UK’s National Grid warns on electric car home packs

Using rapid chargers at home could trip main fuses, grid operator cautions

Electric car drivers in the UK are unlikely to be able to rapidly charge their vehicles at home at the same time as boiling a kettle, National Grid has warned.

The operator of Britain’s electricity transmission system has cautioned that using a powerful and fast electric car charger at home will trip a main fuse if vehicle owners simultaneously utilise other “high demand” energy items, such as kettles, ovens and immersion heaters.

The warning is contained in a National Grid “thought piece” document which considers some of the potential challenges around the UK’s ambition for a mass rollout of electric vehicles.

National Grid assumes in future most electric cars will need to have a battery capacity of 90 kilowatt hours (kWh) for drivers to make long-distance journeys of about 300 miles.


The ability to travel greater distances without stopping to recharge will be a “must have” if vehicle owners are to abandon their petrol or diesel cars entirely.

An average-size battery charger of 3.5kW would take 19 hours to fully charge a 90kW battery even when it is already 25 per cent full, according to National Grid’s calculations.

A more powerful 11kW device could power up, for example, a Tesla Model S with a 90kW battery in six hours if it was already 25 per cent charged, but owners would be unable to boil their kettles during that time without blowing a fuse, said National Grid.

“The average household is supplied with single-phase electricity and is fitted with a main fuse of 60-80 amps,” added the company.

“If one were to use an above-average power charger, say 11kW, this would require 48 amps. When using such a charger it would mean that you could not use other high-demand electrical items . . . without tripping the house’s main fuse.” – (Copyright The Financial Times Limited 2017)