Many electrical appliances connected to the mains supply use a three-core cable, which includes a ground (earth) wire. However, some appliances are designed with 'double insulation' and only require a two-core cable.
What explains why a double-insulated appliance does not need a ground (earth) wire?
The external casing is made of an electrical insulator, so it cannot become live if a fault occurs.
It operates with a much lower current, so there is no risk of overheating.
A built-in circuit breaker replaces the need for any grounding safety connection.
The live wire is entirely replaced by a secondary neutral wire for safety.
135 exam-style questions on CIE IGCSE Physics Electrical safety, covering Electrical safety. Each one has a worked solution and a mark scheme showing where the marks go.