Frequently Asked Questions(MCCBs)
Q1.What are the advantages of MCCBs as a back-up protective device?
Q2.Do MCCBs have short time withstand rating?
Q3.What is utilization category & what category is assigned to MCCBs?
Q4.Are MCCBs suitable for DC applications?
Q5.What types of protection is offered by MCCBs in an installation?
Q6.How many short circuits faults can an MCCB clear?
Q7.When should an MCCB be replaced,i.e. after clearing how many short circuits faults?
Q8.What are the applications in which MCCBs can be used?
|Q1.What are the advantages of MCCBs as a back-up protective device?|
MCCBs offer the following advantages :
|Q2.Do MCCBs have short time withstand rating?|
|MCCBs are downstream protective devices, and hence are expected to sense & clear circuit faults instantaneously without any delay. For this reason, MCCBs do not need to have any shortime withstand rating. However, MCCB's of ratings 1000A & above are also available with short time withstand rating.|
|Q3.What is utilization category & what category is assigned to MCCBs?|
|Switchgear standard IS13947 (part2) / IEC 947-2 has defined two types of utilization category type "A" & type "B".Circuit beakers which are intended to be used for selective tripping (i.e offering time dicrimination with downstream devices) are assigned utilization category "B".Air Circuit breakers(ACBs) fall in this category.Products with utilization category "B" must have a short time withstand rating (Icw).|
|Q4.Are MCCBs suitable for DC applications?|
|Yes, MCCBs with thermal-magnetic releases are suitable for DC application. The thermal rating in these MCCBs remain unchanged.However MCCBs with static or microprocessor based release are not suitable for DC applications.|
|Q5.What types of protection is offered by MCCBs in an installation?|
|Standard MCCBs offer overload and short circuit protection to an installation. However, accessories are available to enable an MCCB to offer earth fault, earth leakage and undervoltage protection as well.|
|Q6.How many short circuit faults can an MCCB clear?|
As per standard IS 13947 (part2) / IEC 947-2, an MCCB can clear following nos. of short circuit faults:
At fault current = Icu(claimed),2 nos. of S.C. faults
At fault current = Ics(claimed),3 nos. of S.C. faults
|Q7.When should an MCCB be replaced,i.e after clearing how many short circuit faults?|
When a MCCB clears short circuit faults,it results in
|Q8.What are the applications in which MCCBs can be used?|
MCCBs can be used in wide ranging applications.Most common usage of MCCBs are in the following applications: