The electrical side of an air conditioner: circuit, breaker and contracted power

Updated September 3, 2026 · Claude AC · 2 sources cited

Contents (8)

What the machine actually draws
A dedicated circuit, not a spare socket
Breaker, RCD and cable: the manual decides
The contracted power trap
What the electrician finds in an older European building
Solar panels and vehicle chargers on the same board
Six checks before installation day
Frequently asked questions

Almost every air conditioning project in Europe is discussed as a refrigeration project: which capacity, which brand, where the outdoor unit goes. Then the fitters open the consumer unit and the conversation changes — no free route to the board, no spare space in it, a flat on a 3 kW supply contract, or a cable someone ran last winter that is two sizes too small. The electrical work is where European air conditioning quotes most often go wrong, because it depends on a building nobody surveyed before quoting.

What the machine actually draws

A split system is a modest electrical load compared with an oven or a shower, but it is a load that runs for hours. Input power is roughly the cooling capacity divided by the efficiency at that moment, so a well-rated unit consumes a third or less of the kilowatts it delivers. The figures below are indicative orders of magnitude for modern inverter splits at 230 V single phase, not a specification: the number that governs the circuit is the maximum operating current on the nameplate, which is well above the average.

Indoor capacity	Typical input at rated cooling	Typical average current	What the circuit is sized on
2.5 kW — one bedroom	around 0.7–0.9 kW	3–4 A	Nameplate maximum, commonly 8–12 A
3.5 kW — living room	around 1.0–1.2 kW	4–5 A	Nameplate maximum, commonly 10–16 A
5 kW — large room	around 1.4–1.8 kW	6–8 A	Nameplate maximum, commonly 16 A
7 kW multi-split, several indoor units	around 2.0–2.5 kW	9–11 A	Nameplate maximum, often 16–20 A

Two details change the picture. The sizing case is frequently heating, not cooling: on many reversible models the declared maximum current in heating exceeds the cooling figure. And inverter drives start softly, without the inrush of an old fixed-speed compressor, so the problem is rarely the moment of starting and almost always the sustained load added to everything else in the home.

A dedicated circuit, not a spare socket

Small wall splits sometimes arrive with a moulded plug and a manual that authorises a standard socket outlet. Everything larger, and every multi-split, is a fixed connection fed by its own circuit from the board, with a means of isolation the technician can lock off near the outdoor unit. National wiring rules differ in the detail — NF C 15-100 in France, BS 7671 in the United Kingdom, the DIN VDE 0100 series in Germany, CEI 64-8 in Italy, the REBT in Spain — but they are all national implementations of the same CENELEC HD 60364 framework, and they converge on the same three requirements: a circuit sized for the load, protection appropriate to the equipment, and accessible isolation for maintenance.

Sharing the machine with a lighting or general socket circuit is the shortcut to avoid: a nuisance trip then takes the air conditioning down with the freezer, and a fault in the machine takes down half the flat during a heatwave. The isolator matters just as much — a technician who has to walk to a communal riser to make the unit safe will charge for it, every visit.

Breaker, RCD and cable: the manual decides

Every manufacturer publishes an installation table giving the maximum protective device rating and the minimum conductor cross-section for each model. That table, read against the national rules and the actual cable run, is what determines the installation — not a rule of thumb from a forum. As orders of magnitude, small units are typically found on a 10 A circuit in 1.5 mm², the common 3.5 to 5 kW range on 16 A in 2.5 mm², and larger multi-splits on 20 A, with the cross-section increased when the run is long.

Residual current protection is where a general electrician can get an air conditioner wrong. A 30 mA device is the European norm, but the type is not a detail: an inverter drive is a frequency converter, and converters can inject smooth DC residual current that a basic type AC device does not see. Type A is the realistic minimum, several manufacturers specify type F or type B, and the usual engineering threshold is whether the drive limits smooth DC leakage to 6 mA or less. The answer is printed in the manual for your exact model; anything else is a guess with a safety function attached.

Between the two units runs an interconnecting cable, usually four or five cores, sized by the manufacturer and rated for outdoor conditions wherever it is exposed. Joints in it are a classic source of the communication faults that later surface as an unexplained error code.

The contracted power trap

This is the European specificity that surprises buyers most, because it does not exist in the same form in North America. In much of Europe the household does not simply take what it needs: it subscribes to a level of power, and exceeding it either trips the supply or costs money.

Country	How the limit is expressed	What adding air conditioning usually means
Italy	Contracted power, historically 3 kW in flats	Frequent meter trips when the oven, the hob and the split run together; many households move to 4.5 or 6 kW
Spain	Potencia contratada, common steps around 3.45, 4.6 and 5.75 kW	Either careful sequencing of appliances or a step up, billed every day of the year
France	Subscribed power in kVA, typically 6, 9 or 12	A single split rarely forces a change; a multi-split with electric cooking and a vehicle charger often does
Netherlands	Physical connection size, commonly 1×25 A or 1×35 A	The connection capacity sets a fixed network charge; enlarging it is grid work, not a phone call
Nordic countries	Main fuse rating, which the network tariff follows	The main fuse, not the machine, is usually the binding constraint in older flats

The consequence is a running cost people forget to count: raising the contracted power raises the standing charge permanently, hot summer or not — a fixed line to add to the arithmetic in our guide to what air conditioning costs to run in Europe. It is also an argument against oversizing, since an oversized machine can be the item that pushes a household into the next tariff band. The method is in our guide to sizing an air conditioner in kW.

What the electrician finds in an older European building

Europe’s housing stock is old, and the electrical reality behind the plaster decides a large share of the installation price:

No protective earth on circuits in pre-1970s installations, which means a new circuit run all the way back to the board rather than a local tap.
A full consumer unit with no free way for another device — a small extension enclosure is cheap, discovering the need on installation day is not.
A long route from the board to the outdoor unit, through a stairwell or a shaft that belongs to the building rather than to you, which is a co-ownership question as much as a technical one.
An older main fuse or supply cable that limits the whole flat regardless of what the new circuit can carry.
Aluminium conductors or shared neutrals from a 1960s–70s refurbishment, where extending anything means replacing rather than adding.

All five belong in the quote as itemised lines before the work starts, which is exactly why an unseen quote issued over the telephone is worth so little — the comparison logic is set out in our guide to installation costs across Europe.

Solar panels and vehicle chargers on the same board

Cooling demand peaks when a roof produces most, which is the self-consumption case examined in our guide to solar panels and air conditioning. The caution is that several inverter loads on one domestic supply need a deliberate look at total demand and at residual current protection — and that a vehicle charger with dynamic load management, set to yield to the rest of the house, is far cheaper than upsizing the supply.

Six checks before installation day

Read the maximum operating current and the recommended protection from the installation manual of the exact model quoted, in heating as well as cooling.
Ask who provides the circuit: the air conditioning company, your own electrician, or nobody — the third answer is the one that ruins a fixed price.
Photograph the consumer unit and send the photo with your enquiry. Free spaces, device types and the main protective device are all visible on it.
Check your contracted power or main fuse against the load you are adding, before signing.
Confirm the RCD type required by the manufacturer, in writing, and that the installed device matches it.
Require an isolation point at the outdoor unit and keep the electrical certificate with the machine’s paperwork.

Frequently asked questions

Can I just plug an air conditioner into a normal socket?

Only if the manufacturer supplies a plug and the manual authorises it, which is common for portable units and some small wall splits, and never the case for multi-splits. Even where permitted, the socket should not be shared with other heavy loads, and an extension lead is the wrong answer in every case: a sustained load through a coiled flex is a fire risk, not a compromise.

What size breaker and cable does a 3.5 kW split need?

Typically a 16 A circuit in 2.5 mm² for a domestic run in Europe, but that is an order of magnitude, not an instruction. The manufacturer’s table gives the maximum device rating and minimum cross-section for your model; the national wiring rules then adjust it for the length of the run, the installation method and grouping with other cables.

Do I need a type B RCD for an inverter air conditioner?

Sometimes, and the manual for the specific model is the authority. Inverter drives can produce smooth DC residual current that a type AC device will not detect; type A is the practical minimum, and manufacturers specify type F or type B where their drive can exceed the usual 6 mA smooth DC threshold. Fitting a lower type than specified defeats the protection you paid for.

Will air conditioning trip my supply contract?

In flats with small contracted power it certainly can, which is a widespread situation in Italy and Spain. Add the machine’s maximum current to the loads you genuinely run at the same time on a hot evening — cooking, water heating, a washing machine — and compare with your subscription. Raising it is straightforward but the higher standing charge is permanent.

Can I run the electrical circuit myself and let the fitters connect it?

Some installers accept it, many refuse because they cannot certify what they did not install, and in several countries the work is regulated whoever does it. It also complicates a later warranty claim, since a manufacturer looks at the supply arrangements first. The refrigerant side is never a do-it-yourself matter: it is legally restricted to certified personnel, as our guide to installing air conditioning yourself explains.