ABB’s wellknown and fast acting vacuum interrupter and the world’s fastest limiting and switching device, the Is-limiter, have been in service for decades. Now the technologies from these devices have been cleverly combined to form an arc-fault protection system for medium-voltage switchgear that operates in the ultra-fast range. As a product, the extremely short switching time of less than 1.5 ms of this special vacuum device combined with the rapid and reliable detection of fault currents and light intensity of a new dedicated electronic unit, will ensure all arcs are almost immediately extinguished. In technical terms, thismeans that system availability and operator safety are greatly enhanced for rated voltages up to 40.5 kV and rated short-time withstand currents (1s) up to 63 kA. From an economic point of view, downtimes and repair costs resulting from faults will be drastically reduced.