The language of your installation

These are the words you will meet in your KNX paperwork. They are listed roughly from the wall inwards. The most useful one to act on is the last entry in the first group: make sure you have a copy of your project file.

Terms in your documentation

Bus

The low-voltage cable your KNX devices talk over. It is often green, and runs beside the mains wiring but separate from it. Messages are sent to a group address; line couplers pass on only the groups that need to cross lines. What it cannot do: remember. It carries messages and stores nothing.

Message on the wire (telegram)

One message on the bus. It carries who sent it, which address it is for, the kind of action (read, write or reply) and a few bytes of data. It does not say what the data means. It lasts a fraction of a second.

Group address

The numbered channel a message is sent to, written like 1/1/31. Devices send to channels and listen to channels, never to each other. That is why a KNX house can be changed without starting again. Add a second switch to a light by pointing it at the same channel.

Your house probably has several hundred. The reference home we describe on this site has 668.

Datapoint type (DPT)

The kind of value a channel is meant to carry. 1.001 is on or off. 5.001 is a percentage. 9.001 is a temperature. It is how a device knows that a few bytes mean 21.5 degrees and not just the number 21.5.

Some channels in real projects have no type set. That is common, and it does not stop the light working. It makes the project harder to read later.

The box that switches the light (actuator)

The device in your switchboard that switches or dims the load. Some switch, some dim, and some drive blind motors. They are usually mounted on a rail in the switchboard, not at the light.

Status signal (status object)

A channel where a device reports what it is really doing. This is different from the channel it listens to for commands. Without it, the system is giving commands without knowing whether they worked.

If you read one thing off your project, read which lights have this signal and which do not.

Flags

Settings that say whether an object can send, receive or be read. They are clues about whether a connection reports or commands, not proof, because they can be set wrongly. Mostly this is for your installer.

ETS

The installer’s software. Every device, channel and setting is made in it. There are cut-down versions, but most changes to what your house does need your installer, their licence, and your project file.

Project file (.knxproj)

The file ETS saves. It is a zipped set of files describing every device, channel, setting and link in the building. Treat it as something you own, not as an archive. It is often more up to date than the drawings.

Make sure you have a copy. Some owners do not. Ask your installer for one at handover. If a project is protected by a password, ask for the password too.

DALI

A separate lighting system, often joined to KNX by a gateway. Where KNX switches a whole circuit, DALI can address each light fitting. Fine scene control and automatic brightness often depend on it.

Scene

A saved set of light levels, recalled by one command. In KNX the levels are stored in the devices themselves. That is why scenes stored in the switching boxes still work if the other boxes are unplugged.

What it cannot do: change on its own. A scene is a snapshot from one day, replayed again and again. We explain why that matters in KNX in plain English.

Logic module

A KNX device that adds conditions, timers and gates. It is the closest KNX itself comes to decision-making. It looks at its own inputs. It does not look at the whole house, so two logic modules that want different things do not settle it between them.

Home server or visualisation screen

A screen or server that shows your KNX as an app or panel. Gira HomeServer, a Zennio panel, a Control4 processor or a Homey are examples. Very good for control. It shows and sends. It does not decide between clashes.

Bridge

Any device that translates between KNX and something else, such as Zigbee, Matter, Wi-Fi or voice. Good for reaching more devices. See why a bridge is not a brain.

Two terms from Casient

These are not KNX words. You will not find them in your installation paperwork.

Room behaviour

What a type of room does by default. A child’s bedroom doesn’t light by itself at night. A bathroom lights when someone is there. When two requests clash, the room’s own behaviour is checked first, and the log says why.

Decision log

A record of what ran. It shows which rule acted, what it overrode and what started it. If a system cannot tell you why it did something last Tuesday, it is hard to trust and hard to fix.

Where to go next

To see why most KNX houses still feel dumb, read KNX in plain English. Installers can find fix-it notes at KNX notes.

Send this to your installer, or ask them:

• How does the system decide between two requests?
• Can you run a free Readback on our project?

For installers

Installers: run a free Readback

Want to talk it through? Book 20 minutes with Ted.