What cable do I run for KNX?

KNX TP uses a single twisted-pair cable (typically J-Y(St)Y 2x2x0.8 or YCYM 2x2x0.8) carrying both data and ~30V DC bus power. One cable does both jobs.

What does a line or area coupler do?

A line coupler separates bus segments so a fault on one line cannot take down the whole system and lets each line reach its full device count; area couplers group lines into larger buildings.

How many devices fit on one KNX line?

Up to 64 physical devices per line at the standard 30V DC bus voltage; a main line plus couplers extends the system to thousands of devices across a property.

Do I need IP everywhere or just twisted pair?

Guest rooms and floors run on cheap twisted-pair; IP is used for the backbone between couplers and to reach the GRMS/PMS over the hotel network.

KNX Bus Topology & Wiring Basics for Hotels

Once you decide on KNX, the next question is physical: how is the bus actually wired across floors and rooms? This guide covers the KNX topology that hotel projects use, the couplers that keep it manageable, and how a guest-room bus reaches the GRMS over IP.

The KNX bus at a glance

KNX TP (twisted pair) is the workhorse medium. Key facts:

One cable, two jobs: a single twisted pair carries data and ~30V DC bus power to devices.
No polarity: the bus is non-polarity-sensitive, which makes termination forgiving.
Free topology: tree, line or star - within length and device limits you are not forced into one shape.

Lines, areas and couplers

A large property is organised in a hierarchy so a fault stays contained:

Level	Role
Line	Up to 64 devices on one bus segment, powered by one bus power supply.
Line coupler	Separates line segments; isolates faults and extends device count.
Area	Groups up to 15 lines under one area line.
Area coupler	Connects areas; the main line aggregates the whole building.

Device limits per line

Each line supports up to 64 physical devices at the standard 30V DC bus voltage. A main line plus couplers scales the system to thousands of devices across a property - enough for the largest hotel. Plan spare capacity per line for future additions.

Twisted pair vs IP backbone

Guest rooms and floors run on cheap twisted-pair. IP is used where distance and central management matter: between couplers, and to reach the GRMS/PMS over the hotel network. A KNX IP router is the bridge between the two worlds.

Wiring a guest room

A typical room drop includes:

A bus pair to the room control panel and thermostat.
A bus pair to the distribution-box actuators that switch lights, curtains and the fan-coil.
A short bus run to the floor IP router or line coupler.

Because logic lives in the actuators, a panel failure never darkens the room - you simply swap the panel.

Frequently asked questions

What cable do I run for KNX?: KNX TP uses a single twisted-pair cable (typically J-Y(St)Y 2x2x0.8 or YCYM 2x2x0.8) carrying both data and ~30V DC bus power. One cable does both jobs.
What does a line or area coupler do?: A line coupler separates bus segments so a fault on one line cannot take down the whole system and lets each line reach its full device count; area couplers group lines into larger buildings.
How many devices fit on one KNX line?: Up to 64 physical devices per line at the standard 30V DC bus voltage; a main line plus couplers extends the system to thousands of devices across a property.
Do I need IP everywhere or just twisted pair?: Guest rooms and floors run on cheap twisted-pair; IP is used for the backbone between couplers and to reach the GRMS/PMS over the hotel network.