SF/UTP (Screened Foiled Unshielded Twisted Pair)

What is SF/UTP?

SF/UTP (Screened Foiled Unshielded Twisted Pair) is a type of Ethernet cable that combines:

• An overall braided screen (S) surrounding all four pairs.
• An overall foil screen (F) beneath the braid.
• Unshielded twisted pairs (UTP) within the cable.

By combining both foil and braid shielding, SF/UTP provides excellent protection against electromagnetic interference (EMI) and radio frequency interference (RFI) whilst maintaining a simpler internal construction than S/FTP cable.

SF/UTP is commonly used in industrial environments, critical infrastructure, transportation systems, and high-interference installations where enhanced EMC performance is required.

SF/UTP Construction

Overall Braided Screen

• Tinned copper braid surrounding all four pairs.
• Provides excellent protection against lower-frequency electromagnetic fields.
• Improves mechanical durability.

Overall Foil Screen

• Aluminium/polyester foil located beneath the braid.
• Provides additional protection against high-frequency interference.
• Improves overall shielding effectiveness.

Unshielded Twisted Pairs

• Individual pairs are not separately screened.
• Signal integrity is maintained through pair twisting and the overall cable shielding.

Drain Wire

• Typically includes a drain wire beneath the foil screen.
• Assists with maintaining screen continuity.
• Simplifies termination and grounding.

Why Use SF/UTP?

Excellent EMI Protection

• The combined braid and foil screen offers significantly greater protection than F/UTP.
• Suitable for electrically noisy environments.

Improved EMC Performance

• The foil provides protection against high-frequency interference.
• The braid improves protection against lower-frequency interference.

Reduced Alien Crosstalk

• The dual-layer screen helps reduce interference between adjacent cables.
• Beneficial in high-density cable installations.

Simpler Than S/FTP

• Provides excellent EMC performance without individually screening each pair.
• Easier and faster to terminate than S/FTP.

SF/UTP vs Other Cable Types

Advantages of SF/UTP

Outstanding EMC Protection

• Provides excellent resistance to external interference sources.
• Well suited to industrial and critical infrastructure environments.

Improved Mechanical Strength

• Braided screens provide greater physical robustness than foil-only cables.

Reduced Installation Complexity

• Easier to terminate than individually screened pair cables.
• Fewer opportunities for termination errors compared to S/FTP.

Suitable for High-Speed Ethernet

• Commonly used for Cat6A and higher-performance installations.
• Supports 10 Gigabit Ethernet applications.

Limitations of SF/UTP

Larger Cable Diameter

• Typically larger and less flexible than F/UTP.
• May require larger containment systems.

Higher Cost

• More expensive than U/UTP and F/UTP designs.

Less Pair Isolation Than S/FTP

• Individual pairs remain unscreened.
• Does not provide the same pair-to-pair isolation as S/FTP.

Grounding Requirements

• Proper bonding and grounding remain essential for effective operation.

Screen Termination Requirements

Maintaining Screen Continuity

To achieve the intended EMC performance:

• Use screened patch panels.
• Use screened keystone modules.
• Use screened RJ45 connectors.
• Ensure foil and braid continuity throughout the channel.

A screened cable terminated with unscreened hardware may significantly reduce the effectiveness of the shielding system.

Functional Earthing

The screen assembly should be bonded to an appropriate Functional Earth (FE) through the structured cabling system.

This allows induced electrical noise to be diverted away from the data conductors and improves EMC performance.

Common Applications

Industrial Networks

• Manufacturing facilities
• Process control systems
• SCADA networks
• Utilities infrastructure

Critical Infrastructure

• Power distribution sites
• Water treatment facilities
• Gas transmission systems
• Rail infrastructure

Security Systems

• IP CCTV networks
• Perimeter security systems
• Access control infrastructure

Transport and Infrastructure

• Airports
• Ports
• Tunnels
• Roadside communications equipment

High-Density Cabling Installations

• Large communications rooms
• Equipment cabinets
• Data centre environments

Relevant Standards

ISO/IEC 11801

Defines SF/UTP cable construction and performance requirements.

BS EN 50173

European structured cabling standard.

BS EN 50310

Grounding and bonding requirements for ICT installations.

BS EN 50174

Installation practices for information technology cabling systems.

BS 6701:2016+A1:2017

Requirements for telecommunications cabling installations within buildings.

Installation Best Practices

1. Use Screened Components

• Match screened cable with screened connectors, patch panels, and outlets.

2. Maintain Shield Integrity

• Avoid damaging the foil or braid during termination.
• Follow manufacturer stripping instructions.

3. Observe Bend Radius Requirements

• Avoid crushing or excessively bending the cable.
• Follow manufacturer guidance.

4. Ensure Proper Bonding

• Bond cabinets, patch panels, and containment where required.
• Follow BS EN 50310 recommendations.

5. Test and Certify

• Verify:

  • Wire map
  • Length
  • NEXT
  • Return loss
  • Alien crosstalk
  • Shield continuity

SF/UTP vs S/FTP

SF/UTP is often selected when enhanced EMC protection is required but the additional complexity and cost of individually screened pairs is unnecessary.

When Should SF/UTP Be Used?

SF/UTP combines the benefits of both foil and braided shielding to provide excellent protection against electromagnetic interference whilst retaining a relatively simple cable structure. It is widely used in industrial, security, transport, and critical infrastructure applications where reliability and EMC performance are essential.