INTRODUCTION
When deciding between a medium voltage vacuum circuit breaker or medium voltage vacuum contactor for your
application, there are many factors to consider. Each device is designed with specific features that allow it to meet
the demands of some applications better than others.
APPLICATION CONSIDERATIONS
Joslyn Clark experts make the following recommendations for when to choose a vacuum contactor versus a
vacuum breaker.
Vacuum Contactors are designed for applications where:
• Typical loads include motors or smaller transformers
• Continuous load current is low or moderate (e.g., Smaller motors or transformers)
• 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 the system.
In contrast, Medium voltage vacuum breakers are better suited for applications where:
• Loads include transformers, capacitors, larger motors, generators, or distribution feeders
• Ratings required exceed those of vacuum contactors (200 A or 630 A at up to 15 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 switch gear bus arrangements
When applied appropriately, both the medium voltage vacuum breaker and vacuum contactor can provide your facility with reliable power switching and optimal service. In instances where the switching device is applied improperly, you may find maintenance costs are higher, and your facility may experience unnecessary downtime.
ADVANTAGES OF VACUUM CONTACTORS VS. VACUUM BREAKERS
Size Advantages
At ~17% the total volume, and ~40% the weight at 7.2kV, vacuum contactors offer a significant size advantage over
vacuum breakers.
Operating Life
At ~10X the mechanical life, and ~10x the electrical endurance at continuous current, vacuum contactors excel in
frequent switching applications.
VACUUM BREAKER VACUUM CONTACTOR
Mechanical Endurance High- typically 10,000 operations Very high, up to 1,000,000 operations up to 630A
Electrical Endurance @ continuous current 10,000-50,000 operations 300,000-1,000,000 operations
Current Chop
When using vacuum interrupters, there is a phenomenon known as “current chop” that can send dangerous
transients down the line. The contact materials used in vacuum contactors help to minimize current chop, thereby
limiting these dangerous transients, whereas vacuum breakers do not. Breakers are designed for higher current
interruption and as a result, have a higher current chop not rated for frequent interruption.
Maximum current chop values of Joslyn Clark contractors are typically 1/10 that of a comparable vacuum circuit
breaker.
JOSLYN CLARK MVC SERIES 7.2KV VACUUM CONTACTOR
• 12.75” Tall
• 14.5” Wide
• 10” Deep
• 56 lbs
TYPICAL 7.2KV VACUUM CIRCUIT BREAKER
• 22.6” Tall
• 20.75” Wide
• 22.5” Deep
• 137 lbs
Medium Voltage Vacuum Circuit Breaker Vs Medium Voltage Switch Fuse Unit
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) The 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 are needed).
Process continuity is compatible with fuse replacement time Reduced-voltage starting is needed to reduce starting duty and voltage fluctuation on system
