ZN28-12 and ZN28A-12 indoor HV vacuum circuit breaker applies to power system of rated voltage 12kV, three-phase AC 50/60HZ. It used to control and protect electric apparatus in industry like mining, substation and so on. ZN28-12 is a unitary type (operation mechanism is installed inside the switchgear and combine with it as a whole); ZN28A-12 is a hanging-on type (the mechanism and switchgear are seperately installed on cubicle or support frame, then connected with link rod and drive shaft.) It conforms to IEC62271-100, GB/T1984, JB3855 and DL/T403 standards.