What are twisted pair cables? Comparing UTP and STP cables

A twisted pair cable is a type of cable commonly used in telephone systems and most modern Ethernet networks. It consists of two insulated copper wires twisted together to form a circuit that transmits signals. The twisting reduces crosstalk - interference caused by adjacent wire pairs.

When current flows through a wire, it creates a small circular magnetic field around it. By placing two wires close together and twisting them, their magnetic fields cancel each other out, minimizing external interference. This design technique enhances the cable’s ability to resist EMI. The result is a “self-shielding” effect, achieved by combining wire twisting and signal cancellation, which protects each pair from noise.

Twisted pair cables are the most cost-effective cabling option used in local area networks (LANs). They are widely employed in data transmission and applications where signal noise immunity is required.

There are two basic types of twisted pair cables:

• UTP (Unshielded Twisted Pair)
• STP (Shielded Twisted Pair)

>>See more: Overview of LAN and type of LAN cables

2.1 What are UTP cables?

UTP cable is a type of network cable consisting of twisted copper wire pairs enclosed in an outer protective sheath. Its defining feature is the twisting of wire pairs, which helps reduce interference from external sources. Thanks to this design, UTP cables can transmit data reliably and are widely used across various networking applications.

UTP relies solely on the cancellation effect between twisted pairs to minimize signal degradation from EMI and radio frequency interference (RFI). Each twisted pair in a UTP cable typically has a different twist rate to reduce crosstalk.

In network installations, UTP cables are commonly terminated with RJ45 connectors - 8-pin connectors used extensively for Ethernet LAN connections.

Computer network UTP cables typically contain four twisted pairs of copper wires, with conductor sizes of 22 or 24 AWG. These cables have a characteristic impedance of 100 ohms, which distinguishes them from telephone twisted pair cables with about 600 ohms impedance.

2.2 Advantages and disadvantages of UTP cables

Advantages:

• Compact size, with an outer diameter of around 0.43 cm (0.17 inches), making installation easier - especially in space-constrained environments.
• Easy to install and bend, with lower costs compared to other network cables.
• Widely compatible with common networking standards, making UTP the most prevalent choice.

Disadvantages:

• More susceptible to electromagnetic and radio frequency interference than coaxial or fibre optic cables.
• Shorter signal transmission distances due to higher attenuation compared to coaxial or fibre optic cables.

3.1 What are STP cables?

STP (Shielded Twisted Pair) cable is also a type of twisted pair cable, but with an added shielding layer around each wire pair. This shielding reduces EMI, crosstalk, and signal leakage - making it ideal for protecting networks from external noise.

In Ethernet networks, STP helps mitigate both internal crosstalk and external noise such as EMI and RFI. While STP cables often require specialized connectors, they can sometimes be used with standard RJ45 connectors under certain conditions.

Despite their superior noise protection, STP cables are more expensive and complex to install. The shielding must be grounded properly at both ends; otherwise, it may act like an antenna and attract interference instead. Due to the higher cost and complex grounding requirements, STP is rarely used in typical Ethernet deployments today.

>>See more: What is crosstalk? How to prevent crosstalk?

3.2 Advantages and disadvantages of STP cables

Advantages:

• Superior interference protection: The shielding significantly reduces external EMI and RFI, making STP ideal for industrial environments.
• Signal integrity: Reduced crosstalk and attenuation help maintain high-speed, stable data transmission.
• Longer transmission distances: STP can transmit data over greater distances without signal degradation, suitable for large-scale networks.

Disadvantages:

• Higher cost: Due to its more complex structure and shielding, STP is more expensive than UTP.
• Lower flexibility: The metallic shielding reduces flexibility, making STP harder to bend and install in tight spaces.

4.1 Similarities

Both UTP and STP cables share these common traits:

• Twisted pair structure: Designed to reduce interference and crosstalk.
• Used in Ethernet networks: Common in LANs including Fast Ethernet and Gigabit Ethernet.
• RJ45 connector compatibility: Both can be terminated with RJ45 connectors.
• Support for multiple standards: Compatible with various networking standards and speeds.
• Distance limitations: UTP typically supports up to 100 meters; STP can reach up to 1000 meters under optimal conditions.