12-, 24- or 36-module distribution board: how many modules for a home or a shop?

To size a distribution board, count the devices you will fit in it, then keep 20% of its spaces free. A compact phase + neutral breaker usually takes 1 module and a two-pole RCD (residual current device) takes 2. A house with two RCDs and 8 circuits needs 12 modules, or 15 with spare: choose a 24-module board. Our Winline boards come in 12, 24 and 36 modules, surface- or flush-mounted, and in an IP65 waterproof version.

What is a module in a distribution board?

A module is the unit of width for devices clipped onto the DIN rail inside a board. One module is 17.5 to 18 mm wide.

So the module count of a board tells you how much rail space it has, not how many circuits it can feed. Here is the usual width of common devices. It varies by model, so always check the device’s instructions.

• Single-pole breaker: 1 module.
• Phase + neutral breaker: 1 or 2 modules, depending on the model.
• Two-pole RCD: 2 modules.
• Four-pole RCD (three-phase): 4 modules.
• Contactor, timer, impulse relay: 1 or 2 modules.
• Modular surge protector: 1 to 4 modules.

A 24-module board is often laid out as two rows of 12, and a 36-module board as three rows. In British usage, a board’s size is often given in “ways”: one way is one single-module slot.

How do you count modules? The method and two examples

The method has three steps.

1. List every device: RCDs, breakers, contactors, surge protector, and a changeover switch if you run a generator.
2. Add up their modules using the list above or the device instructions.
3. Divide the total by 0.8 (or multiply it by 1.25) so that 20% of the board’s spaces stay free, then pick the board size that matches or is just above that figure.

Choosing the devices and their ratings is your electrician’s job. The examples below only count the space.

Example 1: a house with 8 circuits

You need 15 modules: a 12-module board is too small, so choose 24 modules. NF C 15-100 requires at least two 30 mA RCDs in a home, so a single fault does not cut power to the whole house. A 24-module board also leaves room for an air conditioner, a pump or a generator changeover switch. Replacing a board that turns out too small costs far more later.

Example 2: a shop or small business

You need more than 16 modules: a 12-module board is too small, and 24 is the right choice. In a three-phase workshop, a four-pole device usually takes 3 or 4 modules. The total climbs fast, and a 36-module board often becomes necessary.

Why keep spare space in a board?

An installation almost always grows. A new air conditioner, a pump, a circuit for a generator: each one needs at least one free module. With no space left, you have to change the whole board.

The French wiring standard NF C 15-100 requires at least 20% spare space in a home’s distribution board. It is not law in the DRC, but many electricians and engineering firms use it as a reference. Twenty percent is a sound rule of thumb.

Spare space also makes wiring easier: a board packed full is hard to inspect and repair.

Surface, flush or waterproof: which board should you choose?

The mounting depends on the wall and the location, not on the number of circuits.

• Surface-mounted: the board is fixed to the wall surface. It is the simplest option for a finished wall, a renovation or a plant room. Cables come in from the top, the bottom or through trunking.
• Flush-mounted: the board sits in a recess in the wall and only the door protrudes. It suits new builds where conduits run inside the masonry. Plan the recess before plastering and check the wall depth.
• IP65 waterproof: for outdoors, a garage, a pump house, a building site or a dusty room. The first digit (6) means fully dust-tight, the second (5) means protected against water jets. Our guide to IP ratings explains this choice in detail.

Here are the Winline boards in our range, with the values from our datasheets. “n/s” means the datasheet does not state the value.

For a small outdoor board (pump, gate, garden lighting), the E series also comes in 5 and 8 modules (WN-E1005, WN-E1008). The full range is on our distribution boxes page.

Which accessories go with a board?

• Flush connection boxes and their covers: the WN-G8005 (160 × 130 × 70 mm), WN-G8007 (294 × 152 × 75 mm) and WN-G8008 (400 × 160 × 75 mm) boxes take the white covers WN-G1005 (160 × 130 mm), WN-G1007 (294 × 152 mm) and WN-G1008 (400 × 160 mm). They group wiring connections inside the wall, close to the board.
• Junction boxes to split circuits in each room: see our junction boxes.
• Cable glands to keep an IP65 board sealed where cables enter: see our cable glands.
• Conduits to bring cables to the board: see our rigid tubes and conduits.
• Fisher circuit breaker box (WN-BT1-2, 52 × 130 × 60 mm, or WN-BT3-4, 87 × 130 × 60 mm): a small surface-mounted box that houses one or a few breakers next to an appliance far from the main board (pump, water heater).

Where can you find these boards in Kinshasa?

We are an authorized Winline dealer. You can see the boards at our showroom in Gombe, No. 26, Avenue des Huileries, opposite the INRB, Monday to Friday 8 am to 5 pm and Saturday 11 am to 4 pm. We also deliver to other provinces of the DRC. For fitting, see our installation services.

Ask for a quote on WhatsApp: message +243 903 005 060 with the number of modules, the mounting you want (surface, flush or waterproof) and the quantity. Prices on request.

Frequently asked questions

Is a 12-module board enough for a house?

Rarely. Two RCDs (4 modules) and 8 breakers (8 modules) already make 12 modules with no spare. A 12-module board suits a studio or an annex with 3 to 5 circuits; for a house, choose 24 modules.

How many modules does an RCD or an RCBO take?

A two-pole RCD usually takes 2 modules and a four-pole model 4 modules. An RCBO (combined breaker and RCD) usually takes 2 modules, or 1 for some compact models. Check the instructions, as widths vary between manufacturers.

Flush or surface-mounted: which one should I choose?

Flush for a new build where conduits run inside the wall. Surface for a finished wall, a renovation or a plant room. The number of modules does not change this choice.

What is the difference between E1 and E2 models (WN-E1012/E2012, WN-E1024/E2024)?

All four are IP65 waterproof boards made of ABS, with 12 or 24 modules. The E2 models (WN-E2012, WN-E2024) are the E series’ “New Design” versions. Our datasheets show no other difference: come and compare them at our showroom.

Can a distribution board be installed outdoors?

Yes, with a waterproof board such as the E series (IP65), sheltered from direct rain and sun where possible. Keep cable entries sealed with cable glands.

Sources: Winline product datasheets (mounting, modules, IP rating, material, dimensions), usual width of DIN-rail modular devices, NF C 15-100 (20% spare space, at least two 30 mA RCDs per home; French reference, not law in the DRC), IP codes from IEC 60529.