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

The distribution board (also called consumer unit, fuse box, or electrical panel) is the heart of every electrical installation. This is where all circuits converge, where the protection devices sit that protect your home and family from electrical hazards. Thoughtful planning not only saves money but also prevents problems during the AREI/RGIE inspection.

Fundamentals: Structure of a Distribution Board

DIN Rail (Omega Rail)

All modules in the board are snapped onto standardised DIN rails (35 mm omega rail per EN 60715). Each rail forms a row in the board.

Module Units (TE Units)

Module width is measured in TE (Teilungseinheiten / division units). One TE equals 18 mm. Typical widths:

Board Sizes

Boards are sized by rows and TE per row:

For a typical single-family home, we recommend at least a 4-row board with 18 TE per row (72 TE total).

Step 1: Count Your Circuits

List all required circuits. For an average single-family home (3 bedrooms, 150 m²):

Tip: Maximum 8 single or multiple socket outlets per final circuit (AREI Art. 5.3.5.2b). Lighting circuits may have more points, but in practice max. 8 luminaires per circuit is recommended.

Step 2: Choose Protection Devices

Protection devices are arranged hierarchically — from the supply (top) downward:

Protection Hierarchy

Main switch (40A or 63A)
   └── Main RCD 300 mA (Type A-S, selective)
        ├── Group 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)
        ├── Group RCD 30 mA #2 (Type A)
        │    ├── MCB Sockets kitchen (B16A)
        │    ├── MCB Oven (B20A)
        │    ├── MCB Dishwasher (B16A)
        │    └── MCB Sockets bedrooms (B16A)
        └── Group RCD 30 mA #3 (Type A)
             ├── MCB Washing machine (B16A)
             ├── MCB Bathroom (B16A)
             ├── MCB Outdoor (B16A)
             └── MCB Garage (B16A)

RCD Types

Selectivity

Selectivity does not mean that the upstream RCD “observes” whether a group RCD responded. It must be demonstrated from sensitivity, time-current characteristics, manufacturer coordination and the complete protection concept. A time-delayed device can form part of that design but cannot alone guarantee selectivity or that only the affected group RCD will trip.

Step 3: Allocate to Rows

AREI Rule: Max. 8 Final Circuits per RCD

According to AREI Art. 4.2.4.3b, a maximum of 8 final circuits may be connected downstream of one residual current device (RCD). In practice, 4–6 circuits per RCD are recommended for comfortable reserve.

Typical Row Allocation

Step 4: Plan Reserve Spaces

Plan at least 20% reserve spaces — ideally 30%. This means:

• With 20 required MCBs → at least 4–6 free TE spaces.
• Empty spaces are closed with blanking plates.

Why?

• Future additions (EV charger, air conditioning, sauna).
• Redistribution if an RCD has too many circuits.
• Avoiding an expensive board replacement.

Example Layout: 4-Row Board for a Single-Family Home

Here is a complete example for a typical Belgian single-family home (3 BR, 150 m², no PV):

Row 1 — Supply & Protection (18 TE)

Row 2 — Group 1: Lighting + Living Area (18 TE)

Row 3 — Group 2: Kitchen + Bedrooms (18 TE)

Row 4 — Group 3: Bathroom, Outdoor, Utility (18 TE)

Total: 18 MCBs + 4 RCDs + SPD + main switch + bell transformer = 34 TE occupied out of 72 TE → 53% reserve

Common Mistakes in Board Planning

Labelling and Documentation

Every MCB must be labelled with:

• Circuit number (identical to single-line diagram and situation plan)
• Function (e.g., "Lighting GF", "Kitchen sockets")
• Optional: room or floor

Apply the label inside the board cover or use a labelling strip. Most board manufacturers supply writable inserts.

From a layout sketch to an executable design

Counting module spaces is only the spatial starting point. Before ordering, the electrician must verify the connection data, earthing system, prospective short-circuit current, selectivity or backup behaviour, and the manufacturers' conditions for the combined devices. A rated current, breaking capacity or conductor size must not be copied from an example house. Heat dissipation inside the enclosure, ambient temperature, ventilation and permitted terminal loading also affect the final selection.

Review the board row by row. Record the supply, main isolation, residual-current protection and surge protection as one traceable protection chain. Then allocate the final circuits, while remembering that a tidy row does not prove electrical selectivity. With PV, a generator, storage or charging equipment, the drawing should also make possible directions of energy flow and parts that may remain energised understandable. Instructions for the exact RCD, SPD, inverter or charger remain inputs to professional design.

Reserve planning is wider than spare module units. Consider spare terminals, usable wiring ducts, accessible neutral and PE bars, measurement access and a documented direction for later expansion. There is no universal AREI/RGIE spare percentage. The appropriate margin depends on foreseeable loads, enclosure limits and the available connection capacity.

Before export, compare three layers: the physical board population, the protection chain in the single-line diagram, and the circuit references on the situation plan must describe the same as-built state. Book 1 V06 requires an unambiguous number, revision and revision date on diagrams and documents. Domestic plans also carry the installation address and details of the person responsible for the work. A PlanElec self-check may expose modelled gaps, but it cannot supply measurements, manufacturer evidence or the decision of an approved control body.

Official basis

Board handover record

Before closing the cover, record for every outgoing circuit its identifier, purpose, pole count, protective device, rating, conductor data and associated RCD. For controlled loads, include the contactor, control circuit and manual override. On multiphase circuits, note occupied phases; on single-phase circuits, a phase schedule helps expose later imbalance. Confirm that neutrals belong to the correct RCD zone and protective-conductor terminals remain accessible.

A photograph is useful supporting evidence, not a substitute for structured data. Terminal labels must agree with the diagram and board strip. Record torque or thermal follow-up values only when they come from manufacturer instructions or an execution report. An unverified value does not become safer by appearing in a drawing.

Keep the released PDF with the inspection report, measurements and relevant data sheets in the installation file. Do not overwrite it after an extension: increment the revision, set the new revision date and describe the change. This preserves which drawing represented the physical board at each inspection.

• FPS Economy: official RGIE/AREI books, including Book 1 Version 06
• Book 1 V06, section 3.1.2 for diagram and document data, and Parts 4 and 5 for protection and equipment selection.

Related Articles

• What Is a Single-Line Diagram?
• 30 mA RCD Mandatory per Socket Circuit
• Cable Cross-Section and Breaker: The Right Combination
• PV System in the Diagram

Plan your distribution board visually with the PlanElec Cabinet Editor and place modules on the DIN rail. The advisory self-check does not replace professional review or an official inspection. Try it now →