Low or medium voltage: what changes for your business?

If a transformer in your own cabin feeds your site, you are on medium voltage. If your main board hangs directly on the street cable at 3 x 400 V or 3 x 230 V, you are on low voltage. The difference decides how your grid costs are calculated, who inspects and maintains what, and how fast you can grow. Are you on low voltage and about to outgrow it? A semi-off-grid system turns the street connection into a charger and lets solar and a battery carry the peaks. That often keeps an SME or farm off the medium-voltage route.

Maybe the question came up because of a letter. The grid operator writes about "access power". The electrician says your next machine "needs a cabin". Or you read "high voltage" and think of pylons along the motorway. Many business owners never knew which grid they were on. They find out only when they want to grow.

That is when it gets expensive to guess. The line between low and medium voltage changes your bill, your duties and your timeline at the same time. A cabin is not a bigger fuse. It is an installation you own, inspect every year and plan downtime for. And once you cross the line, the way you pay for the grid changes too.

A farm in Tielt stood at that line. To expand, it would have had to switch to medium voltage, which would have been very expensive. A battery system now gives the site more power, so no reinforcement was needed. The street connection stays, but only as a charger.

What is the difference between low voltage and high voltage?

In Belgium, low voltage means up to 1,000 V alternating current, and high voltage means everything above. That is the split in the AREI (the Belgian electrical safety code). Book 1 covers installations up to 1,000 V, Book 2 installations above (AREI, Royal Decree of 8 September 2019).

In daily use, people add a middle step. The grid that feeds business parks and villages runs at a few thousand to a few tens of thousands of volts. Engineers call it medium voltage. Fluvius and the AREI call it high voltage, and the tariff lists split it into 1-26 kV and 26-36 kV (Vlaamse Nutsregulator tariff list 2026). This article says "medium voltage" for that grid.

The transmission grid sits above it. Elia carries electricity at 380, 220, 150 and 110 kV, and in Flanders also runs the local transmission grid from 70 to 30 kV. Over that grid, power flows from producers to the distribution grid operators and to large industrial users (Flemish government, the high-voltage grid in Belgium).

So "high voltage" in a conversation with Fluvius usually means the medium-voltage distribution grid, not the pylons. The very largest industrial sites connect straight to Elia. For an SME, a farm or a warehouse, the question is simpler. Does the transformer belong to the grid operator in the street, or to you?

How do you know which grid your business is on?

Look for a cabin, then look at the invoice. Four signs tell you in a few minutes.

• A cabin with a transformer on your own site. If it feeds only your company and you pay for its inspection, you are a medium-voltage customer.
• The tariff group on the invoice. Fluvius tariff lists have groups for low voltage, for 1-26 kV, for 26-36 kV and for customers on a distribution cabin.
• "Access power" on the bill. Since 1 January 2023, Fluvius customers outside the low-voltage group pay half of their capacity tariff on a reserved access power (Fluvius).
• The voltage at the main board. 3 x 400 V + N or 3 x 230 V means low voltage. Our article on a 3x230 V connection that is too weak explains why that difference matters too.

One case sits in between: the distribution cabin. Some older sites are connected on the low-voltage side of a grid operator's cabin, with their own tariff. According to the Fluvius tariff sheet, that connection is only kept for existing customers (Fluvius Klantvragen 2026).

When does a business have to move from low voltage to medium voltage?

In Flanders, a connection below 25 kVA is always low voltage, and above 250 kVA always medium voltage with a customer cabin. In between, Fluvius decides. That rule is in the Fluvius tariff sheet (Fluvius Klantvragen 2026).

In Wallonia, ORES treats requests between 56 and 250 kVA as medium power, with a paid detailed study (ORES). ORES speaks of medium-voltage connections from 56 kVA. Those are the ones hit by limited power on the Elia grid (ORES access to power).

What pushes a company over the line is rarely the average use. It is the peak: a new compressor, a cold store, a press, chargers for the vans, a heat pump that replaces the gas boiler. The question is not how much you use. It is how high your peaks go and how long they last. Our article on peak demand in a business shows how to read them. What the cabin itself involves, and what it costs, is in our article on whether you need a medium-voltage cabin or a battery.

What changes on your bill between low voltage and medium voltage?

On low voltage you pay the grid mainly per kW of peak and per kWh. On medium voltage you pay mainly per kVA reserved and per kW of peak, and far less per kWh. The table uses the 2026 tariffs of Fluvius Antwerpen as an example.

Source: Vlaamse Nutsregulator, tariff list Fluvius Antwerpen 2026. Other network areas have other amounts, but the same structure.

Take a company that uses 400 MWh a year. On low voltage, the kWh part of its grid charges comes to about 20,200 euro. On medium voltage it is about 1,650 euro. But medium voltage adds the access power, the cabin and its upkeep, so the saving is never the whole difference. That is why suppliers advise a cabin only for large users. ENGIE, which also installs cabins, wrote in 2021 that a cabin may make sense above 150 MWh a year on low voltage (ENGIE).

Two more rules come with access power. You can raise it every month, but after a choice or an increase you cannot lower it for 12 months. And an excess is charged over 12 months, not one (Fluvius). Old manual meters above 56 kVA and 80 A are being replaced by automatically read (AMR) meters. This customer group gets a monthly invoice (Fluvius). The capacity tariff itself is explained in our article on how to calculate the capacity tariff for businesses.

What changes in duties and safety when you have your own cabin?

On medium voltage the cabin is your installation. You supply and place it; Fluvius supplies the meters and the connection (Fluvius connection guide for high voltage). That brings duties a low-voltage customer never has.

• A yearly inspection. Installations above 1,000 V are checked every year by an approved body. Other installations of a company every five years (FOD Economie).
• Planned downtime. The installation must be able to be switched off for that visit (AREI Book 2).
• Restricted access. The AREI foresees rooms that only instructed (BA4) or skilled (BA5) persons may enter.
• Losses that never stop. A transformer loses energy all the time, whatever you consume. An oversized transformer wastes money every hour (Energie+).
• A new EAN and a supply contract for the new high-voltage connection point (ENGIE).

None of this is a reason not to go. It is a reason to know what you sign up for. Already on medium voltage, and is the transformer itself too small now? Read our article on a cabin transformer that is too small.

What does the grid level change for solar panels, batteries and grid congestion?

Congestion mainly hits requests for extra power on the medium-voltage grid. Households on low voltage are not affected today, ORES writes. Businesses asking for more than 56 kVA in a congested zone are (ORES).

In Flanders, Fluvius offers flexible connections for new connections and expansions in zones where congestion is expected. You get access to the power you ask for, but Fluvius can ask you to limit it for a while (Fluvius). So the step up to medium voltage can come with conditions, and with a date you do not control. Our article on a heavier connection that is refused lists the routes.

A battery has to be reported to Fluvius. Above 25 kVA, a grid study follows (Fluvius). On medium voltage a battery can sit behind your own transformer. On low voltage it sits behind the main board.

Low voltage or medium voltage: which is better for a business?

Neither is better in general. The right grid follows your load profile.

A farm in Tielt shows the first case. The battery system gives the site more power, solar panels supply the energy, and the street only steps in when the battery runs low. The farm will take only about 5% of its yearly consumption from the grid.

A site in Beveren-Melsele shows the other end. It uses about 350,000 kWh a year. We installed 200 solar panels and a 154 kWh battery to use as much of that solar power as possible on the spot. The design leaves the remaining peak current to a high-voltage cabin. For that load, the cabin is the right tool, and the battery works next to it.

Can your business stay on low voltage while it grows?

Often, yes, as long as the extra need comes in peaks and not as a constant load. The connection delivers the base load; stored energy delivers the rest.

Our semi-off-grid system is built for SMEs and farms with a standard 3 x 400 V + N connection. The grid acts as a generator: it steps in at night, on dark days or when the battery is empty. And the site keeps working during a grid outage. For larger grid-tied sites, a business battery system behind the existing connection covers the peaks and grows in modules up to 1 MW.

It stops working when the peak lasts all day. A battery needs quiet hours to recharge. If there are none, you are sizing a battery to replace a cable, and the cabin wins. Moving into a new building instead? Then first read our checklist for checking the grid connection of a business building.

What happens when you ask us to look at your connection?

We start from your invoice and your peaks, before anything is designed.

1. Step 1: Analysis. You send us an invoice and your quarter-hour peaks, or we monitor your consumption for a short period first.
2. Step 2: Sizing and technical design. We tell you whether your growth fits on low voltage with a battery or a semi-off-grid system, or whether a cabin is the better route.
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.