Which connection size for an all-electric new build?

For most large all-electric houses, request the standard three-phase 400 V connection and plan load management from day one. A home battery with a strong inverter then covers the short moments when the heat pump, the charger and the kitchen all run together. Request more kVA only when your long, heavy loads really need it, or when your house will be on the grid in Brussels.

You are building without gas: in Flanders a new house with a permit requested from 2025 no longer gets a gas connection. The heat pump, the induction hob, a charger for one or two cars, maybe a sauna or a pool. Then the Fluvius form asks for "the desired power" and whether you will charge an electric car. Your electrician says "take 3x40 A to be safe". A forum says 25 A is plenty. Nobody tells you what the number actually changes.

Here is the part that stays hidden. The connection size is a ceiling: go over it and the main breaker trips. But in Flanders it barely changes your bill, because you pay grid costs on your measured peak. And asking for more than the street can give can cost far more than the connection itself. One Flemish builder was told about 400 euro extra for a 400 V connection. The offer came to 5,461 euro. The nearby 400 V cable was too light, so the new cable was counted from the cabin, 384 metres away.

A new house in Lokeren shows the other end of the scale. It was built without any grid connection at all, on solar panels, an LFP battery and a generator for dark weeks. Most houses do not need to go that far. But the same logic applies: decide the power with the battery, not after it.

Which connection does a new house get as standard in Belgium?

In Flanders the standard is a three-phase connection: 25 A at 400 V (17.3 kVA) or 40 A at 230 V (15.9 kVA). Which one depends on the grid in your street. Other sizes are possible on request.

Fluvius states that a standard connection gives enough electricity for household use, such as heating, lighting, washing and cooking, and for charging an electric car. Its voltage checker shows whether your street has a 400 V or a 230 V grid. In Wallonia, ORES offers single-phase, 3x230 V and 3x400 V + N, and a simulator that suggests a power for your house. In Brussels, most meters give 9.2 kVA, according to Energuide.

The table comes from ORES and works the same everywhere in Belgium. Keep one detail in mind: the amps apply per phase. On 3x400 V + N with 25 A, each phase gives about 5.75 kW to the loads connected to it. A large single-phase load can trip one phase while the total is still far below 17.3 kVA. Struggling with an older 3x230 V grid in your street? Our article on a 3x230 V connection that is too weak explains the options.

How much power does an all-electric house draw at once?

Far less than the sum of its appliances, most of the time. Energuide puts the typical household peak at 5 to 6 kVA. In Flanders the average monthly peak is 4.24 kW.

The problem is the rare evening when everything overlaps. A large house can hold several heavy loads that each take a real share of the connection.

Together that is 37 kW against a ceiling of 17.3 kVA. In practice these loads rarely peak together for long. The heat pump modulates, the dryer cycles and a smart charger can slow down. The question is not "how much can I switch on", but "what runs together for more than a few minutes". That long overlap sets the connection. The short spikes can be handled in other ways. How a heat pump behaves on a battery is covered in heat pump and home battery. How a charger changes your peak is in home battery and EV charging.

What does a bigger connection cost, once and every year?

In Flanders a bigger connection costs a few hundred euro more once, and nothing extra every year. In Brussels it does cost more every year, and that will grow from 2028.

Two details make the Flemish choice easier to judge. Upgrading later costs more than choosing right now: from 17.3 to 27.7 kVA costs 800.65 euro excl. VAT. At the start the same step adds about 534 euro. And after an upgrade the installation must be inspected again. Lowering the power later without changing the meter costs 266.77 euro excl. VAT.

Brussels works the other way round. In a draft decision of March 2026, Brugel plans a capacity tariff per kVA made available from 1 January 2028, in steps of 1 kVA. Lowering that power is free under the approved tariffs. There, every kVA you do not request becomes a lasting saving.

The yearly cost in Flanders is your monthly peak, whatever size you request. How a battery holds that peak is explained in does a home battery lower your capacity tariff.

When is the grid, not the price, the real limit?

When the power you ask for is not in your street. Then the question is no longer the connection price, but the grid works behind it.

If your construction site is still waiting for power, read what to do when a site connection comes too late. When the grid extension costs more than a battery, the trade-off is set out in grid extension cost versus a battery.

How can a battery let you choose a smaller connection?

By adding its own power when the house asks more than the grid may give, and refilling when the load drops. Victron calls this PowerAssist.

Victron describes it simply: peak power is often needed only for a limited time. The inverter then compensates insufficient grid power with power from the battery. With an energy meter at the grid connection, Victron ESS also counts loads outside the battery output. Think of a heat pump or a charger. That makes the battery a second supply next to the grid, not only a store for solar power.

Three things decide whether it works in your house. First, the inverter power must cover the gap between your limit and your worst overlap, per phase. Second, the battery must hold enough energy for the length of that overlap, also on a dark January evening. Third, the heavy loads must be measured, so the system sees them. A three-phase house needs a three-phase inverter set to do this on every phase. See three-phase home battery for full back-up. How many kWh and kVA a large house needs is in how big should the battery be.

Where does a battery not replace a bigger connection?

Where a heavy load runs for hours. A battery bridges peaks; it does not replace power that you need all evening.

A battery also brings what a bigger connection never does: power during a grid outage. What real back-up needs is in home battery with backup power. How the switchboard of such a house is built is in how a full no-break house is wired.

What if you build without a connection, or keep the grid as a back-up?

Then the connection question turns around: the grid becomes the back-up, or disappears. That is a design choice for the pre-study, not for the connection form.

The new house in Lokeren has no connection at all: no connection costs, no meter and no electricity bill. Solar panels on a flat roof and an LFP battery supply the house, a storage area and a large garden. A generator helps in periods with high use or little sun. The battery capacity was set in the pre-study and can be expanded later. The solar panels were needed anyway to reach the E-level. What does and does not count in that score is in off-grid new build and the E-level.

Between both extremes sits the semi off-grid system. The house runs on its own solar and battery. The grid acts as a generator when the sun and the battery run out. What building without any connection involves is in no grid connection for your new building. For Wallonia, the questions to ask your builder are in building an energy-autonomous house in Wallonia.

What do you put on the connection request?

A list of what runs together, not a list of everything you own. Fluvius asks for the desired power and whether you will charge an electric car.

In Flanders, a new electricity connection must be inspected before its first use. Plan the battery before that inspection, so the switchboard is built once.

How do we size the connection and the battery together?

We start from your appliances and your plans, then choose the connection and the [home battery](https://www.youpower.be/en/products/home-battery) as one system. Our team has three certified battery specialists.

In Kortenberg the house runs on three-phase batteries with full back-up in off-grid mode. In Wetteren a three-phase home is a full no-break: the entire house is powered by the battery.

1. Step 1: We list your heavy loads, how long they run and which ones overlap, before you file the connection request.
2. Step 2: We advise the connection size and voltage, and the inverter power and storage that go with it.
3. Step 3: We install and set the limit, the reserve and the back-up circuits, with an energy meter that sees the whole house.
4. Step 4: You follow everything in the free VRM app, and the battery can be expanded when the house changes.