When do you need a medium voltage cabin or a battery?

In Flanders a medium voltage cabin (Flemish buyers usually say "high-voltage cabin", hoogspanningscabine) is mandatory as soon as you ask for more than 250 kVA of connection power: Fluvius then always connects you to the high-voltage grid. Between 25 and 250 kVA the grid operator decides. A cabin means your own customer cabin, inspections, yearly inspection visits and a lead time you do not control. If you structurally need a lot of power, that is the right route. If the extra peaks only occur for a few quarter-hours a day, a commercial battery on your existing low-voltage connection keeps you under the limit. That route is often faster. The answer is in your measured quarter-hour values.

The trigger is usually a letter or a study: the new laser cutter or the charge points push the request past 250 kVA, and suddenly the conversation is about a cabin, a transformer and a year of planning. What that letter does not tell you is how many hours a day you really need that extra power.

When do you need a medium voltage cabin?

The requested connection power decides the grid. The 2026 customer requests tariff sheet of Fluvius sets out the rule for Flanders:

Technically it is medium voltage: the Fluvius tariff lists distinguish the 1-26 kV grid and the 26-36 kV grid. Fluvius itself speaks of a customer cabin on the high-voltage distribution grid.

An in-between form, a connection on a distribution cabin of the grid operator, is no longer an option for new customers in Flanders. According to the same tariff sheet, it only applies to existing customers who already had that tariff.

In Wallonia, ORES decides after its study. ORES flags access-to-power problems for requests above 56 kVA, and can offer a flexible-power connection above 250 kVA in zones where power is not always available (ORES).

If you end up just above a threshold, the question is: does my connection power really have to go up, or only my peak power for a short time? For the second there is another answer: a business battery that supplies the peak from stored energy.

What does a medium voltage cabin involve?

The Fluvius connection guide sets out the split clearly. You supply and install the customer cabin; Fluvius takes care of the meters and the connection (Fluvius connection guide). In practice, in Flanders:

• Design according to Synergrid C2/112 and the additional Fluvius rules, plus the study document Fluvius draws up for your connection.
• Remote control. For requests from 1 January 2022, remote control on motorised loop cells is mandatory.
• Single-line diagram and site plan must be delivered at the latest 16 weeks before the connection date.
• Meter cabinet. For requests from 1 January 2025 Fluvius no longer supplies it; you provide it yourself.
• Digging on private land, with three PVC ducts of at least 250 mm diameter.
• Access. Fluvius must be able to reach the meter safely 7 days a week, 24 hours a day.
• Asbestos inventory when you place the cabin in an existing building or replace an old cabin.
• Double inspection by an approved inspection body: compliance with the AREI (the Belgian electrical installations code) and with C2/112.

In Wallonia the split is similar. According to the ORES 2026 connection tariffs, you do the earthworks on private land and lay the ducts, install and equip the cabin (its location and plans need ORES approval) and have it inspected by an approved body before commissioning. The medium voltage meter is installed in the cabin and remains ORES property.

The lead time is on the grid operator's quote. Add the time for design, delivery of the switchgear, construction and inspection, and possibly an environmental permit. In a zone with expected grid congestion you may also be offered a flexible connection instead of a classic one. Offered a flexible connection or a refusal? Then read our article on a heavier connection that is refused or delayed to see your options.

What obligations do you have after commissioning?

A cabin is not a one-off investment but an installation you operate. AREI Book 2 (high-voltage installations) requires, among other things:

• Yearly inspection visits by an approved body, after the conformity inspection. The installation must be able to be switched off during that visit, so plan a yearly shutdown.
• Restricted access. The AREI provides for electrical service rooms that only informed (BA4) or skilled (BA5) persons may enter.

On top of that, the Federal Public Service Employment expects the employer to carry out a risk analysis per electrical installation, keep a file with diagrams, plans and inspection reports, and train staff. For comparison: low-voltage installations are inspected every five years. These rules are federal, so they apply in every region.

What does a medium voltage cabin cost, and which part of the price is fixed?

There is no fixed price for the cabin itself (housing, switch cells, transformer, low-voltage board); it depends on power, design, location and earthworks. What is fixed is the grid operator's part. From the Fluvius 2026 tariff sheet for customers on the 1-26 kV grid in Flanders (excluding VAT):

Not included according to Fluvius: the inspection of the customer cabin, the commissioning of your own installation and the repair of special paving on private land.

In Wallonia ORES publishes its own connection tariffs. The detailed study costs 1,805.98 euro excluding VAT between 250 and 1,000 kVA in 2026 (1,223.41 euro between 56 and 250 kVA), and the medium voltage connection fee is charged per kVA from the first kVA, including grid extension up to 400 metres.

The periodic network tariffs change too. Take the 2026 tariff list of Fluvius Antwerpen. A customer on the 1-26 kV grid pays about 33.66 euro per kVA per year for access power there, plus about 54.30 euro per kW per year for the monthly peak. Exceeding the access power has a separate rate (tariff list). The kWh rate for public service obligations is below 0.004 euro per kWh there, against about 0.0255 euro per kWh on the low-voltage grid. Because of those lower network tariffs, suppliers recommend a cabin with a large annual consumption. ENGIE mentions an annual consumption above 150 MWh on low voltage as the point to consider it.

Does a metal company with 400 kVA need a cabin or a battery?

Illustrative figures, not a customer case.

A metalworking company has a low-voltage connection of 160 kVA. A new laser cutter and charge points for the company cars bring the request to 400 kVA, so high voltage.

Option A: medium voltage cabin. The Fluvius part for a new 400 kVA connection in Flanders, indicative according to the tariff sheet:

On top come the cabin itself, the inspections, the earthworks, the yearly inspection visits and staff with BA4/BA5 authorisation. Your own quote from the grid operator may differ.

Option B: battery on the existing connection. The quarter-hour values of the past year show:

• Highest quarter-hour peak today: 140 kW. Consumption outside the peaks: around 100 kW.
• With the new loads: peaks up to 260 kW, for six quarter-hours (1.5 hours) a day.
• Safe limit on the existing connection: 150 kW.

Is there no 3.3 hours of room to recharge after the peak, or does the peak last all day? Then option B does not work and the cabin is the right choice. If it fits, the company stays on low voltage. The battery does have to be notified to the grid operator: in Flanders, with an inverter above 25 kVA, a grid study follows; in Wallonia ORES asks for a more thorough study above 10 kVA. Plan that in.

How do you choose between a medium voltage cabin and a battery?

Two questions help you choose. How many hours a day are you above the limit? And what happens to your production if the grid drops out? A cabin solves the first, not the second. A battery system with off-grid capability takes over the supply during a power cut. That is what separates a real system from a storage box.

The control sits in the system controller. In a Victron installation, the GX controller with the ESS peak shaving function watches the current at the energy meter (Victron). The battery steps in as soon as the set limit is at risk.

Can a battery fully replace a cabin?

Sometimes, together with a generator. The flax processing company in Wielsbeke would need a large medium voltage cabin to work on the public grid. The company starts its heavy machine with a generator that keeps running during the work. That generator also charges a 30.8 kWh battery with 3 x 8 kVA of charging power, which supplies the electricity for the rest of the day.

If you grow to a few hundred kVA, a combination can be more interesting. A battery makes the expansion possible now, while you plan the cabin for later. Security of supply is an engineering question, not a product purchase. Already have your own cabin, but the transformer has become too small? Read whether you need a new transformer or a battery behind it.