What Is a KNX/EIB Bus Cable? Types and Selection Criteria

An EIB-BUS (KNX) cable is a twisted-pair, foil-screened communication cable that links KNX sensors and actuators and carries both data and bus power.

An EIB-BUS cable (KNX cable) is a twisted-pair, foil-screened communication cable that connects sensors, push-buttons and actuators in the KNX building automation system, the successor of EIB. In homes, hotels and offices it carries both data and the devices' bus power over the same pair for lighting, blind and HVAC automation.

Types

• By number of pairs: 1x2x0.8 mm has one pair. In 2x2x0.8 mm the first pair (red/black) is for the bus line and the second pair (white/yellow) is kept as a spare or used for a second bus line or an additional SELV supply; mains voltage is never put on this pair.
• By insulation and sheath: In type 2Y(St)H the core insulation is PE and the sheath is halogen-free (Mekas). In type H(St)H both insulation and sheath are halogen-free (Erse). Reçber products have an LSZH sheath and the 2M Kablo product a YCYM-HFFR sheath. (St) denotes the aluminium foil screen.
• By reaction-to-fire class: Types stated as CPR class B2ca-s1a,d1,a1 are for projects that require a high fire class.

Cables in the catalog

0.8 mm is the core diameter; +0.4 mm is the drain wire that runs with the screen. The cables are sold by the metre.

Selection criteria

1. KNX suitability: Choose a bus cable that the manufacturer states is suitable for the KNX line.
2. Number of pairs: If you need a spare pair or a second line later, take 2x2x0.8 mm.
3. Reaction-to-fire class: Choose a cable in the CPR class required by the building's fire regulations and the project specification.
4. Line length: On a KNX TP line, the total cable length in one line must not exceed 1000 m, the distance between the power supply and a device 350 m, and between two devices 700 m.
5. Installation: The minimum bending radius in the product data is 10 × cable diameter.

Common mistakes

• Reversing polarity: On the KNX line the red core is connected to (+) and the black core to (−).
• Taking 0.8 mm for the cross-section: 0.8 mm is the core diameter; the cross-section is about 0.5 mm².
• Putting mains voltage on the second pair: A bus cable is a low-voltage communication cable; it does not carry mains circuits.
• Using another communication cable instead: Profibus cables or network cables are for other systems with a different impedance and construction; they do not replace a KNX cable.

Related standards

• EN 50090: The home and building electronic systems standard series on which KNX is also based.
• EN 50290-2-27: Standard for the halogen-free (HFFR) sheath material given in the product data.
• EN 13501-6: Reaction-to-fire classification of cables; B2ca, s1a, d1 and a1 are given to this standard.

Brands in the catalog

The EIB-BUS Cables category has 9 active products: Reçber Kablo 4, Mekas Kablo 2, Erse Kablo 2, 2M Kablo 1. Other bus and signal cables are in the Industrial and Communication Cables category.

Frequently asked questions

Are KNX cable and EIB-BUS cable the same?

Yes. EIB is the predecessor of KNX; the screened 2x2x0.8 mm or 1x2x0.8 mm bus cable used on a KNX TP line is sold under both names.

Which cores are used in a KNX cable?

The bus line is connected to the first pair: red (+), black (−). The second pair (white/yellow) is kept as a spare.

What does B2ca-s1a,d1,a1 mean?

It is a CPR reaction-to-fire class. B2ca gives the flame spread and heat release class, s1a low smoke density, d1 limited flaming droplets and a1 low acidity.

How long can a KNX line be?

The total cable length in one line must not exceed 1000 m. In larger installations a new line is added with a line coupler.