Cat6a S/FTP: Double Screening
Quick answer / TL;DR: Short answer: S/FTP screens each pair with foil and the bundle with braid, giving the best immunity of the twisted-pair family. Specify it for high-interference environments such as drive cabinets and broadcast areas; elsewhere F/UTP is usually enough. Both need the shield bonded at the panel, and S/FTP's diameter and stiffness must be planned for.
Cat6a S/FTP has two levels of screening: a foil around each pair and a braid around all four. The stack is built for environments where one screen is not enough – drive cabinets, radio equipment, plant rooms – and it costs diameter, stiffness and a grounding obligation.
This is the S/FTP guide: what the second screen actually stops, when the extra cost is justified, and the bonding that completes the system.
The Shield Stack
| The layer | The material | The function |
|---|---|---|
| Pair screen | Foil per pair | Stops coupling between pairs |
| Overall screen | Braid | Stops external interference |
| Drain | Wire in contact with foil | Carries the screen to ground |
| Jacket | Outer compound | Mechanical protection |
The two screens address different problems: pair-to-pair coupling inside the cable, and external fields outside it.
When the Second Screen Is Justified
- Drive cabinets and motor control centres
- Broadcast and RF environments
- Routes alongside welding or induction equipment
- Plant rooms with variable-frequency drives
- Not for ordinary office routes – F/UTP suffices
The justification is measured interference, not a preference for the best specification on the datasheet.
The Costs
| The cost | The effect |
|---|---|
| Diameter | Fewer cables per tray |
| Stiffness | Tighter bend radius, slower pulls |
| Termination | Shielded jacks and careful bonding |
| Price | Higher per metre than F/UTP |
Standards and Verification
| The reference | The relevance |
|---|---|
| ISO/IEC 11801-1 | Screening classes and S/FTP definition |
| TIA-568.2-D | Bonding practice |
| IEC 61156 | Cable construction |
| Field test | Channel test plus bond continuity |
Per-SKU screen coverage is not provided in the knowledge base. The construction definition is standard; verify the datasheet and test the bond.
Real-World Applications
The motor control room
A motor control room wired in S/FTP: pair foils plus braid, bonded shells, every link tested – the communication faults that had plagued the line stopped appearing.
Related reading: The Cat6a shielding choice — blogs/news/cat6a-shielded-cable
Related reading: Identifying a shielded cable in the field — blogs/news/shielded-cable-identification
Frequently Asked Questions
What does S/FTP mean?
Screened foiled twisted pair: foil around each pair plus an overall braid.
Is S/FTP better than F/UTP?
For immunity in high-interference areas, yes; for ordinary offices the difference is not measurable.
Does S/FTP need grounding?
Yes – both screens must reach ground through the jack, panel and rack.
Is S/FTP harder to install?
Yes: larger diameter, stiffer, and slower shielded terminations.
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