I agree with the previous response - I interpret your i nquiry as what is the difference between an Low voltage Power Breaker (LVPB) and a Molded Case Circuit Breaker(MCCB). LVPB are build to ANSI standards and are listed to UL 1066, MCCB are listed under UL489. I have no idea how the IEC standard distinguishes these breakers The difference is in the testing. The main advantage to the LVPB is the 30 Cycle withstand rating that is a part of the UL 1066 listing. li sting. This breaker can withstand a high short circuit for up to 30 cycles and give a downstream device time to clear the fault. Many designers like to use LVPB as a main ahead of MCCB for this reason. Other designers just incorporate this feature into ther e overall short circuit and coordination study. UL 489 MCCB are not required to undergo this test. Another advantage of the LVPB is it is serviceable. These breakers can be reconditioned with replaceable contacts, arc chutes, and other and parts readily available. The disadvantage of LVPB is they are big and require a lot of space. You vary rarely see them below 800 amps There are so many thing advance future in ACB than MCCB, 1) selection of tripping curves in ACB are (In, Ir, Inst/MCr, ST, LTD, GFT & P TA). 2) Making & breaking time. 3) Ampere rating, Arc chamber, KA rating & etc 4) ACB Acc. more loaded than MCCB. 5) ACB used as a Master Breaker on Incoming Side, and MCCB are used as a feeder Circuit Breakers. 6) ACB Mechanical & electrical life is more than MCCB. And many more advance futures in ACB.
we can distinguish the ACB & MCCB as , 1. ACB due to its time withstanding capacity (Isw) feature ,comes in 'B' category 2.Though MCCB has not Isw feature , i comes in 'A' category. now please refer the below example : We can use both MCCB Or ACB as an incomer for the same rating but for big industries where small load shedding means crores of loss ,there we must use only ACB's . during the course of short circuit ,MCCB's will trip the load instatniously i nstatniously but ACB due to its 'Isw' feature, will hold the Shortcircuiting current for seconds which will be sufficient to go for secondary option .During that course of time a signal may be given to the genset and we may get the continuous supply without loadshedding .
In MCCB we can have only two auxillaries but in case of ACB ,we can have n-number of auxillaries . Moreover MCCB's are not repairable ,where as we can repair ACB's
ACB and MCCB both are used for safe making and breaking of electrical system. In principle both serve the same purpose. Earlier concept was to use OCB/ACB / when large load currents were to be handled because they were very robust and could withstand high making and breaking capacity and allow many frequent safe making and breaking .Due to various fire hazards and high coast of maintenance,the use of OCB in LT distribution is getting eliminated . With technological development a new version of circuit breakers were introduced with moulded case which were initially having only very low load break capacity.They were much cheaper and use and throw type and could be used for only limited number of operations. With further development in technology, the at present day MCCB are designed with larger make and break capacity and fault withstand capacity. As stated by Baby Guinness now MCCB with capacity of 3200 A and breaking capacity of 200KA with all control benefits and dependable quality are available from reputed manufacturers. They need less space in the panel compared to ACB. ACB has robust enclosure, draw out facility, sliding shutters and capacity to withstand many break and break operation with out damage and proven technology. ACB is still preferred for on load switching operation of 800 Amps and higher system For short circuit protection, it is importent to break the circuit quickly - before the current reaches to its prospective peak value, to limit the let through energy & corresponding damage it can casue. In good olden days (before advent of MCCB), this function was being done effectively by fuses on load side. But this was expesive as every time, you need to replace the fuse. ACB mechanism is very heavy - with high inertia, & hence can not break the circuit as fast as fuses. The concept of MCCB was developed to give short circuit protection on load side, by making its mechanism as light as possible - to enable it to beak the circuit very fast - & hence MCCB could replace fuses for giving short circuit protection with least operating cost!! ACBs are usually seen on upstream side of circuit & MCCBs on load side control. (Usually, load side switching operations are more frequent than upstream) As the technology has improved over the period of time, the rating & breaking capacities of MCCBs are increasing - hence there is possibility of overlap in application of ACB & MCCB. As far as replacement of ACB with MCCB is concerned, it is possible - but please take care of proper co ordination with other down stream & upstream switchgear!!
mccb comes in 'A' category according to the IEC and ACB comes in 'B' category . b category means that the breaker which has a ( ICW ) short circuit with stand capacity and a category is vice a versa . which means where we dont want any instantanious tripping , we can use A Cb there because it has a tendency to withstand the fault for a certain period and thus in the meanwhile we gets the time to switch the secondary supply and thus contin uous functioning of the production . Major difference between MCCB and ACB is that ACBs are category B devices where as MCCBs are category A Devices. This means that MCCBs do not haev Icw rating and are not suitable for full discrimination. discrimination up to certain falut level can onl y be achieved with MCCBs.
A major difference is that most MCCB a re designed with a "Blow Open" contact arrangement. The magnetic forces caused by rapid rise of current actually aid in the opening of the contacts under fault conditions, the higher the current the stronger the repulsion. This is why there is no short time with-stand rating for these devices. Even those that have a short time adjustment are difficult to coordinate. If you were t o disassemble one of the inexpensive residential style molded case breaker you will not find a magnetic coil for instantaneous trip. They rely solely on the blow open design. LVPCB (ACB) has the opposite contact design, "Blow Closed". As current rises rapidly the magnetic forces pull the contact surfaces together. This allows the LVPCB to hang in there on a fault for a short period of time before tripping to allow a down stream device to clear and give superior system coordination.
