The FZN21-12D indoor high-voltage AC vacuum circuit breaker is suitable for power supply networks with three-phase AC 50Hz and rated voltage of 12kV, used for opening load currents. It is particularly suitable for applications requiring oil-free operation, no maintenance, and frequent operation. The FZRN21-12D indoor high-voltage AC vacuum circuit breaker-fuse combination is also suitable for power supply networks with three-phase AC 50Hz and rated voltage of 12kV, where oil-free operation, no maintenance, and frequent operation are required. This circuit breaker and combination unit have a distinct isolation gap, can be equipped with a grounding blade with closing capability and an electric spring mechanism, and can achieve remote control.