ACB Vs MCCB

[Eng.mohammed alqaissi]

بسم الله الرحمن الرحيم
الحمدلله والصلاة والسلام على رسول الله وعلى آله وصحبه أجمعين :
الفرق بين ACB & MCCB

The basic difference between MCCB (Moulded case circuit breaker) and ACB(Air circuit breaker) :

The basic difference between MCCB (Moulded case circuit breaker) and ACB(Air circuit breaker) is that the former can not be closed remotely because the operating mechanism of MCCB is different from the ACB. Secondly, MCCb is not repairable and complete unit is required replacement while ACB can be repaired. AS far as tripping system is concerned both can have instantaneous as well as time graded tripping device. It can be magnetic, thermal and electronic also. Construction wise ACB is more robust.. It also has instantaneous and overload tripping devises, but these setting are fixed i.e. factory set and can not be changed.
More information you can have from the manufacturer's catalogue.


A major difference is that most MCCB are 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 to 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.

I agree with the above postings. The Master pact does have withstand ratings required per ANSI C37.13. That allows the Master pact frame to be used for either UL489 or ANSI C37.13 applications. Notice the ratings on the last page of each of these links however. The UL489 version shows an "Instantaneous override" pickup value and the ANSI version does not.


Notice the UL489 version is called "insulated case circuit breaker", and the ANSI version is called "low voltage power circuit breaker".

UL489 circuit breakers (MCCB/ICCB) are for use in UL891 rated "switchboards", whereas ANSI rated circuit breakers (ACB) are for use in ANSI C37 "low voltage power switchgear"
This discussion applies mainly to U.S. standards.

[د/ هاني احمد عبد السلام]

Thank you for this effort
What about the British Standards?