ACB and MCCB both are used for safe making and breaking of electrical systems. In principle, both serve the same purpose.

ACBs are usually seen on upstream side of circuit & MCCBs on load side control (usually, load side switching operations are more frequent than upstream). Depending upon the operating voltages and level of protection(Fault Level) needed for the system ,these three protection device are selected. 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.

MCCBs:
Rated current up to 3200 A.
Adjustable tripping thresholds.
Magnetic or thermal-magnetic operation.
Trip units can be magnetic, thermal-magnetic or electronic.
Most MCCBs have utilisation category "A".
MCCBs in general are less expensive than ACBs.

ACBs:
Rated current up to 6300 A.
Adjustable tripping thresholds.
Thermal-magnetic operation. Trip units can be thermal-magnetic or electronic.
Most ACBs have utilisation category "B" which means that it has an "Icw" value which is the rated short-time withstand current.
ACBs are more expensive than MCCBs.

As for the difference between Compact NS and Masterpact NT/NW, please find below a quick glimpse on the differences between Compact NS and Masterpact NT.

1. Breaking capacities of Masterpact in general are higher than those of Compact NS as illustrated in the attached catalogue extracts (refer to Masterpact Specs.pdf & Compact NS Specs.pdf)
2. Masterpact ACBs have an option of adding a motor mechanism at any time of the lifetime of the product while Compact NS should be ordered from the beginning as an electrically operated device (with motor) or a manually operated device (with the standard toggle). Adding an motor to a manually operated Compact NS device is not possible as it offered as a factory installed model only.
3. Compact NS (>1600A) do not have the option of having a motor mechanism. This option is only valid for Compact NS (from 630A up to 1600A).
4. Masterpact can use a trip unit that measures Harmonics and is meant with power quality and waveform capturing (Micrologic H) and this trip unit is not available for use with Compact NS as illustrated in the attached documents (refer to Masterpact Micrologic Trip units.pdf & Compact NS Micrologic Trip units.pdf).
5. Masterpact auxiliaries section is easier to access. User does not have to trip the breaker and remove its cover (as in Compact NS) to add/remove a certain auxiliary as illustrated in the attached images (refer to Compact NS MCCB.jpg & Masterpact ACB.jpg)
6. Masterpact has a place for adding extra features/auxiliaries such as MCH (motor mechanism), XF (opening voltage release) and PF (ready to close contact) as illustrated in the attached document (refer to Compact NS Electrical Diagram.pdf & Masterpact NT and NW Electrical Diagrams.pdf)
7. Compact NS has restrictions in mechanical and electrical interlocking. These restrictions are not applied to Masterpact NT.

All the above mentioned points of comparisons are valid for Masterpact NW. The one main advantage in Masterpact NW is that it can operate up to 6300A (Masterpact NT operates up to 1600A and Compact NS operates up to 3200A)

The latest version of the Compact NS and Masterpact catalogues can be downloaded through the following direct links:
Compact NS: https://download.schneider-electric.com/files?p_enDocType=Catalog&p_File_Name=LVPED211021EN.pdf
Masterpact NT/NW: https://download.schneider-electric.com/files?p_enDocType=Catalog&p_File_Name=LVPED208008EN.pdf

Released for:Schneider Electric South Africa