This part of IEC 871 applies to internal fuses which are designed to isolate faulty capacitor elements, in order to allow operation of the remaining parts of that capacitor unit and the bank in which the capacitor unit is connected. Such fuses are not a substitute for a switching device such as a circuit-breaker, or for external protection of the capacitor bank or any part thereof. The object of this part of IEC 871 is to formulate requirements regarding performance and testing and to provide a guide for co-ordination of fuse protection.