Medium Voltage circuit breakers are favored when typical loads include transformers, capacitors, larger motors, generators or distribution feeders
(Ratings required exceed those of vacuum contactors 400A or 720 Amp up to 7.2 kV) Continuous load current is high (e.g., larger transformers, larger motors.
Switching is not very frequent (e.g., weekly or monthly):high endurance
(1,000s of operations) is satisfactory Process continuity is critical e.g., no time for fuse replacement Reduced-voltage (RV) starting is not needed (RV starting complicates switchgear bus arrangements)
Medium-voltage NEMA Class E2 controllers fused contactors are favored
when typical loads include motors or smaller transformers continuous load current is low or moderate (e.g., smaller motors or transformer)
Switching is very frequent (e.g., daily or several times per day); very high
endurance (100,000s of operations is needed).
Process continuity is compatible with fuse replacement time
Reduced-voltage starting is needed to reduce starting duty and voltage
fluctuation on system
