The KNX cable plays a critical role in the bus system, which is widely used in building automation for controlling lighting, heating, ventilation, security, and other smart functions. As the foundation for communication between devices in a installation, understanding the types of KNX cables, their characteristics, and proper installation techniques is essential for ensuring optimal performance, reliability, and longevity of your KNX system. In this guide, we will explore everything you need to know about KNX cables, including types, specifications, installation tips, and best practices.
What is KNX Cable?
KNX cable refers to the twisted pair cable used to connect devices within the KNX bus system. It facilitates the transmission of data and power across the network, ensuring that devices like sensors, actuators, controllers, and interfaces can communicate with each other seamlessly. The cable is specially designed for the needs of the KNX protocol, offering features that support the reliability and efficiency required in building automation systems.
While KNX TP (Twisted Pair) is the most common type of cable used in KNX systems, other transmission media such as Powerline (PL), RF (radio frequency), and IP can also be used, but these require different configurations and hardware.
Generic KNX Cable Specification
- Standard Compliance:
- EN 50090, IEC 60332, IEC 60754, CPR, RoHS
- Certified for use in KNX bus installations
- Conductor:
- Solid bare copper
- Typical size: 2 × 2 × 0.8 mm (twisted pairs)
- DC resistance ≤ 75 Ω/km (per conductor)
- Insulation:
- Polyethylene (PE) or Foam-Skin PE
- Colour-coded cores (commonly Red, Black, White, Yellow or Green)
- Shielding:
- Aluminium/PET foil screen with ≥100% coverage
- Tinned copper drain wire for grounding
- Sheath:
- Inner: Halogen-Free Flame Retardant (HFFR/LSZH)
- Outer: PVC or LSZH, UV and moisture resistant
- Typical colour: Green (RAL 6018, KNX standard)
- Electrical Characteristics:
- Operating voltage: 300/500 V or 450/750 V (depending on type)
- Test voltage: ≥2 kV / 5 min
- Insulation resistance: ≥200 MΩ·km
- Capacitance: ≤100 nF/km
- Mechanical Properties:
- Operating temperature: -20°C to +70°C
- Minimum bend radius: ≥8 × cable diameter
- Typical overall diameter: 6–8 mm (standard), 12–13 mm (armoured cable)
- Installation:
- Suitable for fixed indoor installations in walls, ducts, and ceilings
- Can be laid alongside power cables with adequate separation
- Available in standard lengths: 100 m, 200 m, 500 m
Types of KNX Cable
The two most commonly used types of KNX cables are TP and Powerline (PL), though other media like RF and IP are sometimes used depending on the installation requirements.
1. KNX TP (Twisted Pair) Cable
- Most Common Type: TP cable is the primary cable used in wired installations. It is a two-wire twisted pair cable that transmits both power and data.
- Construction: Typically, a shielded twisted pair (STP) or unshielded twisted pair (UTP) design is used, with shielding offering better protection against electromagnetic interference (EMI), ensuring more stable communication, especially in areas with high electrical noise.
- Specifications: The standard for TP cables is defined by the Association. It usually have a nominal impedance of 120 ohms, suitable for long-distance communication with minimal signal loss.
- Use Case: This cable is widely used for most commercial, residential, and industrial KNX installations.
2. KNX Powerline (PL) Cable
- Powerline Communication: KNX Powerline is used in installations where it is difficult or impractical to lay new twisted pair cables. Instead, Powerline uses existing AC power cables to transmit data over the electrical wiring of the building.
- Signal Transmission: The PL system enables devices to communicate via the existing power grid, allowing data to pass through circuits without needing a dedicated cable.
- Specifications: Powerline communication uses the standard HomePlug or PLC protocols for data transmission over the power grid.
- Use Case: Ideal for retrofitting projects or installations where traditional cabling is not feasible.
Key Specifications of KNX Cable
KNX cables must meet specific electrical and mechanical standards to ensure reliable communication and performance. Some of the important specifications to consider when selecting and installing cables include:
1. Impedance
- TP cables typically have an impedance of 120 ohms, which is crucial for ensuring that the electrical signals are transmitted with minimal signal reflection or loss.
2. Shielding
- Shielded twisted pair (STP) cables are preferred for KNX installations, especially in environments with high electrical interference (e.g., near large machinery, industrial environments, or in buildings with many electrical devices). The shielding helps protect the signal from external noise and ensures stable communication.
- Unshielded twisted pair (UTP) cables may be used in low-interference environments, but they provide less protection against EMI.
3. Cable Length
- The maximum distance for KNX cables depends on the type of cable and the number of devices connected to the bus. Typically, TP cables can run up to 1000 meters with a maximum of 64 devices on a single bus line, though additional repeaters or couplers may be used to extend the range.
4. Voltage
- KNX cables operate at a low voltage of 24V DC, and the power supply typically provides the necessary current to ensure stable operation across the network.
5. Temperature Range
- KNX cables are designed to withstand a range of environmental conditions. Typical temperature ranges are from -5°C to +60°C, but cables should be chosen based on the installation environment (e.g., outdoor, underground, industrial settings).
Installation Best Practices
Proper installation of KNX cables is crucial to ensure the system works optimally and remains reliable over time. Here are some best practices to consider during installation:
1. Cable Routing
- Always route cables away from sources of interference such as high-voltage cables, electrical panels, and large motors. This helps to maintain signal integrity and reduces the risk of communication errors.
- Use cable trays, conduits, or ducts to keep cables organized, especially in larger installations, and ensure that cables are adequately protected from mechanical damage.
2. Minimum Bend Radius
- Avoid sharp bends or tight loops in the cables, as this can cause signal degradation or damage the internal wires. Always follow the minimum bend radius specified by the cable manufacturer.
3. Separation from High Voltage Cables
- Keep KNX cables at least 10-20 cm away from high-voltage cables (e.g., 230V AC circuits). This prevents electromagnetic interference (EMI) and ensures stable data transmission.
4. Grounding and Shielding
- Proper grounding and shielding are essential in installations with high electromagnetic interference (EMI). Make sure to use shielded cables (STP) in environments with significant electrical noise to maintain the integrity of the communication signals.
5. Cable Length and Device Count
- When planning the layout of the system, ensure that the cable length does not exceed the maximum recommended distance . Maximum cable length (typically 1000 meters for TP). Use repeaters or couplers if longer distances or more devices are required.
Applications
1. Residential Automation
- In homes, KNX cables are used to connect devices like lighting, heating, cooling, shading systems, and security sensors, providing seamless control through centralized or distributed automation.
2. Commercial Buildings
- In office buildings, shopping malls, or hotels, KNX cables help integrate lighting systems, HVAC, and energy management systems, providing centralized control and optimizing energy efficiency.
3. Industrial Automation
- For industrial applications, this cables are used to automate and control systems like lighting, access control, and energy monitoring in factories, warehouses, and plants.
4. Smart Buildings
- Cables are integral to the automation of modern smart buildings. Help integration with third-party systems, such as building management systems (BMS), and providing users with control over all aspects of their environment.
KNX Cable Brands by Country
| Brand | Country / Region | Notes |
|---|---|---|
| Siemens | Germany (Global) | Standard bus cables, widely distributed |
| Nexans | France (Global) | CPR-compliant, LSZH, strong EU presence |
| Belden | USA / Germany (Global) | Premium shielding, used in high-end projects |
| Draka (Prysmian Group) | Italy (Global) | European standard green sheath cables |
| Ekinex | Italy (EU) | Works with their automation ecosystem |
| Datwyler | Switzerland (Global) | Flame-retardant, halogen-free cables |
| ABB | Switzerland (Global) | Supplies both devices & bus cabling |
| Schneider Electric | France (Global) | Industrial & commercial installation cables |
| Helukabel | Germany (Global) | Offers bus, hybrid, and special LSZH types |
| Kordz | Australia (Global) | Known for AV/automation cabling including KNX |
| B3 International | UK (Global exports) | Specialised in armoured & outdoor cables |
| Lapp Group | Germany (Global) | Industrial cabling, KNX LSZH options |
| LEONI | Germany (Global) | Large cable manufacturer with options |
| FS Cables | UK (Europe & MEA) | CPR-rated, LSZH bus cables |
| Opterna | USA / Middle East | Structured cabling, KNX in MEA region |
| Polycab | India (Asia) | Supplies KNX-style twisted pair bus cables |
| RR Kabel | India (Asia) | CPR-rated, KNX-style building automation cables |
| Anchor (Panasonic) | India (Asia) | Entry-level KNX-compatible wiring |
| Havells | India (Asia) | Green-sheath KNX-style bus cables, residential & commercial |
| Finolex | India (Asia) | Affordable KNX-compatible wiring solutions |
| LS Cable & System | South Korea (Asia & Global) | Strong presence in Asia, KNX-compliant |
Conclusion
KNX cables are the backbone of the bus system. It enables communication between devices in smart homes, offices, and industrial buildings. By understanding the types of cables, their specifications, and best practices for installation, you can ensure that your system runs efficiently, reliably, and with minimal interference. Whether using TP, Powerline, RF, or IP, selecting the right cable and installing it correctly is key to maximizing the benefits of KNX building automation.
Available Length -100 meters / 305 Meters /500 Meters
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