Screened Cable VS Unscreened Cable
Screened cable is cable built with a conductive screen/shield around the conductor, aimed at electric-field control, EMI management and cable/system protection. Unscreened cable has no conductive screen and relies on its insulation and outer construction alone. Whether an AGL series cable should be screened or unscreened is not a fixed rule — it depends on the circuit design, voltage rating, EMC requirements and the applicable project specification.
At a Glance
| Feature | Screened Cable | Unscreened Cable |
|---|---|---|
| Conductive screen | Yes | No |
| Main purpose | Shielding / field control | Basic insulation and protection |
| EMI control | Better | Lower |
| Electric-field containment | Better | Limited |
| Construction | More complex | Simpler |
| Diameter | Generally larger | Generally smaller |
| Weight | Generally higher | Generally lower |
| Cost | Generally higher | Generally lower |
| Termination | More involved | Simpler |
| AGL suitability | Application/specification dependent | Application/specification dependent |
What Is Screened & Unscreened Cable?
Screened Cable
Cable built with a conductive layer around the insulated conductor, typically copper tape, copper wire, aluminium or another conductive construction, depending on the cable design.
Main characteristics
- Conductive screen surrounds the insulation
- Aimed at electric-field control and EMI reduction
- Screen effectiveness depends on construction, continuity and earthing
- Requires correct screen termination and bonding
Unscreened Cable
Cable with no conductive screen around the insulated conductor, relying on its insulation and outer protective construction alone.
Main characteristics
- No conductive shield layer
- Simpler, lighter construction in most designs
- No screen-termination or bonding requirement
- Relies on insulation and sheath for basic protection
The Biggest Difference
The easiest way to remember the difference between screened and unscreened cable:
Screened Cable
Conductor → insulation → conductive screen → outer sheath
Unscreened Cable
Conductor → insulation → outer sheath
Easy memory: Screened → conductor + insulation + shield. Unscreened → conductor + insulation.
Construction Compared
Screened Cable
The screen sits between the insulation and the outer sheath, wrapping the insulated conductor in a conductive layer.
Unscreened Cable
No conductive layer is present — the insulation sits directly beneath the outer sheath.
Field Control & Earthing Function
The screen can help control the electric field surrounding the cable and can provide a controlled path for certain unwanted electrical currents when correctly bonded and grounded. For shield effectiveness, the screen's construction, continuity and termination/earthing arrangement are all important — a screen that is present but poorly terminated does not deliver the intended benefit.
Simply having a screen does not guarantee effective shielding. An incorrectly terminated or poorly bonded screen can reduce the intended effectiveness of the construction.
How Screening Affects Electromagnetic Coupling
| Condition | Screened Cable | Unscreened Cable |
|---|---|---|
| Coupling with surrounding equipment | Reduced by the conductive screen | No conductive barrier present |
| Path for unwanted currents | Controlled, when correctly bonded/earthed | Not provided |
| Dependence on termination | Effectiveness depends on correct bonding | Not applicable |
| Typical use case | Electrically demanding or EMC-sensitive environments | Simpler installations without a specified EMC need |
Where This Sits in an AGL Circuit
Simplified AGL Circuit
Whether the AGL series cable in this circuit should be screened or unscreened depends on the specific AGL circuit design, cable voltage rating, airport/project specification, applicable standard, EMC requirements, installation arrangement and the manufacturer's cable specification.
Do not assume that every AGL series cable must be screened. The requirement comes from the applicable design and specification, not from a general assumption.
Electrical Isolation vs Screening
These are completely different concepts, even though both appear in the same AGL circuit context.
Isolation
Provided by an isolation transformer through magnetic coupling between primary and secondary windings — it separates circuits electrically.
Screening
Provided by a conductive layer around the cable — it addresses electric-field control and EMI, not electrical separation.
Screening does not mean electrical isolation, and an isolation transformer does not automatically mean the cable is screened. The two functions are independent of each other.
The Extra Step Screened Cable Requires
A screened cable carries an additional installation requirement beyond that of an unscreened cable: the screen itself must be correctly terminated and bonded or earthed according to the cable and system design. An incorrectly terminated screen can reduce its intended effectiveness, so this step is not optional where a screen is present.
Screened Cable
- Screen must be correctly terminated
- Requires bonding/earthing per the system design
- Poor termination reduces effectiveness
Unscreened Cable
- No screen-termination step required
- Simpler termination overall
- Relies on standard insulation/sheath termination practice
What Each Construction Offers
Screened Cable
Potential advantages
- Better control of electric fields
- Improved EMC performance
- Reduced electromagnetic coupling
- Controlled screen/earth connection where required
- Useful in electrically demanding environments
Trade-offs
- Higher cost
- More complex termination
- Greater diameter/weight in many designs
- Requires correct screen bonding
Unscreened Cable
Potential advantages
- Simpler construction
- Easier termination
- Lower cost
- Smaller/lighter construction in many cases
- No screen termination required
Trade-off
- Does not provide the additional shielding/field-control function of a screened construction
Full Comparison Table
| Parameter | Screened Cable | Unscreened Cable |
|---|---|---|
| Conductive shield | Yes | No |
| Electric-field control | Better | Basic |
| EMI protection | Better | Lower |
| Cable construction | More complex | Simpler |
| Termination | More demanding | Easier |
| Cost | Generally higher | Generally lower |
| Diameter/weight | Generally greater | Generally lower |
| AGL use | Only where specified/required | Where specified/appropriate |
Choosing the Right Construction
For an AGL installation, the choice between screened and unscreened cable should follow this sequence, not a general preference for one construction over the other:
- AGL circuit design
- Operating voltage
- Current
- Installation environment
- EMC / screening requirement
- Cable construction
- Project specification
The choice should come from the specified cable type, rather than assuming screened is always better.
Myths vs Facts
Whether an AGL cable should be screened depends on the specific circuit design, voltage rating, project specification and EMC requirements — it isn't a fixed rule.
Screening addresses electric-field control and EMI; electrical isolation is a separate function provided by an isolation transformer through magnetic coupling.
Shield effectiveness depends on the screen's construction, continuity and correct termination/bonding — an incorrectly terminated screen can reduce its intended effectiveness.
Screened cable carries higher cost, more complex termination and generally greater diameter/weight — the correct choice is whatever the AGL circuit design and project specification call for.
Which Construction Applies Where?
Screened cable adds a conductive layer around the insulated conductor for electric-field control and EMI management, at the cost of a more complex, heavier and more expensive construction that also requires correct screen termination and bonding. Unscreened cable is a simpler, lighter and lower-cost construction that relies on its insulation and outer sheath alone, without the additional shielding function.
For AGL, don't select screened cable merely because it offers more protection. Use the cable construction specified for the particular AGL circuit, voltage, installation and applicable project/airport requirements.
Engineering & Expert Notes
Follow the Termination Method for the Screen
TerminationPoor screen termination defeats the purpose and can create hazards.
Check Earthing of the Screen
EarthingVerify how and where the screen is earthed, as designed.
State the Cable Type in the Specification
SpecificationDo not leave it implied.
Test Screens as Well as Conductors
TestingInclude screen continuity checks where applicable.
Frequently Asked Questions
Screened cable has a conductive layer around the insulated conductor for field control and EMI reduction; unscreened cable has no such layer and relies on its insulation and outer sheath alone.
No. Whether AGL series cable should be screened depends on the specific circuit design, cable voltage rating, project/airport specification, applicable standard, EMC requirements and installation arrangement.
No. Screening and isolation are different concepts — isolation is provided by an isolation transformer through magnetic coupling, while screening is a conductive layer addressing field control and EMI.
Not automatically. Shield effectiveness depends on the screen's construction, continuity and correct termination/bonding arrangement — a poorly terminated screen reduces its intended effectiveness.
The screen must be correctly terminated and bonded/earthed according to the cable and system design — a requirement that unscreened cable does not have.
Generally, yes — screened cable typically has a greater diameter/weight and higher cost due to the additional conductive layer and more involved termination, though the exact difference is design-dependent.
By following the AGL circuit design, operating voltage, current, installation environment, EMC/screening requirement and project specification — not by assuming screened cable is always the better option.
Governing Documents
For an actual airport project, verify the current applicable editions of the relevant standards and the specific cable manufacturer's datasheets before using this comparison for project design.
ICAO Annex 14, Volume I
Aerodrome Design and Operations — general electrical requirements relevant to AGL series circuits and cable construction.
ICAO Aerodrome Design Manual
Applicable material covering series-circuit design, cable insulation and EMC/screening considerations for AGL infrastructure.
National CAA / 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
Whether a given AGL cable should be screened or unscreened, and the exact screen construction/earthing arrangement, can vary with the governing standard, equipment manufacturer and approved airport design. For final design, use the current applicable standard and manufacturer datasheets rather than a generic comparison page.
Screened cable adds a conductive shield for field/EMC control at the cost of complexity and price; unscreened cable is simpler and cheaper but has no shielding function — the correct choice for AGL comes from the circuit design and project specification, not a default assumption.
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