If your EV charger and your car are a long way apart, whether across a courtyard, over a pavement, or at the far end of a communal car park, a standard 5m or 7.5m cable simply will not reach. A long EV charging cable of 15m, 20m, or even 25m solves that problem, but length brings physics into the conversation: the longer the cable, the more resistance in the conductor, and the more voltage you lose before the electricity reaches your car. Here is what you need to know before you buy.
When do you actually need a cable longer than 10m?
Most UK driveways are served comfortably by a 5m cable, and a 7m cable handles most garages set back from the parking spot. If you are still with us, your situation is probably one of these: a wall charger mounted in an outbuilding at the far end of a courtyard, a communal charger in a car park where the nearest bay is not the closest to the unit, or, most commonly, no driveway at all.
A meaningful proportion of the customers who call us about long cables are flat-dwellers or on-street parkers. You can read more in our dedicated piece on charging an EV without a driveway, but the short version is this: if your charger is at a pavement post, a lamp-column socket, or a building facade outlet across a footpath and a parking bay, you are looking at 10-15m of cable before the car connector even enters the picture. Factor in the arc the cable takes around the car and 15m can easily become the minimum, not a luxury.
For those situations, our full EV cable length guide lays out a decision tree based on driveway depth, building position, and charger mounting height. But the guide stops short of the long-cable physics, and that is where this article picks up.
If you are still deciding whether a 10m cable is enough for your setup, start there before committing to the extra weight and cost of a 15m or longer run. And if you are not sure which cable type your car needs at all, our guide on choosing the right EV charging cable covers connector types and compatibility across all current UK models.
Voltage drop explained: the maths behind long cable runs
Every metre of copper conductor adds resistance, and resistance converts electrical energy into heat instead of delivering it to your car’s battery. At short cable lengths this loss is negligible. At 25m it demands careful thought about conductor sizing.
The formula is: ΔV = (2 × L × I × ρ) / A
Where: - L = cable length in metres - I = current in amperes (32A for a 7.4kW charger) - ρ = resistivity of copper = 0.0168 Ω·mm²/m - A = conductor cross-section in mm² - The factor of 2 accounts for both the live and neutral conductors
BS 7671:2018+A2:2022 (IET Wiring Regulations), Section 722, the governing standard for EV charging installations in the UK, permits a maximum voltage drop of 3% on consumer circuits. At 230V supply, that is a ceiling of 6.9V across the full cable run.
Understanding how amps relate to power output is worth a moment’s reading in our explanation of amps and kilowatts in EV charging, and if you are weighing up 16A versus 32A charging on longer runs, the 16A vs 32A charging cable comparison adds useful context.
- X-axis: [5, 10, 15, 20, 25] (metres)
- Series 2.5mm² (avoid): [0.58%, 1.17%, 2.80%, 3.74%, 4.67%]; #EF4444
- Series 4mm² (marginal): [0.37%, 0.73%, 1.75%, 2.34%, 2.92%]; #F59E0B
- Series 6mm² OFC (recommended): [0.24%, 0.49%, 1.17%, 1.56%, 1.95%]; #22C55E
- Reference line BS 7671 max 3%: horizontal dashed at y=3.0; #EF4444
- Point labels: ΔV in volts at 15m, 20m, 25m for all three series
The table below puts the calculated numbers side by side so you can see exactly where each conductor falls at each length:
| Conductor | 15m ΔV | 15m % | 20m ΔV | 20m % | 25m ΔV | 25m % | 25m verdict |
|---|---|---|---|---|---|---|---|
| 2.5mm² | 6.45V | 2.80% | 8.60V | 3.74% | 10.75V | 4.67% | FAIL |
| 4mm² | 4.03V | 1.75% | 5.38V | 2.34% | 6.72V | 2.92% | MARGINAL |
| 6mm² OFC | 2.69V | 1.17% | 3.58V | 1.56% | 4.48V | 1.95% | PASS |
All figures calculated at 32A (7.4kW single-phase), copper resistivity ρ = 0.0168 Ω·mm²/m. Percentage of 230V nominal supply.
- as per the markdown table above: 2.5mm² / 4mm² / 6mm² OFC at 15m, 20m, 25m; all nine ΔV and % values; verdict badges
The 4mm² result at 25m, 6.72V or 2.92%, is technically within the 3% limit, but it sits so close to the edge that any contact resistance at the connector (from a slightly dirty or worn socket) can push it over. We treat 4mm² as non-compliant for 25m use in practice.
Why 6mm² OFC copper is the minimum for 32A at 25m
At 32A over 25m, a 6mm² OFC conductor produces a voltage drop of 4.48V, or 1.95% of the 230V supply, comfortably within the 3% limit set by BS 7671:2018+A2:2022 (IET Wiring Regulations), Section 722. Step down to 4mm² and the drop rises to 6.72V (2.92%), right at the edge of compliance. Drop to 2.5mm² and you are at 4.67%, out of tolerance and a source of excessive heat in the conductor itself.
Those numbers answer the “what cross-section” question. The “what conductor material” question is answered by the distinction between OFC and CCA.
OFC, or Oxygen-Free Copper, is the conductor to specify for any long EV cable. Copper-Clad Aluminium (CCA) cables carry a higher resistance per mm² than pure copper, meaning voltage drop is worse at any given cross-section. More critically, aluminium is brittle at repeated flex points. A 25m cable is picked up, uncoiled, and plugged in every charge cycle; CCA sheaths crack at the bends over time, OFC does not.
CCA cables are cheaper to manufacture and sometimes marketed without clearly naming the material. The tell is the weight: a genuine 6mm² OFC cable is noticeably heavier than a CCA equivalent of the same stated cross-section, because OFC copper is denser. If a long cable feels unusually light for its size, ask the supplier for the material specification in writing.
For a deeper dive into conductor materials and what gauge markings actually mean, our guide to OFC copper and cable gauge covers the subject in full.
15m vs 20m vs 25m: which length do you actually need?
15m cables
A 15m cable is the sweet spot for most long-reach situations. It is the right choice when: your charger is in an outbuilding set 10-12m from the parking spot, you park in a communal bay where the charger post is at the opposite end of a row, or you live in a terrace with a pavement socket and your car parks at a slight distance from the outlet.
At 32A and 6mm², a 15m cable drops only 2.69V, or 1.17%, so you have plenty of headroom. The weight is manageable: roughly 2.5-3 kg for a 32A 15m assembly. Most standard charger cable holsters handle this without complaint.
20m cables
Twenty metres suits situations where 15m falls just short: a wider courtyard, a longer vehicle (SUVs and vans need more cable to reach the inlet), or a parking bay where the car cannot always be positioned close to the outlet. At 6mm², 20m produces a 3.58V drop (1.56%), still comfortably inside the limit.
Weight climbs to roughly 3-4 kg at this length. Begin thinking about how you will carry and store the cable, because daily handling of a coil this heavy becomes a minor ergonomic event.
25m cables
Twenty-five metres is the longest cable we recommend for regular domestic and on-street use. It is appropriate when the gap between charger and car is genuinely large: a shared car park where the EV charging bay is positioned at the far end, or a commercial courtyard where the charger is wall-mounted well away from visitor parking.
A 25m 32A cable can weigh 4-5 kg. That is the weight of a bag of flour plus a bag of sugar. You will feel it after a week of daily plug-in cycles. Check that your charger’s cable bracket or holster is rated for that load. Many are not.
Our cable length recommendation guide includes a measurement methodology that helps you confirm the exact run before ordering.
Handling a long heavy cable: weight, strain relief, and storage
Strain relief at both ends
Strain relief, the reinforced section where the cable exits the connector housing, is more important on a long, heavy cable than on a short one. The weight of 4-5 kg of cable hanging from a connector puts constant downward tension on the internal wire terminations. Over hundreds of plug-in cycles, that load works the conductors against their terminations and causes fatigue cracking at the gland.
When evaluating a long EV cable, check that the strain relief boot is robust and extends at least 80-100mm back from the connector body on both the Type 2 socket end and the plug end. A stiff, well-engineered boot distributes the bending load over a longer section of cable rather than concentrating it at a single flex point. This is the single component that differentiates a cable built for long-term daily use from one built to a price.
If you are concerned about connector security on public posts, our article on EV charging cable locks and theft prevention covers supplementary security options that also reduce connector movement, which indirectly helps strain relief.
Storing a long cable safely
The safest storage method for a long EV cable is the figure-8 coil: alternate the direction of each loop so the cable lies flat without twisting the TPU outer sheath. With each loop reversed, the accumulated twist from one direction is cancelled by the next, leaving the cable lying in a flat, tangle-free coil that unwinds cleanly at the next session.
Avoid tight drum-style coils, because the inner loops are under constant compressive bend stress. Over time, the TPU sheath develops permanent set and eventually micro-cracks at the tight inner radius. A reel with a wide hub (minimum 150mm diameter) distributes the bend radius gently enough to avoid this; anything smaller is effectively the same problem as a tight drum coil.
Never store a long cable in a tight bundle inside a boot bag. The random kinking that results from pulling a bundled cable out under tension is the quickest way to damage the sheath and introduce flex stress at unpredictable points.
A final practical note: never leave a 25m cable coiled while charging. At 32A, a coiled cable generates heat in the coil that cannot dissipate. Always fully uncoil before beginning a charge session, then store correctly afterwards.
Frequently asked questions
What is the longest EV charging cable available in the UK?
Twenty-five metres is the longest Type 2 EV charging cable you will find from reputable UK suppliers for regular use. At that length, conductor cross-section becomes critical: you need at minimum 6mm² OFC copper running at 32A to stay within the 3% voltage-drop limit set by BS 7671:2018+A2:2022 (IET Wiring Regulations), Section 722. Longer cables exist for industrial EV fleet applications but are outside normal domestic and on-street scope.
Will a 25m EV cable charge my car more slowly?
Not noticeably, provided the cable is correctly rated. A 6mm² OFC cable at 25m drops only 4.48V at 32A, or 1.95% of the 230V supply, which is well within tolerance, and your car’s onboard charger will not reduce current in response. An undersized 2.5mm² cable, however, drops 10.75V (4.67%), and the car’s onboard charger will detect the reduced supply voltage and throttle charging current to compensate, making the session slower and generating unnecessary heat in the cable.
Can I use a 15m EV cable with a standard 3-pin plug?
A 3-pin EVSE granny cable is limited to 10A or 13A for safety reasons, and most have a built-in current limiter set lower still. At 13A over 15m, even a 2.5mm² conductor produces around 2.6V drop (1.13%), which is technically within limits, but the slow charge rate (around 2.4kW at 10A) makes a 15m run difficult to justify for regular use. For any 15m+ deployment, a dedicated Type 2 wall charger at 16A or 32A is far more practical.
Is it safe to leave a long EV cable coiled while charging?
No. A coiled cable running at 32A accumulates heat in the interior of the coil, where airflow is restricted. This is particularly significant with a 20m or 25m cable because there is more conductor surface area generating resistive heat and more coil mass trapping it. Always fully uncoil the cable before beginning a charge session. After charging, re-coil using the figure-8 method to prevent TPU sheath kinking.
What does IP55 mean for a long cable used on-street or in wet conditions?
IP55 means the cable is protected against particulate ingress and water jets from any direction, covering rain, puddles, snow, and typical UK outdoor conditions. It does not mean the cable can be submerged or left in standing water. For on-street use across pavements or in open parking areas, IP55 is the minimum rating you should accept. IP67 or higher offers additional submersion tolerance if your cable regularly sits in gutters or poorly drained surfaces.
Why is CCA (Copper-Clad Aluminium) a problem specifically in long EV cables?
Two reasons. First, CCA has higher electrical resistance per mm² than solid OFC copper, so voltage drop at any given cross-section is worse. Second, and more damagingly, the aluminium in CCA is brittle at repeated flex points. A 20m or 25m cable is coiled, carried, and uncoiled daily; the flex points accumulate mechanical fatigue. OFC copper is ductile and resists this indefinitely under normal use. CCA conductors can crack internally at the sheath bends without any external sign, creating a hazard that is invisible until the cable fails or overheats.
How do I check if my charger bracket can hold a 25m cable?
Check the bracket’s stated maximum cable weight in the installation manual or on the manufacturer’s product page. Many standard Type 2 charger holsters are rated for cables up to 2-3 kg. A 32A 25m cable with 6mm² OFC conductors and a full TPU jacket typically weighs 4-5 kg, enough to exceed that rating. If your bracket cannot handle the weight, the cable hangs permanently under tension at the connector gland, accelerating internal conductor fatigue at exactly the most vulnerable point.