MCB And MCCB Circuit Breakers

Have you looked at http://en.wikipedia.org/wiki/Circuit_breaker#Other_breakers

I was going through this discussion, I need information on co-ordination between MCB and BCCB feeder.

I have a main board with MCCB outgoing feeders (Incomer for this is ACB and bus bar rating 27kA) . There is a subdistribution board (i.e. BMK in field substation) which is taking feed from the main board. This BMK has incomers and outgoing feeders as MCB.

Now question what will be the fault current seen by my sub distribution board (BMK), as MCB is used it should be less than or equal to 10kA. Can anybody throw some light on this topic?

MCCB & MCB are basically electrical switch gears through which- At normal conditions, you can make or break electrical circuits & At abnormal conditions like short circuit, overload, earth fault, it automatically breaks the circuit safely.

MCCB is used for High rating & gets tripped if any over load, short circuit or earth fault happens. Tripping facilities depends on the inbuilt trip functions which you select while procuring the MCCB.

MCB is used for for low rating & gets tripped if any short circuit happens.

Regards,

Vinod.P (vinod29mar@gmail.com),

apart from that the significant difference is MCB (Miniature Circuit Breaker) Trip characteristics normally not adjustable, factroy set but in case of MCCB (Moulded Case Circuit Breaker)—Trip current field adjustable.

Hi..

Could u please explain me what are the charecteristics that we can change in MCCB and which we could not change in MCB.

Its (1) Rated Current to increase breaking capacity and (2) Instantaneous Current-This function allows users to directly adjust an instantaneous trip current.

thanks

Is the rating current of MCB below 100A?

When the proximity switches should be used?

How I can calculate the main frame breaker for distribution panels, and what is the differance between it and main trip beaker?

I am sorry for inconvenience?

In most of the world, MCBs are for small loads and residential applications where the available fault current is low, as in 5kA or less. MCCBs are used when the available fault current is higher. If you do not understand what available fault current means, you have no business being the one to select which type to use.

If you are in the US, the differences are greater. Most MCBs are not UL listed as circuit breakers, they are called "supplementary circuit protectors" and cannot be used in the same way as circuit breakers; they must have either a real circuit breaker or fuses ahead of them and the let-through current must be below 5kA. There are new versions of these devices that have attained UL489 listing as "circuit breakers" and can withstand 10kA or slightly more, but they are now called UL489 MCBs, not just MCBs, and they are slightly larger and more expensive.

Explanations are OK. However the following may also be noted.

MCB - Miniature Circuit Breaker

MCCB- Moulded Case Circuit Breaker

R.Thiyagarajan

^5

macchan u r very brillient

i want to known the exact different between MCB and MCCB

I believe the exact differences are as follows:

1. MCCBs generally have an adjustable overcurrent trip setpoint whereas MCBs generally do not.
2. MCCBs have a fault interrupting rating of >10K amps whereas as MCBs are generally limited to 10K amps max fault interrupting current
3. MCCBs can be obtained with just a magnetic (instanteneous) trip function for use in combination motor starters whereas MCBs always have both thermal and magnetic trip functions.

In the US, thermal-magnetic MCCBs (the most common types) are NEVER allowed to have an adjustable overcurrent trip point. Only the instantaneous trip (magnetic) is allowed to be adjustable. Electronic Circuit Breakers are allowed to have adjustable Long-time, Short-time and Instantaneous trips, but they are much much more expensive and not commonly used other than on systems where a qualified engineer has done a Fault Coordination Study.

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