What is a single-line diagram?
A single-line diagram is a simplified drawing of an electrical installation in which each cable is shown as one line, regardless of the number of conductors it contains. That is where the name comes from. It starts at the meter and shows what follows: the distribution board, RCDs, circuit breakers and, for each circuit, the cable and what is connected to it.
Think of it as the identity card for your installation. If you read the schematic, you will know how your home is electrically assembled without opening a single wall: how many circles there are, how heavily each circle is secured, what cable section is used and which devices hang on it. For an electrician looking for a breaker, or to replace a circle, that's gold. For the judge it is simply a requirement.
In addition to the single-line diagram, there is a second mandatory document: electrical layout diagram. This shows on the ground plan of your home where every socket, light point and every switch is located. Both schemes belong together: the numbering on one must correspond to the numbering on the other.
How do you read a single-line diagram?
A single-line diagram can be read from top to bottom, in the direction of the current. At the top you will find the connection and the counter, below which the installation branches out circle by circuit. The most important elements are recognized by their symbol:
- The residual current device (RCD): The power loss switch that protects you from electrocution. The schedule shows his sensitivity, for example 300 mA for the general and 30 mA for wet areas.
- The circuit breakers: the fuses that protect each circuit from overload. The diagram indicates their calibre, for example 16 A or 20 A.
- The cables: per circle the type and section, for example XVB 3G2,5. That tells how many conductors there are and how fat they are.
- Consumers: sockets, light points, switches and fixed devices such as an oven, boiler or EV charger, each with their own symbol and number.
Those numbers are not a detail. Each circle and each terminal point will receive a number that you will find on the installation layout plan. So anyone, from judge to electrician, can find any point on the drawing in your home.
Why is it mandatory at the inspection?
The AREI, the regulation to which every electrical installation in Belgium must comply, requires a single-line diagram and an installation layout plan at each inspection. So with a new installation, after an important change like a new distribution board, and to the electrical inspection when selling from your apartment.
The judge uses the schematic as a guide: he checks if what is on paper matches what is in your plate and behind your walls. If the schematic is missing, he will not be able to do that check and your installation will be rejected, no matter how well she is put together. An approved schema is stamped by the examiner and then belongs to your home: keep it with the board and give it to sales.
Rule of thumb: an installation without schematics is an installation that is not verifiable for the examiner. The paperwork is therefore not a side issue, it is an inspection requirement.
What if the schedule doesn't match reality?
A scheme that is there but no longer correct is almost as problematic as no schedule. That happens faster than you think: a kitchen that has been rebuilt, a circle that has been added to an EV charger, an attic that became a desk. Any change to your installation should also end up on the schematics, update the so-called as-build.
If the judge determines a difference between schedule and reality, he notes that as an infringement in the inspection report. What you do, you read in us Roadmap after a disapproval. Usually, the solution is simple: have the schematic redesigned on the basis of the installation as it stands today.
Frequently asked questions about the single-line diagram
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What is the difference between a single-line diagram and an installation layout plan?
The single-line diagram shows the installation's structure: distribution board, RCDs, circuit breakers, circuits and cables. The layout diagram shows where everything is on the floor plan: each socket, light point and switch. Both are required for the inspection and use the same numbering.
Is a single-line diagram mandatory?
Yes. The AREI requires a single-line diagram and an installation layout plan at every inspection: with a new installation, after a major change and when selling your property. Without schematics, the installation will be rejected.
Can I draw my single-line diagram myself?
That's allowed. There's no obligation to let a professional do it. But the schedule must be complete and correct, with the right symbols, cable sections and numbering. Errors or missing circles lead to comments on the inspection. If you doubt, then having it measured and drawn is the safest way.
My single-line diagram doesn't add up after a remodel. What now?
Then you have it updated into an as-build schematic: a scheme that shows the installation as it really is today. We measure the changes, adjust both schedules and deliver them digitally, so that the next inspection goes smoothly.
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What applies to your situation?
Equipment selection, price, scheduling and any conditions will be confirmed for your project. This information does not replace an assessment of your installation or an individual quote.
Wattra does not carry out official inspections. We can organise a check at a recognized inspection body and discuss the preparation or necessary adjustments, including for installations of other performers.