Charging with a 3-pin plug: is it enough?
Will a 3-pin plug (a "granny charger") keep up with your driving, can it charge in your tariff's cheap hours, and what would a 7 kW wallbox save you a year? Pick your car, your miles and your tariff.
Calculator
Does a 3-pin plug keep up?
| Charger | Miles a night | Miles a week | Time to add a day's miles |
|---|---|---|---|
| 3-pin plug2.3 kW | 88 miles Derived 2.3 kW × 0.86 charging efficiency = 1.98 kW into the battery, × 12 hours parked = 23.7 kWh, × 3.72 miles per kWh (the car's official (WLTP) figure). Sources
| 618 miles Derived 88 miles a night × 7. Sources
| 3 h 32 min Derived 6.99 kWh a day ÷ 1.98 kW into the battery. Sources
|
| 7 kW wallbox7.0 kW | 284 miles Derived 7.0 kW × 0.91 charging efficiency = 6.37 kW into the battery, × 12 hours parked = 76.4 kWh, × 3.72 miles per kWh (the car's official (WLTP) figure). Sources
| 1,990 miles Derived 284 miles a night × 7. Sources
| 1 h 06 min Derived 6.99 kWh a day ÷ 6.37 kW into the battery. Sources
|
You need 26 miles a day, 182 a week: 7.0 kWh Derived 26 miles ÷ 3.72 miles per kWh (the car's official (WLTP) figure). Source
Can you charge inside the cheap window?
A 3-pin plug needs 3 h 32 min a night on EDF GoElectric (cheap rate 6.66p for 7.0 hours a night), so 100% of its charging gets the cheap rate. A smart wallbox needs 1 h 06 min a night on Octopus Energy Intelligent Octopus Go (cheap rate 7.60p for 6.0 hours a night), so 100% of its charging gets the cheap rate.
This assumes your car is plugged in during the cheap hours: the hours parked you entered are overnight.
Cost a year on this tariff
3-pin plug, on GoElectric
£198 Estimated 6.99 kWh a day ÷ 0.86 charging efficiency × 365 = 2,966 kWh a year from the wall, × 6.66p on EDF GoElectric (100% at the cheap rate). Sources
7 kW smart wallbox
£213 Estimated 6.99 kWh a day ÷ 0.91 charging efficiency × 365 = 2,803 kWh a year from the wall, × 7.60p on Octopus Energy Intelligent Octopus Go (100% at the cheap rate). Sources
A wallbox costs more
£15 a year Estimated The 3-pin cost minus the wallbox cost: a wallbox wastes less energy as heat and fits more of the charging into the cheap rate. Sources
Payback
On these figures a wallbox doesn't save money on energy, so it won't pay for itself: its benefit here is speed.
Safety: Use the car maker's own charging cable, plugged straight into a suitable household socket. Never use an extension lead, cable reel, power strip, adapter or timer. (CUPRA Born owner's manual (UK, March 2026), p.92, Charging)
3-pin plug or wallbox: how it works
A 3-pin charging cable is limited to 10 amps: 2.3 kW. A home wallbox gives 7 kW on a normal single-phase supply, about three times as fast, as long as the car can take it. More of a wallbox's power reaches the battery: in published tests about 86% of the electricity from a socket ends up in the battery, against about 91% from a wallbox.
The bigger difference is usually the tariff. EV tariffs are cheap for a few hours a night, or only for charging the supplier schedules through a compatible smart charger or car. A slow 3-pin cable may not fit a night's charging into those hours, and the rest is charged at the day rate. How we work it out.
Electricity rates are the suppliers' published headline rates, checked 12 October 2026. Your own rates depend on your region.
3-pin charging: questions
Can you charge an electric car with a 3-pin plug?
Yes, with the charging cable that came with the car, plugged straight into a household socket. At 2.3 kW it adds about 7 miles an hour to a Renault Scenic E-Tech, against about 24 on a 7 kW wallbox. Overnight, that's often enough for a normal day's driving.
How long does it take to charge an EV with a 3-pin plug?
Slowly: about 27 hours to take a Renault Scenic E-Tech from 20% to 80% (53.4 kWh). A 7 kW wallbox does the same in about 8 hours.
How much does it cost to charge an EV on a 3-pin plug?
About 8.2p a mile at the Ofgem price cap rate (26.32p per kWh), or about 2.1p a mile at EDF GoElectric's cheap rate (6.66p) if the charging fits in its window. That tariff is open to any EV, including one charged from a 3-pin plug. That's for a Renault Scenic E-Tech at 3.7 miles per kWh.
Granny charger vs wallbox: which is cheaper to run?
A wallbox. A 3-pin cable loses more energy as heat (we use 86% efficiency against 91% for a wallbox, from published tests), so it uses about 6% more electricity for the same miles. And on an EV tariff a slow cable often can't fit a night's charging into the cheap hours. Whether that pays for a wallbox depends on your miles: the calculator above works it out.
Is it safe to charge an EV from a 3-pin plug?
Yes, if you do it the maker's way. Use the car maker's own charging cable, plugged straight into a suitable household socket. Never use an extension lead, cable reel, power strip, adapter or timer. (CUPRA Born owner's manual (UK, March 2026), p.92, Charging.)