A wallbox at home: what it gives you and what it asks for

The wallbox does not charge. The charger sits in the car — the onboard charger, which rectifies alternating current and feeds it to the battery. The wallbox supplies that alternating current, watches the connection and tells the car over a thin pilot wire how much current it may draw. That is all it does, which is why the box on the wall is almost never the limiting factor.

The power that arrives is voltage times current times the number of phases. A domestic socket carries one phase at 230 volts and will take about ten amps continuously — a little over two kilowatts. A three-phase supply at 400 volts and 16 amps per phase gives eleven kilowatts, at 32 amps twenty-two. Between a socket and a three-phase wallbox lies roughly a factor of five to ten.

The second difference is sustained load. A domestic socket is built for brief peaks, not for ten hours close to its rating. A wallbox is designed for exactly that: it measures the temperature at its contacts and reduces the current before anything gets warm.

The first question is not how strong the wallbox may be but how strongly the car can charge. The onboard charger is a fixed piece of hardware. Many cars take eleven kilowatts across three phases, some only a single phase, a few up to twenty-two. A twenty-two kilowatt wallbox on a car that charges single-phase charges single-phase — the money for the bigger box is spent and nothing changes.

Single-phase charging has a second catch: phase imbalance. If only one of the three phases draws current, the local network is loaded unevenly. Grid operators therefore cap the permitted continuous single-phase load. The figure that applies is in the grid operator's technical connection conditions, not in the wallbox brochure.

In practice: charge on three phases and a mid-sized battery fills overnight without you thinking about it. Charge on one and you do the arithmetic — capacity divided by charging power gives the hours, plus about a tenth for losses in the charger and the cable. For a commute that is often enough; for a large battery from ten per cent to full it no longer fits into one night.

Between the distribution board and the parking space runs a cable, and its cross-section decides what is possible. Eleven kilowatts need a five-core supply on its own breaker; over longer runs the cross-section has to grow, or too much voltage is lost on the way. In a house with the garage at the far end of the plot, the most expensive item is not the wallbox but the trench.

The second limit is the total capacity of the house connection. Hob, water heater, heat pump and wallbox cannot all run flat out at once. Load management solves it: it measures the current at the house connection and throttles the wallbox as soon as other loads come on. It costs extra and in many cases saves you upgrading the connection itself, which costs several times as much.

If you are getting a quote, supplying these details up front saves a visit:

Every charging point needs a residual current device. What differs from the rest of the house is the kind of fault: a car with a DC link can, in a fault, produce a smooth direct residual current. An ordinary type A device does not detect it — and can even be desensitised by it against the faults it would otherwise catch.

So a wallbox needs either a type B device or a type A together with DC residual current detection that trips in the milliamp range. Many wallboxes have that detection built in; then a type A outside is enough. This is not brochure detail — it is the point at which an installation is signed off or is not.

Add a dedicated breaker per charging point and a check of the protective earth. Anyone who wires a wallbox onto an existing cooker circuit themselves saves money once and loses their insurance cover if anything happens. Sign-off by a registered installer is the record that the installation meets the applicable standard.

A charging point has to be notified to the grid operator, and above a certain power it needs consent. Where that threshold sits and which form applies is set by the local grid operator, which is also the body that receives the notification. Normally the installer handles it, because they have to be on the register to do so.

Processing takes weeks rather than days — an order of magnitude, not a promise. Order the wallbox only when the car is delivered and you will spend the first few weeks on a domestic socket. Order it when you sign the purchase contract, not when the car arrives.

Grant schemes exist at national, regional and municipal level, and sometimes at the grid operator. They change often, and many require the application before installation begins — an application made afterwards is refused however well founded it is. So no figure here, only the order: first check whether a scheme exists, then apply, then build.

In a shared building the wallbox is rarely a technical problem and almost always an organisational one. In several European jurisdictions tenants and flat owners have a right to install a charging point at their own expense. How far that right goes and what deadlines apply varies; what counts is the law where the building stands, and the local tenants' or owners' advice service is the place to ask.

Technically it is worth looking at the common infrastructure. A properly sized riser with load management serving every space is expensive once and cheap for each connection afterwards. Whoever goes first with an individual cable may take up capacity that everyone else later lacks — and the neighbours pay for that.

The third question is billing. A calibrated meter per space separates charging from communal electricity cleanly and makes later arguments unnecessary. Without one, the community pays — and that lasts exactly until the second car arrives.

The financial advantage cannot be given as an amount here, because electricity prices differ by country, supplier and tariff and change constantly. The structure, though, is the same everywhere: at home you pay the unit rate of your domestic tariff and nothing else. On the road you pay the operator's unit rate, depending on the tariff a session or time fee, and at a roaming charger a surcharge on top. Put your own tariff into that and the sum is correct for you.

The second gain is time, and it is underrated. A car that stands still overnight anyway charges while nobody waits beside it. The drive to the charger, the waiting, the hunt for a free bay — all of it goes, on every day of the year.

The third gain concerns the battery. Charging at eleven kilowatts means a low C-rate, little waste heat and a steady current. Charging at home also lets you leave the limit at eighty per cent and only fill up before long trips. That is the gentlest regime available in daily use — and in a few years' time it shows in the remaining capacity when you sell.

The order matters more than it looks. Buy first and ask about charging afterwards, and you have already ruled out every cheap answer. Five questions are enough:

None of these questions needs a specialist, and all five can be answered in an evening. Leaving them open does not change the decision — it only delays it, and by then the car is already outside.