Home Automation and KNX in the Electrical Installation: What Belongs on the Plan and the Single-Line Diagram?
A bus instead of strapping conductors: what a KNX installation shows on the single-line diagram and situation plan, what belongs in ETS and how PlanElec keeps the two apart – with the AREI/RGIE reference beside each statement.
AuthorStephan BehmWhat does a KNX installation have to show on the single-line diagram and the situation plan?
The inspection file covers the electrical installation: the bus power supply as a fixed appliance in the board together with its overcurrent protection, the KNX actuator as a control unit, every switched load circuit with its type, cross-section, number of conductors and installation method, and every push-button as a control unit with its reference. What does not belong there: group addresses, device parameters, scenes and logic. Those live in the ETS project and are not a matter for the AREI/RGIE.
That dividing line is the whole article in one sentence. The rest explains why it runs there and what sits on each side.
| Element | What it is electrically | On the single-line diagram | On the situation plan | In the ETS project |
|---|---|---|---|---|
| KNX bus power supply | fixed appliance, a 230 V load in the board | yes, with its upstream overcurrent protective device (3.1.2.2 a) | at the location of the distribution board (3.1.2.3 a) | as a device on the line |
| Bus cable between bus devices | extra-low-voltage line (5.2.2.2, 5.2.9.15) | not among the mandatory data listed in 3.1.2.2 a for the load-circuit wiring | no | line and area topology |
| KNX actuator in the board | control device under 5.3.3.2 b and switching element | yes, as a fixed appliance in the load circuit | at the location of the board (3.1.2.3 a) | yes, with application and parameters |
| Actuator channel → luminaire | 230 V load circuit | yes: type, cross-section, number of conductors, installation method; light point numbered (3.1.2.1 a) | light point with circuit letter and number (3.1.2.1 a) | communication object of the channel |
| Push-button / control point | control unit on the bus, with no load circuit of its own | yes, as a control unit with a sequential number (3.1.2.1 a) | circuit letter plus the number of the light point it controls (3.1.2.1 a) | group address |
| Group addresses, parameters, scenes | not electrical equipment | no | no | yes — and there only |
What does domotica or building automation mean?
Domotica is the usual Belgian term for automating a dwelling: operating, switching, controlling and linking lighting, shutters, heating and access through one shared control layer instead of one hard-wired switch per function. "Building automation" means the same thing one size up, in non-domestic work.
The AREI/RGIE knows the term — not as a regulatory category of its own with its own duties, but as a symbol family. Table 2.23, part of Chapter 2.13, lists the control unit under letter J, "Domotics". It is "represented by a rectangle consisting of two parts": the lower part carries the basic symbol — the table gives a switch or a socket outlet with a switch as examples — and the upper part the type of control.
Two things follow. First, a home-automation control point is, in drawing terms, a control unit, not a plain switch — and Sub-section 3.1.2.1 point a expressly requires control units to be numbered alongside light points and socket outlets. Second, the regulation prescribes no KNX-specific symbol. Where Table 2.23 contains none, the same sub-section allows "any other clearly identifiable symbol defined in the legend of the single-line diagrams and situation plans". On a bus installation the legend is therefore not optional decoration.
What is KNX and how does it differ from a conventional installation?
KNX is a manufacturer-independent standard for building automation. The KNX Association lists the approvals: ISO/IEC approved KNX in 2006 as the International Standard ISO/IEC 14543-3, CENELEC in 2003 as the European Standard EN 50090, CEN in 2006 as EN 13321-1 (a mere reference to EN 50090) and EN 13321-2 (KNXnet/IP), SAC in 2007 as the Chinese Standard GB/T 20965, and ANSI/ASHRAE in 2005 as the US Standard ANSI/ASHRAE 135. That is exactly what separates KNX from a system bus defined by a single manufacturer: the standard belongs to no brand.
Bus devices exchange information over one shared medium — in the KNX Association's words, "twisted pair, radio frequency, power line or IP/Ethernet". The information to be transmitted is "packed in a telegram" and sent from a sensor to actuators. In Belgian housing the twisted pair is the norm; the other media are mainly retrofit and coupling routes.
| Aspect | Conventional installation | KNX installation |
|---|---|---|
| What the control point does | interrupts the load circuit itself, 230 V is present at the switch | puts a telegram on the bus; the actuator channel in the board switches the 230 V |
| Wiring to the control point | load wiring, conductor count depending on the switching arrangement | bus cable at extra-low voltage |
| Additional control point | one more intermediate switch plus two strapping conductors per section | one more push-button on the existing bus, assigned in ETS |
| Changing a function after handover | rewiring | reparameterising in ETS, the wiring stays |
| Where the function lives | in the wiring | decentralised, in sensor and actuator, not in a central unit |
| Inspection documents | single-line diagram and situation plan (3.1.2.2 a, 3.1.2.3 a) | the same documents with the same mandatory content, plus the ETS project as separate documentation the regulation does not govern |
| Commissioning | energise and check | additionally addressing and programming with ETS |
| Fault finding | measurement in the load circuit | measurement in the load circuit and bus diagnostics |
| Dependence on the planning tool | none | changes require the ETS project and access to it |
What are the roles of bus power supply, sensor, push-button, actuator, channel and load?
One chain makes it clearest. A ceiling light in the hallway is to be operated from a push-button beside the front door.
- Bus power supply. A module in the board is fed from a 230 V circuit and provides the operating voltage for all bus devices at its BUS+ and BUS− terminals. It is a fixed appliance and, like any other, needs an upstream overcurrent protective device. Without it the bus is dead and no push-button works — including the one in the hallway.
- Push-button as sensor. The push-button hangs on the bus, not on the load circuit. Pressing it produces a telegram that the push-button places on the bus. It carries no load current.
- Telegram. The telegram is addressed to a group address, not to a cable. Every device listening to that address receives it at the same time.
- Actuator channel. The switch actuator in the board has several channels. Precisely the channel whose communication object is linked to that group address closes its relay.
- Load circuit and load. Only here does current flow: from the overcurrent protective device, through the actuator channel, along the wiring to the luminaire. This part is an entirely ordinary electrical installation, sized, protected and documented by the ordinary rules.
The actuator channel is therefore the control device within the meaning of Sub-section 5.3.3.2. Point b expressly permits, at extra-low and low voltage, contactors, control auxiliaries and "electronic devices" alongside switches and circuit-breakers, provided they comply with "the relevant standards approved by the King or registered by the NBN, or with provisions ensuring at least an equivalent level of safety". A KNX actuator is thus no exotic construction — but neither is it a free pass: the product's compliance with those standards remains a condition.
Point d of the same sub-section expressly allows one device to control several machines or appliances running simultaneously. A channel switching four spots of the same group is covered. The same point also makes clear that a control device is required even where the appliance's operation depends on a relay, a thermostat or a similar component — automation does not replace the control device, it is one.
What is supplied at 230 V and what communicates over the bus?
The split runs at the actuator's terminals, not along device categories.
Carrying 230 V: the supply to the bus power supply, the supply to the actuator, every switched outgoing circuit from an actuator channel to a luminaire or shutter motor, and everything already wired conventionally.
Running on the bus: push-buttons, presence and brightness sensors, room controllers, displays, and communication between actuators.
The bus cable is an extra-low-voltage line. Its installation is governed by Sub-section 5.2.2.2: all installation methods for low-voltage wiring apply to extra-low-voltage wiring as well, "with relaxations regarding the electrical and/or mechanical properties", except under external influences BE2, BE3 or CA2. Sub-section 5.2.9.15 point b confirms this for ELV installations and names the few provisions from Section 5.2.9 that do not apply there. Whether the particular bus power supply delivers safety extra-low voltage — bringing Sub-section 5.2.2.3 into play as well — is stated in the manufacturer's data sheet. That is a property of the product, not a property of "KNX".
Two further points of Sub-section 5.3.3.2 sit exactly on this boundary:
- Point c: except for measuring purposes, single-pole control devices are not fitted in neutral conductors. A single-pole switching channel belongs in the line conductor, not the neutral — the command coming from software changes nothing about that.
- Point f: control circuits are designed and arranged so as to limit risks arising from accidental contact of one or more points of the control circuit with the body or with earth, which could cause unintended starting or prevent the shutdown of the controlled machine or appliance. The bus is a control circuit in exactly that sense.
What does the inspection need, and what belongs to the ETS project?
The approved inspection body checks the electrical installation against the documents the regulation prescribes. KNX does not change that list.
Under Sub-section 3.1.2.2 point a the single-line diagram states at least: the characteristics of the electrical wiring (type, cross-section, number of conductors), the installation methods, the type and characteristics of the residual current protective devices, the type and characteristics of the overcurrent protective devices, the switches, the connection boxes, the junction boxes, the socket outlets, the light points, the fixed machines and appliances, and the sources. Bus power supply and actuator are fixed appliances and fall under the same item as any other board module.
Under Sub-section 3.1.2.3 point a the situation plan indicates the location of the distribution boards, connection and junction boxes, socket outlets, light points, switches, fixed machines and appliances, and sources shown on the single-line diagram.
The referencing required by Sub-section 3.1.2.1 point a is where sloppiness on a bus installation shows up fastest. On the single-line diagram each elementary circuit is identified by a capital letter; each light point, each socket outlet and each control unit receives a number "giving the order in which these elements occur in the elementary circuit, starting from the overcurrent protective device upstream of the circuit". On the situation plan, "each switch and each control unit is identified by the letter of the circuit in which it is located and by the sequential number of the light point or appliance it controls". A KNX push-button is such a control unit — the assignment "this button operates that light point" is therefore a fact of the inspection file, not only a fact of ETS.
Under Sub-section 3.1.2.1 point d, diagrams, plans and documents are kept up to date and made available on site to everyone authorised to supervise, inspect, maintain, repair or alter the installation. Whoever later changes an assignment in ETS updates the plan with it.
ETS, by contrast, holds: individual addresses, group addresses, application programs, parameters, scenes, time and logic functions, the line and area topology, and the project backup. None of that appears in the regulation, and none of it replaces something the regulation requires. The converse is equally true: a tidy ETS project is not a single-line diagram.
When is KNX worthwhile, and what extra effort does it bring?
This section is trade practice, not regulation — the AREI/RGIE says nothing on the matter.
KNX pays off where the number of control points, links or later changes is high: many control points for the same light, shutter control across whole façades, linking shading, heating and presence, uses that change over the years. From three or four control points onward the wiring effort of an intermediate-switch arrangement grows quickly; the conventional alternatives — push-buttons with an impulse relay — are described in Two-way, intermediate or double switch and remain the cheaper answer for many single-family homes.
The extra effort is real and lands in three places:
- Design. The bus cable route, board space for supply and actuators, spare channels, and a channel naming scheme that still reads clearly in five years.
- Commissioning. ETS licence, project work, addressing, programming and functional testing. That is a service in its own right with its own time budget, not a by-product of the wiring.
- Handover and operation. The ETS project belongs to the client and should be handed over. Without the project file and without someone holding ETS access, every later change becomes expensive.
The most common miscalculation is not the material price but the assumption that programming is finished once the wiring is.
How does KNX differ from proprietary systems, Matter, Home Assistant and wireless retrofits?
| System | What it is | Where the function lives | What of it belongs in the electrical file |
|---|---|---|---|
| KNX | manufacturer-independent standard (EN 50090, EN 13321-1, ISO/IEC 14543-3) | decentralised, in sensor and actuator | bus power supply, actuator and all switched load circuits |
| Proprietary bus of one manufacturer | one supplier's system world, often technically similar but without a manufacturer-independent standard | manufacturer-dependent | the same equipment as with KNX; the symbol must be defined in the legend |
| Matter | IP-based connectivity protocol of the Connectivity Standards Alliance; runs on Wi-Fi and Thread, with Bluetooth Low Energy used for commissioning | in the device and the control app | only the fixed installation behind it; the device itself is usually plug-in |
| Home Assistant | open-source software on a server that brings existing systems — KNX included — together | in the software | nothing of its own; the server is an ordinary load |
| Wireless module behind the switch | relay module in the wall box, radio-controlled | in the module and the app | appears once the fixed wiring is altered for it |
For the inspection the decisive distinction is not "smart or not" but fixed or not. A plug-in adapter changes nothing about the fixed installation. A DIN-rail module in the board and an actuator switching a lighting circuit are part of the fixed installation. The boundary for Wi-Fi modules, smart sockets and smart lamps is covered in Smart home and AREI; this article stays with the wired bus.
Matter and KNX are not mutually exclusive, incidentally. Matter standardises how IP devices and apps understand each other, KNX the fixed automation in the building; in practice they meet in a gateway, not on the same cable.
Can PlanElec replace ETS?
No, and that is not its job. PlanElec documents the electrical installation together with the planned automation functions. ETS configures, addresses and programs the KNX devices. These are two work steps with two results, and you need both.
| Task | PlanElec | ETS |
|---|---|---|
| Single-line diagram and situation plan with bus power supply, actuator, load circuits and push buttons | yes | no |
| Channel assignment: which channel switches which load, which button operates it | yes (planning) | yes (programming) |
| Logical bus lines with supply and bus current budget | yes (planning) | yes |
| Terminal plan and board-door sheet | yes | no |
| Physical addresses and group addresses | no | yes |
| Communication objects, parameters, scenes and logic | no | yes |
Programming, live bus diagnostics, .knxproj files | no | yes |
Whoever commissions a KNX installation needs ETS. Whoever presents it for inspection needs a single-line diagram and a situation plan. PlanElec delivers that second half and keeps it consistent with the channel planning.
How do you document a KNX installation in PlanElec?
Open the project metadata and choose the KNX profile under Building automation. That gives you the manufacturer-neutral board modules KNX power supply and KNX actuator, and on the floor plan you place push buttons from Control points & sensors. You configure the bus power supply by its bus current, 320 mA or 640 mA. The actuator gets a function (switching or blind), a channel count (4, 8, 12 or 16) and a rated current per channel (6, 10 or 16 A).
In the Smart home area, you assign each channel its loads and control points; one push button can operate several channels, and several push buttons can share one channel. Under Lines, you assign modules and control points to the planned bus lines and choose the line's power supply. PlanElec shows known bus currents and unknown contributions separately. The single-line diagram shows the supply and the actuator once each; for every occupied channel, it shows an OUT power line to the load and a separate KNX IN line to the control point. You locate the push button on the situation plan with the push-button symbol.
Under Export → Domotica, you produce the channel plan, terminal plan, function list per room, topology diagram, home-automation bill of quantities and the self-check report, individually or bundled as a home-automation handover dossier. The draft carries a watermark and can be exported with open data. For the final version, PlanElec checks that a protected bus power supply exists, that the actuators sit behind a circuit breaker or RCBO, that assigned loads have a power rating, that no consumer is assigned twice, that no channel would be overloaded and that a load marked as KNX-controlled actually has a channel. A push button without a channel assignment remains a warning and does not block.
Lighting circuits and blind motors are supported. The illustrated step-by-step guide is in the knowledge base: Plan and document KNX.
What does the AREI/RGIE self-check cover for KNX?
The self-check is advisory and evaluates the supported rules from your project data. For automation installations, two checks are added:
- Channel load: it compares the current sum of the documented load ratings with the channel's rated current (protection objective under Sub-section 4.4.1.1). If a rating is missing, it reports a data gap rather than a pass.
- Known bus current: it compares the known device currents on a line with the supply's capacity and warns when it is exceeded. Unknown contributions stay marked as open.
The rest of the bus planning you check against the manufacturer documentation:
- Control logic: whether a push button is assigned to the right channel is your planning decision; electrically, even a wrong assignment is flawless.
- Bus cable: routing, run length and number of devices per line are in the manufacturer documentation.
- Product conformity: whether actuator and supply meet the standards required by Sub-section 5.3.3.2 point b is a property of the product, not of the drawing.
- ETS data: parameterisation and cybersecurity of the installation belong to the ETS configuration.
The conformity inspection of the installed work, including its measurements, is carried out by the approved body.
Related guidance
- Smart home and AREI
- Two-way, intermediate or double switch on the single-line diagram
- Creating a single-line diagram step by step
- Drawing a situation plan
- AREI electrical symbols overview
Build your KNX documentation in PlanElec →
Basis: AREI/RGIE Book 1 V06 — Chapter 2.13 with Table 2.23 letter J, Sub-sections 3.1.2.1, 3.1.2.2, 3.1.2.3, 4.4.1.1, 5.2.2.2, 5.2.2.3, 5.2.9.15 and 5.3.3.2. Checked on 5 October 2026. KNX figures per the KNX Association's own publications (standardisation, technology). The official text, the actual installed state and the approved body's inspection remain decisive.