Twenty metres does not come with a cable size attached. A 7 kW charger is a 32 A-class continuous load — on a 40 A circuit under the NEC’s 125% rule — and the cable for that circuit is calculated by your electrician, not looked up. Distance is one input: voltage is lost along any run, and the loss grows with length and current, so a 20-metre run can push the calculated size up. But length alone never produces a size — cable type, installation method and your local code sit in the same calculation.
Key Takeaways
- A 7 kW charger is a 32 A-class continuous load on a 40 A circuit — and its cable is calculated, not catalogued.
- Distance moves the answer because voltage drop grows with length and current; a 20-metre run can push the size up, but never names it.
- The routed, measured run — not the straight-line estimate — is the input that counts, and it belongs on the quote.
- Position, a subpanel, or a lower setting are the levers when the run is long.
What the Distance Actually Does
Every conductor resists current a little, so voltage is spent along the run — the loss is called voltage drop. Two things make EV charging expose it. First, the drop grows with both current and length: double the run and you roughly double the loss for the same cable. Second, the load is continuous — a charger holds full current for hours, where a kettle holds it for minutes. A run never designed for its length can waste energy as heat and leave the car receiving less voltage than intended; a designed run delivers the charger’s set current as a matter of course. Our orientation guide to wire sizes for EV chargers covers the wider sizing conversation.
The 20 Metres You Measure Is Rarely the Run
Before distance can move any calculation, it has to be the right distance — and the number in the question is usually the wrong one:
| Distance | What it actually is | Who settles it |
|---|---|---|
| The straight line | Panel to parking spot, as the crow flies across the house | You, with a tape measure — a starting estimate only |
| The routed run | The path the cable really takes: up, over, around rooms, out through a wall | Your electrician, at the survey — the measured length belongs on the quote |
| The charger’s reach | The fixed length of the charger’s own lead, mounting point to charge port | The product’s stated specification |
Routed runs are almost always longer, sometimes by a wide margin — and a quote sized off your estimate is built on an input nobody verified.
The Levers When the Run Is Long
If the calculated size comes back larger than you hoped, there are honest levers besides accepting it:
- Shorten the run. Moving the charger, or feeding it from a different point, can cut the routed length more than any other choice — position is decided against where the car parks.
- Bring the panel closer, on paper. A subpanel near the parking area, fed by one designed run, is a standard pattern for long distances — your electrician’s call.
- Start from a smaller current. The calculation begins with the charger’s configured draw; a unit set lower needs less of everything downstream. The trade is charging speed, chosen knowingly.
- Accept the calculated size. Sometimes the right answer is simply the larger cable, once, rather than a compromised circuit for life.
Most 7 kW Chargers Are Plug-In: The Cable Is Behind the Outlet
Notice what none of this asks you to buy. The EV-ACS3210T (about 7.7 kW, NACS, adjustable in six steps from 10 to 32 A, NEMA 14-50P, IP66) and the EV-ACS4005T (9.6 kW, NACS, adjustable 16/24/32/40 A, IP66) are plug-in portables: their leads are fixed parts of the units, and their current steps are exactly the “smaller current” lever above, built in. The cable this article is about is the building wiring behind the outlet — designed for the measured run by the electrician who installs that circuit.
Frequently Asked Questions
Is 20 metres too far for a 7 kW charger?
There is no standard cut-off distance. What changes with length is the design — the calculated cable, the cost — not feasibility: distance is solved in the calculation, not by a limit.
Will a 20-metre run make charging slower?
Not if the run is designed for its length — a correctly specified circuit delivers the set current. The undersized long run is the failure mode: energy wasted as heat, and less than the promised voltage at the car.
Can I just buy the thickest cable available and skip the calculation?
No. The cable must suit the breaker, the charger’s terminals and the installation method as one design — your electrician specifies it for your circuit and run.
Related Reading
- What Size Wire Do You Need for an EV Charger?
- What Size Breaker Do I Need for an EV Charger?
- Where Should You Install a Home EV Charger?
