Miniature circuit Breaker(MCB in IEC world, supplementary protector in NEC) Vs MCCB - Instantaneous 3

[NickParker]

Let's say we have a MCB and MCCB with 16A rating. MCB will trip based on the curve type, say if B curve is used, it trips between 3-5 times the 16A. Therefore, the instantaneous pickup would be anywhere between 48-80A.

This is to decide to use MCB or MCCB. Since this is a project in IEC world, and my counterpart in Europe says always MCB to be used for the final circuit; his argument is that, for the final circuit as the fault current would be lower hence MCB would trip and for MCCB it would not, as the instantaneous pickup will be greater than the fault current.

We always used MCCB for the final circuits with 16A or 20A for NEC projects.

Any thoughts!

 

[RRaghunath]

MCBs are limited by their short circuit rating which is 10kA typically. In industrial distribution boards the SC rating even in final circuits is likely to be >10kA, thus excluding the use of MCB.
MCCBs come with protection modules with settable protections. So, use of MCCBs gives us better flexibility as regards to coordinating the protection upstream of the final circuit. This is unlike the MCB that comes with fixed protection curve.
With regard to protection of the cable or equipment in the final circuit also, I don't anticipate any issue.

 

[che12345]

Dear Mr. NickParker
" #1. ... a MCB and MCCB with 16A rating. MCB will trip based on the curve type, say if B curve is used, it trips between 3-5 times the 16A. Therefore, the instantaneous pickup would be anywhere between 48-80A."
YES, the instantaneous trip current is dependent on the Type B,C,D...
Attention: A MCB has (thermal and magnetic) trips. The thermal trip curve is comment and is independent of Type B,C,D .... It shall trip when > one time the current rating. The tripping time is dependent on the over-current level and whether on hot/cold curve.
"" #2. .... Since this is a project in IEC world, and my counterpart in Europe says always MCB to be used for the final circuit; his argument is that, for the final circuit as the fault current would be lower hence MCB would trip and for MCCB it would not, as the instantaneous pickup will be greater than the fault current.
NOT true. Both MCB and MCCB can have (thermal + magnetic) trips. For MCB, the trip current and Type B,C,D... are NOT adjustable. For MCCB, the rated current and the instantons trip currents are usually independently adjustable. A MCCB which is more costly and bigger in size are more versatile with two or more independent adjustable.
"...#3. We always used MCCB for the final circuits with 16A or 20A for NEC projects."
Both MCB or MCCB with thermal + magnetic trips are acceptable. MCBs are of lower cost and size. Attention either MCB or MCCB , the rated kA shall be > fault kA level at the point of application. Note: most MCB are <10kA, while most MCCB are >10kA.
Che Kuan Yau (Singapore)

 

[jraef]

In North America, you must use breakers that are listed as “Branch Protection” devices. Up until recently, that was always going to be an MCCB, because here, MCBs were only listed as “supplementary protectors” and required a Branch Protection listed device ahead of them anyway. So that explains why you would not have used MCBs here (“NEC land”) in the past. That has changed recently because some of the IEC style MCBs are now UL-489 listed as Branch Protection, but that is not yet widespread.

Those same rules don’t apply in IEC land.


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