The vehicles had eight 6V batteries connected in series giving a typical car 50-mile downhill range and a top speed of around 40/50 MPH. The initial batteries being lead acid (8.8 kWh) could only be charged slowly by a fairly basic on-board charger (approximately 1 kWh in capacity) and take eight hours to fully charge.
As the charging load was very low, it made common sense to use domestic (13 A) plug sockets and this in turn was reflected in the public charging infrastructure.
With the advent of lithium ion batteries with their higher energy density, larger capacity and ability to be charged at a higher rate than lead acid. A more robust charging solution had to be found.
The result was “Mode 3” charging (EN61851-1) with control and safety measures included.
To work with the then public infrastructure and home charging, cars were initially supplied with what euphonically known as “magic cables” in that they had a dedicated EV connector at one end and a 3-pin plug at the other. In the middle was a control box which communicated with the car giving a level of protection and limited the power delivered to 10 A (2.4 kWh). This is close to the maximum power a 3-pin plug can handle. In addition, it must be considered to fully charge even a small electric car will take over 11 hours.
The socket in the garage could be an unknown and at worst be simple spur from another circuit, thus leading to potential overloads. In addition, the power delivered to charge an electric car is in excess for the majority of extension leads, causing the latter to heat up and potentially cause a fire.
As the majority of cars are now supplied as standard with true mode 3 cables and the end to end safety measures this provides. Should you have a “magic cable” with a 3-pin plug, at least one car manufacture is now saying it should only be used for emergencies.