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Start by
Sokun Nhoem
08-30-2014 03:39 AM

When do we use MCCB and when we use MCB?

Could anyone tell me when do we use MCCB and when we use MCB? What are the differences between their basic function?RegardSokun
08-30-2014 05:53 AM
Top #2
Shabib Ghasemi
08-30-2014 05:53 AM
Hello Sokun
MCCB means Molded Case Circuit Breaker and is a breaker that has setting for nominal current,over current whith time and without time .it has rating until 1000A.it uses in systems that have hi short circuit current.MCB means Miniature Circuit Breaker and uses in lighting and... .protect only overcurrent and rating is up to 100A.
it has low short circuit current.
08-30-2014 08:05 AM
Top #3
Paul Best
08-30-2014 08:05 AM
Hi the way to answer this question correctly would depend upon the application..please look on the IEE website, you will also find calculations for the correct size of device.
08-30-2014 10:36 AM
Top #4
Sokun Nhoem
08-30-2014 10:36 AM
Yeah, thanks much for your answer, now I got clearer. By the way, I still have one more wonder why more than 1000A mostly ACB (Air Circuit Breaker) is used instead MCCB?

08-30-2014 01:18 PM
Top #5
shashi bhargava
08-30-2014 01:18 PM
Precisely, Mr Paul Best's answer is OK, but as a thumb rule for domestic purpose for lighting distribution it is MCB normally with lower breaking / rupturing capacity system. MCCB in all Motor and Power distribution Feeders and circuits with higher breaking / rupturing capacity system.
08-30-2014 03:51 PM
Top #6
Masoud Nezami
08-30-2014 03:51 PM
what is MCCB
08-30-2014 06:01 PM
Top #7
Cornwell Takawira
08-30-2014 06:01 PM
Masoud - Moulded Case Circuit Breaker.
08-30-2014 08:44 PM
Top #8
K A Radhakrishnan
08-30-2014 08:44 PM
In the world of Circuit Protection Devices, we use lot of abbreviations and acronyms that sometimes leave everyone with confusion because they may be different from what they have been taught or picked up along the way. A brief description follows to help untangle some of the confusion. I may be wrong somewhere but plese correct me.
To begin with , I am using two terms that need a little definition: "NEMA world" refers to North America, i.e. USA and Canada (and to a lesser extent, Mexico) where standards are developed by NEMA (National Electrical Manufacturers Association) and acceptance testing is done by UL. "IEC world" basically refers to most of the rest of the world that adheres to the standards put forth by the International Electotechnical Commission, who's manufacturers generally self-regulate and test. I will start off randomly and eventually reorganize it in alphabetic order.

MCB In NEMA world, this used to exclusively mean "Main Circuit Breaker", meaning the primary circuit breaker in a group or panelboard / switchboard. In IEC world, it means "Miniature Circuit Breaker", typically a DIN rail mounted circuit breaker in a small format that is limited to 100A, and is intended for use in installations with low fault current capacity (under 25kA) unless protected by upstream fuses. In NEMA world, these devices entered under special rules adopted by UL (UL1077) and are called "Supplementary Circuit Protectors" because they did not meet the criteria already established for "circuit breakers" under UL489. In recent years, many manufacturers have come out with special versions that do now meet the UL489 standards for circuit breakers, so the term MCB has taken on a dual meaning. So in NEMA world, the acronym MCB now has contextual relevance. MCBs / Supplementary Circuit Protectors are sealed units that can be neither maintained or repaired, they are throw-away devices.

MCCB Was originally an IEC term meaning Molded Case Circuit Breaker, but has been very well adopted in NEMA world now, at least at the engineering level. Many rank and file electricians still are not familiar with that acronym because its widespread use in NEMA world is fairly recent. MCCBs generally range from 15A to 1600A, with a few exceptions at either end, and generally start at 14kAIC but go up to 100kAIC for applications with high fault current capacity. There are versions that are Current Limiting (CL) as well. MCCBs are typically sealed units and cannot be serviced, although in larger sizes there are versions with interchangeable parts that can be replaced such as trip units and switch bodies.

MCP A NEMA world acronym for Motor Circuit Protector, specifically describing a magnetic-only MCCB (no thermal trip elements) that is to be used STRICTLY as part of a factory assembled, listed and tested motor starter assembly. They are often mistakenly specified and used in user-built assemblies, but this is not acceptable in the NEC (US) and CEC (Canada). In IEC world, a Motor Circuit Protector can sometimes mean a completely different device, although generally the MCP acronym is not used to avoid confusion. Devices that incorporate Short Circuit (magnetic instantaneous) trips, adjustable thermal (Overload) trips and a disconnecting means, specifically designed for motor loads, is called a Motor Circuit Protector by some manufacturers, a Motor Protective Switch (MPS) by others, a Motor Starter Protector (MSP) by others etc. etc.

I believe I could throw some light into the discussion and clarify to a certain extent.

Radhakrishnan K A
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