Why a normal socket is not enough for charging

How is this different from a vacuum cleaner

An ordinary socket handles 16 A, but in short bursts. A vacuum runs for twenty minutes, a kettle for four. Charging a car takes ten to sixteen hours and draws close to the socket's maximum the whole time.

Household wiring is not designed for that. It is not that it "cannot be done" — it is what it does to the materials.

Where it fails

• The contacts inside the socket. They loosen with age. Higher contact resistance means heat, and heat means more loosening. It is a loop that ends in a burnt socket.
• Extension leads and cable reels. A coiled cable cannot shed heat. A reel rated 3,500 W unwound will overheat wound up.
• Old aluminium wiring. Common in Prague apartment buildings. Aluminium tolerates thermal cycling worse than copper.
• A shared circuit. The garage socket is often on the same breaker as the lights and the door. The car takes the whole circuit.

When a socket is fine

Emergency charging from a so-called granny charger has its place — at a cottage, at a friend's, once in a while. Three conditions:

• the socket is in good condition and ideally on its own circuit,
• you charge at reduced current, typically 8 to 10 A instead of 16,
• no extension lead, or only one fully unwound and properly rated.

If the socket feels warm after the first session, do not start another.

Portable wallbox: a reasonable compromise?

Between a granny cable and a fixed charger sits the portable wallbox — a cable with a control unit that plugs into an ordinary socket or a 400 V industrial socket.

What it can do: set the charging current (typically 6 to 16 A), so you can dial the draw down to suit the socket. Better units monitor plug temperature and carry their own DC fault protection. With a 400 V adapter they charge three-phase and faster.

When it is enough: at a cottage, at your parents', as a backup in the boot, or if you drive a few hundred kilometres a month and have a sound socket on its own circuit.

When it is not: as an everyday solution at home — for one reason the adverts skip. A portable wallbox does not create a dedicated protected circuit. You are still on a socket that is part of the house wiring with everything else on it. Clever electronics in a cable will not fix a fifteen-year-old socket or aluminium wiring.

Put it this way: a portable wallbox is good supplementary kit, not a replacement for an installation. Most people end up with both.

What a wallbox does differently

It is not a prettier box doing the same job. A wallbox has its own protected circuit run back to the consumer unit, a residual current device that also detects DC fault current (which an ordinary household RCD cannot see), it negotiates with the car how much current it may draw, and it monitors temperature and the state of the wiring.

That negotiation matters: the car itself backs off when the installation cannot cope. A socket can do none of this — it delivers whatever the car asks until something gives.

In short

A socket is a stopgap for a few dozen kilometres. A wallbox is equipment you charge from every day without thinking about it. The difference is not speed — it is that one is designed for sustained load and the other is not.

If you are unsure about the socket you have been using, we will look at it during the site visit.