixture, while a remote transformer is installed at a separate location and connected to the fixture by a secondary cable. The choice mainly comes down to secondary-cable length, base space, and maintenance access.
At a Glance
| Feature | In-Base Transformer | Remote Transformer |
|---|---|---|
| Transformer location | In/near the light base | Separate remote location |
| Distance to fixture | Very short | Longer secondary cable |
| Secondary cable length | Short | Longer |
| Fixture-area excavation | Required | May be reduced at fixture location |
| Maintenance access | Requires access to base | May be easier at accessible remote location |
| Cable voltage-drop considerations | Lower due to short secondary run | More significant for longer secondary runs |
| Fault exposure | Located in pavement/ground environment | Can be in a more protected/accessible area |
| Installation arrangement | Compact, localized | Centralized or distributed remotely |
| Typical advantage | Minimal secondary cable length | Improved transformer accessibility |
Where the Transformer Sits
AGL FIXTURE
💡
──────────── PAVEMENT ────────────
│
[ LIGHT BASE ]
│
[ ISOLATION
TRANSFORMER ]
│
════════ PRIMARY CABLE ════════
AGL FIXTURE 💡
│
│ SECONDARY CABLE
│
▼
[ ISOLATION TRANSFORMER ]
│
════ PRIMARY SERIES CABLE ════
Easy memory: in-base = transformer under the light. Remote = transformer away from the light.
Typical AGL Circuit Arrangement
In-Base Arrangement
CCR │ ▼ PRIMARY SERIES CABLE │ ▼ [ ISOLATION TRANSFORMER ] │ ▼ SHORT SECONDARY │ ▼ AGL LIGHT 💡
The secondary connection between the transformer and fixture is short.
Remote Arrangement
CCR │ ▼ PRIMARY SERIES CABLE │ ▼ [ ISOLATION TRANSFORMER ] │ ▼ LONGER SECONDARY CABLE │ ▼ AGL LIGHT 💡
The secondary circuit extends from the remote transformer to the fixture.
The Most Obvious Electrical Difference
In-Base Transformer
TRANSFORMER
│
▼
SHORT
SECONDARY
│
▼
FIXTURE 💡
Advantages can include:
- Reduced secondary cable length
- Fewer secondary-cable routing requirements
- Reduced cable exposure
Remote Transformer
TRANSFORMER
│
▼
════════════════════
SECONDARY CABLE
════════════════════
│
▼
FIXTURE 💡
The longer secondary connection must be properly considered for:
- Electrical losses
- Cable condition
- Mechanical protection
- Fault location
- Installation environment
Reaching the Transformer
Transformer in Base
PAVEMENT
────────────
FIXTURE
│
REMOVE LIGHT
│
ACCESS BASE
│
TRANSFORMER
Maintenance may require opening or accessing the light-base area.
Remote Transformer
REMOTE ACCESS AREA
│
▼
TRANSFORMER
│
▼
INSPECT / REPLACE
If located in an accessible handhole, pit, or equipment area, maintenance can be easier.
Main advantage: remote installation can improve physical access to the isolation transformer.
What the Transformer Must Withstand
In-Base
PAVEMENT
────────────
│
[ TRANSFORMER ]
│
GROUND / BASE
The installation must withstand conditions associated with underground or pavement-base environments:
- Water
- Moisture
- Cable connections
- Drainage
- Contamination
Remote
PROTECTED /
ACCESSIBLE AREA
│
[ TRANSFORMER ]
A remote transformer can potentially be installed in an environment selected for:
- Better accessibility
- Improved drainage
- Easier inspection
However, remote installation still requires suitable environmental protection.
Tracing a Light Failure
In-Base
LIGHT FAILURE
│
▼
OPEN LIGHT BASE
│
▼
CHECK TRANSFORMER
The transformer is physically close to the fixture, simplifying identification of the associated equipment.
Remote
LIGHT FAILURE
│
▼
CHECK SECONDARY CABLE
│
▼
CHECK REMOTE
TRANSFORMER
A longer secondary cable introduces another section that may need to be checked.
Building the Circuit
In-Base Transformer
INSTALL BASE
│
▼
INSTALL TRANSFORMER
│
▼
CONNECT FIXTURE
The installation is concentrated at the fixture location.
Remote Transformer
INSTALL TRANSFORMER
AT REMOTE POINT
│
▼
ROUTE SECONDARY
CABLE
│
▼
CONNECT FIXTURE
The installation requires additional secondary cable routing.
What the Base Must Hold
LIGHT BASE ┌─────────────┐ │ FIXTURE │ ├─────────────┤ │ TRANSFORMER │ └─────────────┘
LIGHT BASE ┌─────────────┐ │ FIXTURE │ └─────────────┘ REMOTE LOCATION ┌─────────────┐ │ TRANSFORMER │ └─────────────┘
The in-base arrangement requires the base to have sufficient internal space for the transformer, connectors, and secondary wiring. In the remote arrangement, the fixture base may require less internal equipment space.
Same Principle, Different Location
CCR │ ▼ PRIMARY SERIES CIRCUIT │ ▼ ISOLATION TRANSFORMER │ ▼ SECONDARY CIRCUIT │ ▼ AGL FIXTURE
The transformer location does not change the fundamental purpose of the isolation transformer. In both cases it couples the primary series circuit to the fixture circuit, provides electrical isolation, and supplies the fixture at the required secondary current characteristics. The major difference is physical location and secondary-cable arrangement.
Full Engineering Parameters
| Parameter | Transformer in Base | Remote Transformer |
|---|---|---|
| Distance from fixture | Very short | Longer |
| Secondary cable | Short | Longer |
| Transformer accessibility | More limited | Potentially better |
| Secondary-cable exposure | Lower | Higher |
| Base space requirement | Higher | Lower |
| Installation concentration | At fixture | Distributed |
| Fault investigation | Localized | May include cable route |
| Transformer replacement | Requires base access | May be easier remotely |
| Pavement-area equipment | More | Less |
Choosing the Right Arrangement
IS MINIMUM SECONDARY
CABLE LENGTH IMPORTANT?
│
┌────┴────┐
│ │
YES NO
│ │
▼ ▼
IN-BASE IS EASY TRANSFORMER
MAY BE ACCESS IMPORTANT?
PREFERRED │
▼
REMOTE MAY
BE PREFERRED
Other factors include:
- Light-base dimensions
- Pavement construction
- Maintenance philosophy
- Drainage
- Secondary cable routing
- Accessibility
- Applicable AGL standards
- Manufacturer-approved installation arrangements
Myths vs Facts
Not necessarily. The transformer can have the same electrical rating and isolation function. The difference is primarily location: in-base is close to the light, remote is away from the light.
Not always. The transformer is close to the fixture, but accessing it may require opening the light base.
Not necessarily. The effect depends on secondary cable length, cable size, current, transformer rating, and fixture load. The secondary circuit must simply be designed within the applicable electrical limits.
In-Base vs Remote Transformer
Isolation transformer in base = transformer installed at or immediately adjacent to the AGL fixture, providing a short secondary connection.
Remote transformer = transformer installed at a separate location, requiring a longer secondary cable but potentially providing better access for maintenance. For AGL installations, the best arrangement depends mainly on secondary-cable length, base space, pavement constraints, drainage, transformer accessibility, and maintenance strategy.
Both arrangements use the same basic AGL principle — the transformer location does not change its fundamental purpose. The final choice must always follow the governing standard and approved installation design, not a general rule of thumb.
Engineering & Expert Notes
Check Secondary Cable Length Against the Design
DesignLonger secondaries add voltage drop and exposure. Verify against the transformer and fixture requirements.
Plan Access for Replacement
MaintenanceThink about how a unit will be reached and changed in service.
Look at Moisture Exposure for Each Location
EnvironmentChoose arrangements that keep connectors and units out of standing water.
Label the Arrangement on Drawings
RecordsShow where each transformer sits so fault finding starts from correct information.
Frequently Asked Questions
An in-base transformer is installed close to, or directly beneath, the associated AGL fixture, while a remote transformer is installed at a separate location and connected to the fixture by a longer secondary cable.
Not necessarily. The transformer can have the same electrical rating and isolation function in both arrangements — the difference is primarily location and secondary-cable length.
It depends. A remote transformer located in an accessible handhole, pit, or equipment area can be easier to service, while an in-base transformer requires opening or accessing the light base.
Not necessarily. The effect depends on secondary cable length, cable size, current, transformer rating, and fixture load — the secondary circuit simply needs to be designed within the applicable electrical limits.
The base must accommodate the transformer, connectors, and secondary wiring alongside the fixture itself, whereas a remote arrangement keeps that equipment at a separate location.
For an in-base transformer, a light failure typically means opening the light base to check the transformer directly. For a remote transformer, the secondary cable route must also be checked in addition to the transformer itself.
Governing Documents
For an actual project design, always verify the current edition of the applicable documents.
FAA AC 150/5345-42
Specification for Airport Light Bases, Transformer Housings, Junction Boxes, and Accessories — including isolation transformer installation arrangements.
ICAO Annex 14, Volume I
Aerodrome Design and Operations — general requirements for series-circuit AGL systems and isolation transformer arrangements.
DGCA / AAI Requirements
For Indian airport projects, also verify applicable DGCA requirements, AAI requirements, airport-specific technical specifications, project drawings and contract specifications.
Final Engineering Note
Do not select a transformer arrangement from a generic web diagram. The final installation drawing should always be developed from the current governing standard, approved airport design, and manufacturer-approved arrangement.
In-base placement is not the only correct approach, and remote placement is not automatically superior — each is selected to balance secondary-cable length, base space, drainage, and maintenance access for the specific installation.
Compare the Systems. Then Learn How to Engineer Them.
Understanding the difference between AGL systems is the first step. The next step is knowing how to design, install, test, commission and maintain them correctly.
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