Fuse testing according to the IEC 60269-4: 2009 includes verification of the breaking capacity. The breaking capacity of a fuse is the maximum available current, at the rated voltage that the fuse can safely open without  creating any hazard. After the test the fuse-link and fuse holder combination  is checked for i.a. mechanical damages, welding, burning or ignition and significant movement of the end caps.  In practice;  is it possible  to  replace the fuse safely. 

Although fuses are designed to open a circuit to protect conductors and devices against over-currents, they do not all do it in the same manner. For example, fuses to protect sensitive devices that are designed to open very quickly and allow a minimum amount of energy during an over-current to go through or a motor protection fuse which is designed to withstand large in-rush currents in multiple start-up situations. Some fuses only protect against short circuits(back up) when others also protect against overloads.

Some challenging problems Damstra Laboratory faced  when  testing slow` fuse breaking capability against a modest overload current. The existing test arrangement does not permit the overload current to be maintained at operational  voltage during the total required testing time.  To overcome this, Damstra laboratory has developed a reliable method to pre-heat the fuse by using an external D.C. current source. During this pre-heating, the voltage over the fuse is being monitored. The timers of Damstra Laboratory allow reliable monitoring and trigger instance change over to the AC test circuit at operational voltage as soon as it register a change in the resistance of the fuse element. This ensures that the fuse is connected to the test circuit with required circuit characteristics just before  the moment  the arc is initiated.