Short answer
For an 11 kW EV charger over a short distance 5 x 2.5 mm² is often enough. If the distance is more than about twenty metres, it goes towards 5 x 4 or 5 x 6 mm² to keep the voltage drop within the standard. Outside and in the ground you need a cable made for that, with the right cover and a warning tape above it.
Who this article is for For anyone who wants to understand where the price of an EV charger installation comes from. The calculation and the installation belong with the electrician.
Why length matters
Some voltage is lost in every cable. With a lamp you do not notice. With an EV charger drawing 16 amps per phase for hours, you do. If the voltage drops too far at the end, the charger starts throttling back or giving error messages, and the cable gets unnecessarily warm.
That is why the standard sets a limit on voltage drop. Making the cable thicker is the solution.
| Distance from meter cupboard to charger | Rule of thumb at 11 kW |
|---|---|
| up to 15 metres | 5 x 2.5 mm² |
| 15 to 30 metres | 5 x 4 mm² |
| 30 to 50 metres | 5 x 6 to 10 mm² |
| more than 50 metres | calculate it, sometimes a separate distribution board |
This is a rule of thumb, not a calculation. The real cross-section follows from length, power, installation method and ambient temperature.
Indoors, outdoors and in the ground
Indoors along the wall or through the crawl space, ordinary installation cable can be used, provided it is neatly fixed and protected where people can get at it.
The order in the garden. The duct is the step people skip and later miss.
Outside on the wall the cable should be UV-resistant or run in conduit. Sun breaks down PVC after a few years.
In the ground you need a buried cable, not an ordinary cable in a conduit from the DIY store. Rules of thumb:
- at least 60 cm deep under a garden, deeper under a driveway where cars drive
- a bed of sand below and above the cable
- a yellow warning tape about 30 cm above it
- a duct you can pull cable through later
That last one is worth it: a second charge point or a light by the shed is then half a day's work instead of digging again.
Entry into the house
The spot where the cable enters the house is the spot where water later gets in if it is done sloppily. Drill with a slight slope outwards, seal the lead-through watertight and let the cable hang with a drip loop.
And if there is already a cable
Sometimes there is an old supply to the shed or garage. It is usually too light for an EV charger, but can be useful as a draw wire or as a second route. I always test what is there before I pull anything new; that sometimes saves half a day of digging.
What the whole thing then costs depends mainly on the metres. The connection itself starts at € 1.815 including VAT; I always list the extra work for cable and digging separately in the quote, so you can see what it comes down to.
From my own work
At a farmhouse in Ulestraten the desired charging spot was 42 metres from the meter cupboard. With 2.5 mm² the voltage would drop so far at the end that the charger would throttle back. It became 5 x 10 mm² in a duct, with a draw pit halfway. More expensive in material, but the charger now simply delivers its full power and a second point can be added later.
When to call an electrician
- The charging spot is more than fifteen metres from the meter cupboard
- A driveway or garden has to be crossed
- You later want a second charge point or an outdoor kitchen on the same cable
I calculate the cable for length and power before anything goes into the ground. Request a quote.
Frequently asked questions
Can I use an existing cable to the shed?
Usually not, because it is too light for an EV charger. But I do test it, because sometimes it is usable as a draw wire or for a second purpose.
How deep does a buried cable need to be?
At least 60 cm under a garden and deeper under a driveway where cars drive, with sand around it and a warning tape above it.
Why do you always recommend an empty duct?
Because a second charge point, a camera or a light by the shed then just means pulling a cable through instead of digging again. During the work that duct costs next to nothing.
Further reading
EV charger at home: single-phase or three-phase, and which protection
The choice depends as much on your car as on your connection. With the costs, the RCD debate and why load balancing is not an optional extra.
Load balancing: why your main fuse can cope after all
Without load balancing the car keeps charging at full power while the oven and the tumble dryer are on too. With load balancing the car automatically charges more slowly.
Which RCD protection belongs with an EV charger
An EV charger can produce a DC fault that an ordinary RCD is blind to. It needs protection that can see it.
Questions and comments
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