How do you check a business building's grid connection?

Get five facts in writing before you sign. You need the connection power in kVA and the voltage, and whether the site is on low or medium voltage. Add who owns the cabin, whether the connection is shared, the monthly peaks of the current user and the congestion zone. Then compare that with what your machines, chargers and heat pump will really draw. Does the connection fall short? Ask for an upgrade, or bridge the gap on site with a semi-off-grid system. It turns the existing connection into a charger and often saves the medium-voltage step.

You have found the building. The location is right, the price is right, and the listing says "three-phase power available". You plan to move in three months. Then the electrician looks at the main fuse, or the new compressor trips it on the first day. Suddenly you are asking the grid operator for more power, and the answer is a study, a quote and a date you do not control.

That is the trap. The move date is fixed, the connection date is not. The notary and the agent check the deed, the permit and the energy label of the building. Nobody checks whether the connection can carry your business. And the obvious fix, a heavier connection, can turn into a medium-voltage cabin with its own inspections.

A plant nursery in Jabbeke had 3 x 400 V with 32 A. A new irrigation pump needed more, and the proposal was medium voltage at a high price. The nursery kept its street connection instead. It now only charges a battery system that delivers a heavier 63 A to the pumps.

What does the connection power of a business building mean?

The connection power is the maximum the grid can deliver to the building at the same moment, expressed in kVA. It follows from the voltage, the number of phases and the rating of the main fuse or breaker. "Three-phase" alone says nothing: a small and a large connection can both be three-phase.

You can work it out yourself. For a three-phase connection, kVA = 1.73 x voltage x amps / 1,000. Fluvius uses the same standard sizes in its 2026 tariff sheet. The table shows the most common ones.

Calculated values, matching the standard sizes in the Fluvius tariff sheet Klantvragen 2026.

Two more things decide what you can do with that power. The voltage: on an older 3 x 230 V network the same fuse gives less power. And many heat pumps, chargers and inverters expect 400 V. Our article on a 3x230 V connection that is too weak explains the difference. The grid level: above a certain size the building is not on low voltage at all, but on medium voltage with its own cabin.

How do you find out which connection a business building has?

Ask for documents, not for a description. Four sources give you the real figure, and the seller or landlord can usually provide all of them within a week.

• The main breaker or fuse. An electrician reads the rating in amps and the voltage in five minutes. Ask for it during the visit.
• The connection contract or the grid operator's letter. For larger sites this states the contracted connection power in kVA.
• The meter. A digital meter shows the highest quarter-hour peak of the current month under code 1.6.0 (Fluvius). A medium-voltage site has its own metering in the cabin.
• The grid operator. In Flanders that is Fluvius. In Wallonia it is ORES or RESA, in Brussels Sibelga. They can tell the owner what is connected at the address.

Then check whether the connection is shared. In a business park or a building split into units, several companies sometimes hang on one connection or one cabin. Fluvius only allows that exceptionally, with its explicit consent and a contract between the users. That contract sets who pays the yearly inspection, the repairs and any reinforcement. Ask for it: it tells you how much of the power is really yours (Fluvius annex "cabin with several grid users").

Is the business building on low voltage or medium voltage, and who owns the cabin?

Up to 25 kVA a Fluvius connection is always low voltage. Above 250 kVA it is always high voltage, with a customer cabin. In between, Fluvius decides. That rule comes from the Fluvius tariff sheet, and it matters a lot when you buy or rent. What the grid level changes for your costs and duties is explained in low voltage or medium voltage for a business.

On medium voltage (Fluvius calls it high voltage) the cabin is yours as the customer. You supply and place it, Fluvius supplies the meters and the connection, according to its connection guide for high voltage. That brings duties you take over with the building:

• A yearly inspection of the high-voltage installation by an approved body. Low-voltage installations in a company are inspected every five years (FOD Economie).
• The reports and the file: ask for the latest inspection report, the single-line diagram and a list of any remarks that still need fixing.
• Maintenance and replacement: an old transformer or old switchgear is your cost after the purchase.

Renting? Then agree in writing who carries these costs. Some older sites are on a distribution cabin of the grid operator, which is a different case again. According to the Fluvius tariff sheet, only existing customers keep that tariff. It can be lost when an upgrade needs a new cable. Our article on whether you need a medium-voltage cabin or a battery goes deeper into the cabin itself.

Where do you see if there is grid congestion at the address?

In Flanders, Fluvius publishes a congestion map per power supply area. In orange zones only flexible connections are possible. In yellow zones, customers who ask for 1 MVA or more get a flexible connection. In green zones classic connections are still possible.

Fluvius calls the map indicative and not binding. It is about extra power on the medium-voltage grid, so it matters most for sites that plan to grow. On 15 September 2026, 335 requests for a classic connection and 327 requests with flexibility were still waiting for a quote (Fluvius figures and maps).

In Wallonia, ORES writes that several zones already show a high risk of congestion. Requests for medium and high power take longer because the detailed studies are made with Elia. For needs above 250 kVA in a constrained zone, ORES can offer a connection with flexible power (ORES). Its advice: ask for the detailed study as soon as your project is defined.

How much power will your business need in the new building?

Start from what you measure today, not from the nameplates. Adding up the power of every machine gives a number far above what you really draw, because not everything runs at the same time. The quarter-hour peaks of your current site tell you what you need.

Log in to Mijn Fluvius for your current site and download your monthly peaks and quarter-hour values. Then add what will be new: an extra compressor, a press, a cold room, chargers for vans or forklifts, a heat pump. Look at three things: how high the peaks are, how long they last and how often they come back. Our article on peak demand in a business shows how to read them.

No data yet, because the business is new or the building is still under construction? Then measure first. A garden contractor in Zele was building a house and a warehouse, and the future consumption was not known. We monitored the average and peak consumption for one month and sized the installation on that.

What should be on your checklist before you sign?

Put these eight questions to the seller or landlord, and get the answers in writing before the deed or the lease.

What does a heavier connection cost, and how long does it take?

The fixed part is known, the timing is not. Fluvius publishes its prices for 2026, but it gives no standard term for a business upgrade: the date comes with the quote, after the study.

Source: Fluvius tariff sheet Klantvragen 2026. Work on your own installation, the main board and the cable to it, comes on top.

Take a workshop that moves from 22.2 kVA to 55.4 kVA at 400 V. Fluvius lists 1,429.70 euro excl. VAT for that adaptation, as long as the cable, the meter and the local grid are strong enough. The extra power comes on top: about 33 kVA at 27.59 euro, roughly 915 euro. Add the study and your own work, and it stays manageable. The real cost is the wait, and the jump when the need crosses 250 kVA: then it becomes a customer cabin with its own inspections. If the grid operator refuses or postpones the upgrade, our article on a heavier connection that is refused lists the routes.

What can you do if the connection of the building is too small?

You have four routes, and the right one depends on the size and the length of your gap. A short, predictable shortfall is a different problem from hours of high load every day.

A farm in Tielt is a good example of the semi-off-grid route. To grow, it would have had to switch to medium voltage. The battery system now gives the site more power, so a heavier connection was not needed, and the street only charges the battery. In Wielsbeke a flax processor avoided a large medium-voltage cabin for one heavy machine. A generator starts the machine and charges the batteries at the same time.

For larger sites, a business battery system behind the existing connection covers the peaks and grows in modules up to 1 MW. And where the street has no grid at all, a building can run without a connection. A rental company in Zele did exactly that for its warehouse, offices and electric lifting equipment. Our article on a new building without a grid connection explains how.

Adding one big machine or pump to a building you already use? Then our article on more power without a heavier connection is the better read.

What happens when you ask us to look at a building?

We start from your figures and the building's figures, before anything is designed.

1. Step 1: Analysis. You send us the connection data of the building and the peaks of your current site. If data is missing, we can monitor your consumption for a short period first.
2. Step 2: Sizing and technical design. We compare your need with the connection and tell you whether the gap needs an upgrade, a battery or a semi-off-grid system.
3. Step 3: Installation and commissioning.
4. Step 4: Monitoring and support. You follow consumption and the battery in the app and the VRM portal, as explained on our software page.