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

The main RCD (300 mA, Type S = selective) is time-delayed and only trips when the group RCD (30 mA) has failed to respond. This means that in case of a fault, only the affected group RCD trips — not the entire installation.

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: 24 MCBs + 4 RCDs + SPD + main switch = approx. 40 TE occupied out of 72 TE → 44% 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.

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

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