Introduction

When planning a KNX-based smart home or building automation system, one of the most important decisions you will face is how your KNX devices will communicate with each other. KNX offers multiple communication media, but the two most commonly used are:

• KNX TP (Twisted Pair)
• KNX IP (Internet Protocol over Ethernet)

Both options follow the KNX standard and ensure interoperability, but each has unique characteristics that make it suitable for specific types of installations.

Whether you’re an engineer designing a large building automation system or a homeowner considering smart lighting and HVAC control, understanding the differences between KNX TP and KNX IP will help you make the right choice.

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What is KNX TP (Twisted Pair)?

KNX TP stands for KNX over Twisted Pair cable, and it is the most traditional and widely used form of communication in KNX installations. The communication takes place over a dedicated 2-wire cable that follows a standard format, often referred to as the KNX bus cable.

Key Characteristics:

• Two wires carry both data and power, typically 30V DC.
• It supports a decentralized topology, meaning any device (sensor, switch, actuator) can send or receive messages.
• Supports 64 devices per line, but the number can be increased by adding line repeaters or line couplers.
• Topology must follow line or tree structure. Star or ring topologies are not supported.

Advantages:

• No need for additional power cables for low-energy devices (switches, sensors).
• Proven stability and reliability, even in harsh electrical environments.
• Simple installation, especially in residential projects.

Limitations:

• Communication speed is slow (9600 bps), but sufficient for control tasks.
• Limited scalability without additional infrastructure.
• Not suitable for direct integration with IT systems or remote monitoring over internet.

KNX TP is ideal for standalone residential or small commercial projects where performance and simplicity are the priorities.

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What is KNX IP (Internet Protocol)?

KNX IP enables KNX communication over standard Ethernet or IP-based networks. Instead of using a special twisted-pair cable, devices communicate through your existing LAN infrastructure using routers, switches, and standard CAT cables.

KNX IP is not meant to replace TP but to enhance connectivity, speed, and integration with IT systems. It is especially useful in large installations where multiple KNX lines must be connected or when remote access is needed.

Key Characteristics:

• Devices communicate over standard Ethernet or Wi-Fi networks.
• Requires KNX IP routers or interfaces to connect IP and TP systems.
• Suitable for remote programming, diagnostics, and visualization.
• Communication speed is significantly faster than TP.

Advantages:

• Fast data transmission and low latency.
• Seamless integration with IT and BMS systems (e.g., via BACnet or Modbus).
• Ideal for connecting multiple KNX lines in large buildings.
• Enables remote access via internet or VPN for diagnostics and updates.

Limitations:

• Requires separate power supply or Power over Ethernet (PoE) infrastructure.
• More expensive cabling and networking devices (Ethernet switches, routers).
• Slightly more complex to set up compared to TP.

KNX IP is the preferred solution for large-scale or IP-integrated smart buildings that demand speed, scalability, and remote management.

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Side-by-Side Comparison: KNX TP vs KNX IP

Feature	KNX TP (Twisted Pair)	KNX IP (Ethernet/IP)
Physical Medium	2-wire KNX bus cable	Ethernet (CAT5/6) or Wi-Fi
Power Over Bus	Yes – powers sensors, switches, etc.	No – needs PoE or separate power
Communication Speed	~9600 baud	10/100 Mbps or more
Topology	Line or tree	Star or full IP network
Max Devices Per Line	64 (expandable with repeaters)	Unlimited (network dependent)
Configuration Tool	ETS software (via USB or serial)	ETS software (via KNX IP interface)
Best Use Case	Homes, small buildings	Large buildings, campuses, remote programming
Interference Resistance	High (suitable for electrical rooms)	Moderate (shielded cables recommended)
Integration with BMS	Requires gateways	Direct integration via IP
Remote Access	Not built-in	Yes – with KNX IP Interface or secure router

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When Should You Choose KNX TP?

KNX TP is best for situations where:

• You are installing a medium to small-sized system, like a home, apartment, or small office.
• Devices are physically close, and long cable runs are not required.
• Power over bus is needed to reduce wiring complexity (e.g., for wall switches).
• The system does not need internet access or IP integration.

Example Projects:

• A luxury villa with automated lighting, climate, and shutters.
• A small retail store with KNX sensors and dimmable lighting.
• Retrofits where twisted-pair wiring is easier to install than Ethernet.

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When Should You Choose KNX IP?

KNX IP is ideal in environments where:

• You are working on a large or multi-building project (campus, hotel, airport).
• Integration with IT systems or building management platforms is required.
• You need to remotely access or program the KNX system via the internet.
• Fast and large data exchanges are part of the system (e.g., visualization servers).

Example Projects:

• A hotel using KNX IP to control lighting and climate in every room, connected via a central server.
• A commercial office building with multiple TP lines connected via IP routers.
• A smart school using a combination of KNX IP and visualization tools for energy monitoring.

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Can KNX TP and KNX IP Work Together?

Yes. In fact, most professional KNX installations use both.

A typical setup looks like this:

• Field devices (like sensors, actuators, and switches) are connected using TP.
• KNX IP Routers are used to link multiple TP lines and provide access to the KNX backbone over IP.
• KNX IP Interfaces are used to program and monitor the system from a computer on the local network.

This hybrid approach gives you the cost savings and reliability of TP in the field, combined with the scalability, speed, and remote access of IP.

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Top KNX Brands Offering TP and IP Devices

Brand	KNX TP Devices	KNX IP Devices
Gira	Switches, motion sensors, actuators	IP Routers, IP Interfaces
MDT	Actuators, push-buttons	Secure IP Interface, IP Router
ABB	Dimming modules, fan coil controllers	IP Router, KNXnet/IP server
Jung	Room controllers, thermostats	IP Interface
Theben	Presence detectors, timers	IP Interfaces, secure gateways
Siemens	HVAC and lighting modules	IP Backbone couplers

These brands offer ETS-compatible devices for both TP and IP, making it easy to design hybrid systems.

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Conclusion:

Choosing between KNX TP and KNX IP both depends entirely on the size of your project, technical requirements, and desired functionality.

Choose KNX TP if:

• You want a simple, robust solution for homes or smaller installations.
• You need power and communication on the same cable.
• Budget and ease of wiring are top priorities.

Choose KNX IP if:

• You need to connect multiple buildings or floors.
• Remote diagnostics or programming are important.
• You want fast communication and integration with modern IT systems.

Use both in combination if:

• You want to build a future-proof KNX system that can scale easily.
• Your system will grow over time and may need remote management or centralized control.

In smart building design, the ideal solution is usually a hybrid system that uses KNX TP in the field and KNX IP at the backbone level.