The overload breaker and the meter
The overload circuit breaker
The supply first passes through the overload circuit breaker fitted in the live wire. It is set for a maximum of about 40 A; a larger current trips it, and lifting its lever reconnects the supply. Older circuits used a service fuse instead: a thin lead–tin alloy wire in a porcelain holder that melts when the current is too large.
Either one disconnects only the live wire.
The electricity meter
The consumer is charged for the energy used, which the meter records in kilowatt-hours (kWh). The live and neutral from the overload breaker go into the meter, and out of it to the isolator.
Figure to be added
They belong to the supplier
The overload breaker and the meter belong to the supplier (the Electricity Board or company). If there is a fault with them, tell the supplier to fix it.