Distribution Board Planning: Layout and Sizing According to AREI/RGIE

You plan a distribution board (consumer unit, fuse box) in four steps: count the circuits, set the protection chain, distribute the groups across rows and plan spare capacity. The AREI/RGIE, Belgium's general regulations for electrical installations, provides fixed anchor points: a main switch of at least 40 A, an RCD of at most 300 mA at the origin of the installation, then 30 mA RCDs for sockets, lighting, bathroom and laundry appliances – with no more than eight final circuits per device. This guide covers the structure, the rules and a complete example for a single-family home.

Fundamentals: structure of a distribution board

DIN rail

All modules in the board clip onto standardised DIN rails (35 mm top-hat rail to EN 60715). Each rail forms a row.

Module units (TE)

Module width is measured in TE (module units). One TE is 18 mm. Typical widths:

The data sheets of the devices you actually install are what counts.

Board sizes

Boards are sized by number of rows and TE per row:

For the single-family home in the example below, a 4-row board with 18 TE per row (72 TE) fits and leaves plenty of room for later extensions.

What the AREI requires of the enclosure

In domestic installations the board is class I or II, with a back panel that cannot be removed for its entire service life, and a door. It is made of non-combustible, non-hygroscopic material and is easily accessible without special tools (subsection 5.3.5.1, points a and c). Protective devices for circuits on different energy tariffs sit on separate plates at least 10 cm apart or in a separate board, unless the grid operator allows otherwise.

Step 1: count the circuits

List every circuit you need. The example home (3 bedrooms, 150 m², no PV) gives this list:

The maximum ratings per cross-section are in table 4.11 (subsection 4.4.1.4). Washing machine, tumble dryer, dishwasher, cooker, hob, oven and any appliance with a fixed location rated 2600 W or more get their own circuit (5.2.1.2). A socket circuit feeds at most 8 sockets (5.3.5.2 b); pure lighting circuits have no fixed point limit. More in how many sockets per circuit?.

Step 2: set the protection chain

You arrange protective devices hierarchically, from the supply downwards:

Protection hierarchy

Main switch (min. 40 A)
   └── RCD at the origin ≤ 300 mA (min. Type A, min. 40 A)
        ├── RCD 30 mA #1 (Type A)
        │    ├── MCB Lighting ground floor (B10A)
        │    ├── MCB Lighting first floor (B10A)
        │    ├── MCB Sockets living room (B16A)
        │    └── MCB Sockets hallway (B16A)
        ├── RCD 30 mA #2 (Type A)
        │    ├── MCB Sockets kitchen (B16A)
        │    ├── MCB Oven (B20A)
        │    ├── MCB Dishwasher (B16A)
        │    └── MCB Sockets bedrooms (B16A)
        └── RCD 30 mA #3 (Type A)
             ├── MCB Washing machine (B16A)
             ├── MCB Bathroom (B16A)
             ├── MCB Outdoor (B16A)
             └── MCB Garage (B16A)

With a three-phase connection (3N~400/230 V) you need a 4-pole main switch and RCD, plus multi-pole circuit breakers for three-phase outgoing circuits. The differences between Belgian network types are explained in single-phase or three-phase?.

What the AREI prescribes for the protection chain

Since version 07 of Book 1 (Royal Decree of 13 August 2026), the inspection body no longer seals the RCD at the origin from 1 November 2026; the 300 mA requirement itself stays. Details are in RCD sealing abolished.

If the earth electrode resistance exceeds 30 Ω

If the dispersion resistance of the earth electrode exceeds 30 Ω, you plan at least two RCDs of high or very high sensitivity. Each covers at most sixteen single or multiple sockets. The remaining circuits at the origin get at least one additional RCD of at most 100 mA per circuit or group of circuits (4.2.4.3 b). Reserve space for these extra devices in the first draft if the earth measurement is still pending.

RCD types

Equipment with semiconductors can produce disturbing DC components. Subsection 5.3.5.3, point f, lists several permitted solutions, including an RCD that keeps working with such faults or a DC fault-current detector installed in coordination with the RCD.

Selectivity

You demonstrate selectivity between upstream and downstream RCDs from sensitivity, time-current characteristics, manufacturer coordination data and the complete protection concept. A time-delayed device can be part of the solution; on its own it does not guarantee selectivity.

Step 3: distribute the groups across rows

AREI rule: at most 8 final circuits per 30 mA RCD

Under subsection 4.2.4.3 b you connect at most eight final circuits to an RCD of high or very high sensitivity. Four to six circuits per device leaves headroom for later extensions.

Typical row allocation

Step 4: plan spare capacity

Plan free positions; 20 to 30% of the TE is proven practice, not an AREI requirement. With 20 circuit breakers that means at least four to six free TE. Close empty positions with blanking plates.

You need spare capacity for:

• future loads such as an EV charger, air conditioning or a sauna,
• redistribution when an RCD carries too many circuits,
• avoiding a later board replacement.

Spare capacity is more than free TE: also plan free terminals, enough trunking, accessible N and PE bars, room for measurements and a documented direction of extension.

Example: 4-row board for a single-family home

A complete example for a Belgian single-family home (3 bedrooms, 150 m², single-phase, no PV):

Row 1 — Supply and protection (18 TE)

Row 2 — Group 1: lighting and living area (18 TE)

Row 3 — Group 2: kitchen and bedrooms (18 TE)

Row 4 — Group 3: bathroom, outdoor, utility (18 TE)

Total: 18 circuit breakers (compact 1P+N), 4 RCDs, SPD, main switch and bell transformer = 34 of 72 TE used, 53% spare. Each 30 mA RCD carries six final circuits and stays below the limit of eight. The hob and a future EV charger fit in the spare positions.

Common mistakes in board planning

Labelling and documentation

Subsection 3.1.3.1 requires control, protective and isolating devices to be labelled clearly, conspicuously and indelibly. The board itself carries its own identifier and the supply voltage (3.1.3.3). Label each protective device with:

• the circuit identifier, identical to the single-line diagram and situation plan (on the single-line diagram a capital letter identifies the circuit, 3.1.2.1),
• the function, for example “Lighting ground floor” or “Sockets kitchen”,
• optionally the room or floor.

Use a label strip or stick the overview inside the door; most manufacturers supply writable inserts.

From a layout sketch to an executable design

Counting modules is the spatial starting point. Before ordering, the electrician checks the connection data, earthing system, prospective short-circuit current, selectivity or back-up protection and the manufacturer approvals for combined devices. You therefore never copy rated current, breaking capacity or cross-section from an example without checking. Power dissipation in the closed enclosure, ambient temperature, ventilation and permitted terminal loading also shape the choice.

Work row by row. Record supply, main isolation, residual-current protection and surge protection as a traceable protection chain. Then arrange the final circuits, but do not mistake a visually tidy row for electrical selectivity. With PV, a battery, a generator or charging infrastructure, show clearly from which direction energy can flow and which parts may remain energised with the grid switched off. Manufacturer documents for the RCD, SPD, inverter or EV charger are binding design inputs.

Before export you align three levels: the physical occupancy of the board, the protection chain in the single-line diagram and the circuit identifiers on the situation plan show the same state. Book 1 V06 requires schemas, plans and documents to carry an unambiguous number, version and version date (section 3.1.2). For domestic installations, the name, capacity and VAT number (if applicable) of the person responsible and the installation address also appear on the single-line diagram and situation plan (3.1.2.1 a).

Board handover record

Before closing the cover, record for every outgoing circuit its identifier, purpose, number of poles, protective device, rated current, cable data and associated RCD. For controllable loads, add contactor, control circuit and manual operation. For multi-phase outgoing circuits, document the phases used; for single-phase circuits, a phase list helps you spot later imbalance. Check that each neutral is assigned to the correct RCD and that protective-conductor terminals stay accessible.

A photo complements the structured data but does not replace it. Terminal markings match the diagram and the label strip. Only record tightening torques or thermal follow-up checks when they come from manufacturer instructions or an execution record.

Also check mechanical accessibility: covers can still be fitted, conductors do not run in front of operating devices and measuring points remain reachable. Record separate N bars, links and supplies traceably. A spare position without a safe connection option is not usable spare capacity.

Keep the approved PDF together with the inspection report, measurement records and relevant data sheets in the installation file. When you extend later, do not overwrite the old file: increase the version, set a new version date and describe the change. That keeps it traceable which drawing showed the real board at which inspection.

Planning the board in PlanElec

In the PlanElec Board Editor you place modules on DIN rails, automatically or by hand; enclosure suggestions take recorded module widths, spare capacity and accessories into account. For existing installations, PlanElec recognises visible DIN modules in photos and turns them into a layout proposal you review. The AREI/RGIE self-check flags, among other things, an overfilled board, more than eight final circuits on a 30 mA RCD, a missing RCD at the origin, a main switch or main RCD below 40 A and socket circuits without 30 mA protection; less than 20% spare capacity appears as a tip. Measurements, manufacturer evidence and the inspection by the recognised inspection body remain separate steps. The rules covered are listed in what the self-check verifies.

Official basis

• FPS Economy: RGIE/AREI, Book 1
• Book 1 V06: sections 3.1.2 and 3.1.3 (schemas, plans, labelling), subsections 4.2.4.3, 4.4.1.4, 5.2.1.2, 5.3.5.1 to 5.3.5.3; sealing abolished by version 07 from 01.11.2026.

Related articles

• Creating a single-line diagram
• Do I need a 30 mA RCD for every socket?
• Cable cross-section and breaker: the right combination
• PV system in the diagram

Plan your board in the PlanElec Board Editor and check it yourself →