An interface for cutting off the power supply for any fault current Id≦300 milliamperes such that: Id≧IPE+k·Ih where IPE represents the current returning to the power source via the protective conductor connecting the exposed conductive parts to earth and Ih (≦10 or 30 milliamperes) represents the current returning to the power source by ways other than via the protective conductor or via an active conductor. Current Ih is therefore likely to travel through a person. In this way, the interface protects people and property against ground insulation faults and against certain direct contacts independently of the earth of the exposed conductive parts and of external conditions. It also protects people in the event of a failure in the protection of an area using the same earth in case of a fault.