The ABB LK/S 4.2 KNX Line Coupler is a modular installation device (MDRC) for structuring medium and large ABB i-bus® KNX installations. Occupying 2 modular spacings (2 MW), it connects a KNX line to a main line, a main line to an area line, or acts as a repeater — always providing electrical isolation between coupled segments.

The LK/S 4.2 supports KNX Data Secure telegrams (processed, filtered, forwarded, or blocked per configuration), long frames (from ETS 5 onwards), and configurable group-address filtering — including main groups 14…31 with ETS 4. With just 0.3 W power loss, it is one of the most efficient infrastructure devices in the KNX panel.

Key Features — Topology, Filtering, and Data Secure

Coupler Modes

• Line coupler: Connects a line to a main line within an area.
• Area coupler: Connects a main line to an area line between areas.
• Repeater: Extends TP segment reach while maintaining galvanic isolation.
• Electrical isolation: Galvanic separation between coupled bus segments.

Filtering and Security

• Group-address filtering: Configurable filter table to reduce unnecessary inter-segment traffic.
• KNX Data Secure: Secure telegrams processed according to filter and security settings.
• Long frame support: Compatible with extended telegrams from ETS 5 onwards.
• Low power: 0.3 W typical power loss.

At a Glance

Specification	Detail
Product type	KNX Line / Area Coupler and Repeater
Order code	LK/S 4.2 (2CDG110171R0011)
Coupler modes	Line coupler, area coupler, repeater
Data Secure	KNX Data Secure telegrams supported
Long frames	Supported (ETS 5+)
Filtering	Main groups 14…31 (ETS 4); extended with ETS 5
Power loss	0.3 W
Dimensions (W × H × D)	36 × 90 × 64.5 mm (2 MW)
Protection	IP20
Bus system	KNX twisted pair (TP)

Full electrical ratings, ordering codes, and classification data are listed under Technical Specifications. Technical data, product manual, installation instructions, ETS application, CAD, and EPLAN data are under Downloads.

Applications and KNX Integration

• Large residential and commercial: Segment lines by floor or functional zone to limit bus traffic and fault propagation.
• Multi-area campuses: Use as area coupler between main lines when IP routing is not required between every segment.
• Secure installations: Forward or block KNX Data Secure telegrams at segment boundaries per security concept.
• ETS configuration: Import the official .knxprod application (Downloads), assign coupler role, and configure filter table for each main group.
• Panel power: Requires a KNX bus power supply on each coupled segment — plan capacity with an ABB supply such as the SV/S 30.320.1.1 KNX Power Supply 320 mA per line.

Choosing Line Couplers and IP Routers

When KNX segments must be linked over Ethernet, choose the IPR/S3.1.1 KNX IP Router for standard KNXnet/IP, or the IPR/S3.5.1 KNX IP Router Secure for encrypted KNXnet/IP Secure backbone communication. The LK/S 4.2 remains the standard choice for TP-side line and area coupling within the distribution board.