KNX Basics for Indian Residential Projects: Topology, ETS, Group Addresses and Power Supply

Short answer: design the lines, bus power supplies and address scheme before ordering. Each line needs its own supply; couplers connect lines. Physical addresses locate devices, while group addresses link functions. Changes later can require reprogramming.

This lesson focuses on wired twisted-pair KNX for homes. See the KNX reference and KNX vs Zigbee for context before quoting.

Safety first

The bus is low voltage, but actuators and controlled loads involve mains. A qualified electrician must isolate at the MCB, test dead and follow the maker’s diagram and local wiring rules. Correct bus topology does not make mains wiring safe. One cited bus-supply datasheet specifies 29 V SELV; verify the actual equipment.

What KNX is

KNX is an open standard, published as EN 50090 and ISO/IEC 14543-3. Twisted pair is common; the standard also covers powerline, RF and IP. Certified products use the same engineering tool, ETS, across manufacturers.

Sensors send telegrams; actuators perform the addressed switching, dimming or other function. Some devices do both. Standard-level interoperability does not mean identical features: check each ETS product entry before promising a function.

Topology: lines, areas and couplers

The cited coupler manual and wiring guide describe these planning limits:

Element	Role or limit
Line	Up to 64 devices including coupler in the described arrangement
Repeated line	Up to four segments of 64 using three repeaters
Power supply	Separate supply for each line and repeater segment
Cable	1000 m total in the described line arrangement; device within 350 m of supply
Main line / backbone	Up to 15 line couplers / 15 area couplers
Line coupler	Filters telegrams using ETS configuration
Repeater	Extends without filtering; both sides belong to one line
IP router	Couples through IP; relies on that network’s stability

Daisy-chain wiring is recommended; stars and spurs are allowed, loops are not. Count devices and leave growth capacity before deciding the layout. A UK integrator recommends an IP backbone for expansion without re-addressing; this is design advice, not a universal requirement.

The bus power supply

Use a KNX bus supply, not a generic adapter. Each line needs its own supply; the cited topology powers the coupler from the main line. One example supply provides 29 V, up to 640 mA, short-circuit protection and a separate auxiliary output. These are that model’s specifications.

Add the documented bus currents of the selected devices. A typical figure in the guide is about 10 mA, but panels can draw more, so device count alone is insufficient. Check ETS properties or manuals. Read instructions before using extra outputs or multiple supplies: a choke or specific wiring may be required.

Have the electrician test power loss and restoration. Confirm supply recovery and each actuator’s configured restore state in the handover.

Cable

Use the designer-specified KNX cable, commonly green and shielded. Do not substitute thinner or unshielded cable. Follow its documentation for bend radius and separation from mains; this lesson supplies no universal separation distance.

ETS: where a KNX system is actually designed

ETS means Engineering Tool Software. The practical sequence is:

1. Create the project topology: areas, lines and couplers.
2. Add devices from their manufacturers’ databases and assign physical addresses.
3. Set device parameters, including button behaviour and power-return state.
4. Create group addresses and link communication objects.
5. Download over a KNX USB/IP interface, then test with the group monitor and real devices.

Budget programming and commissioning time. Store the ETS project file and tell the client where it is; the next installer needs the design to maintain the system.

Two kinds of address

A physical address, such as 1.1.12, means area.line.device. The cited coupler manual uses area.line.0 for line couplers and area.0.0 for area couplers.

A group address, such as 1/0/10, logically connects a button’s switch object to an actuator’s switch object. The three-level structure is main/middle/sub; ETS also offers a flat view.

Choosing a group address structure

Room-based structures group floor/area, room and function, which suits residential work. Function-based structures group lighting/heating/blinds and sub-functions such as switching or feedback. Neither is a universal best choice.

Agree the structure before programming. Name addresses consistently by room, circuit and function, using clear labels such as SW, DIM or FB. Document the scheme and address list for handover.

Mistakes installers make

Avoid shared line supplies, uncounted bus current, loops, changing address schemes mid-project or missing ETS files. Decide whether KNX Data Secure/IP Secure is required during design rather than assuming it is enabled.

When KNX is the wrong tool

Wired KNX needs bus cable to devices. It suits new builds and major renovations; for a finished flat whose owner refuses wall work, consider wireless project options and the protocol overview.