MCB Vs ACCB

[NickParker]

When to use MCCB as incomer? and when to use ACB as Incomer? as both the ACBs and MCCBs are available in the range of 630A - 3200A (MCCBs in this range also has Icw rating)

In what applications ACBs are preferred over MCCB and Vice versa?

 

[Sazirul]

The advantage of Air Circuit Breaker (ACB):
1. ACB doesn’t have any oil inside for any operation. For this reason, there is no chance of a fire hazard caused by oil.
2. Duration of the arc is the same for all values of small and high currents interruptions.
3. Due to the duration of the arc is smaller that’s means less amount of heat realized from arc to current carrying contacts and for this reason, the service life of the contacts becomes longer.
4. The stability of the system can be well maintained by using ACB.
5. It requires less maintenance compared to any oil circuit breaker (OCB).

The advantage of Moulded Case Circuit Breaker (MCCB):
1. MCCBs are Compact in size. For this reason, it saves considerable space in panel design.
2. MCCBs has minimized downtime. Unlike in a fuse-based system, there's no searching for a replacement fuse. It can be Reset & Switched On again immediately after finding the fault that caused the tripping during operation.
3. MCCBs can clear several faults before it is due for replacement.
4. MCCBs are "Maintenance Free" and its recurring costs are less.
5. When MCCBs are used, then there is no possibility of single phasing due to fault in only one phase.
6. Some multi-purpose accessories can be fitted with the MCCB.

Source: Features of MCCB and ACB with Advantage



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[che12345]

Dear Mr NickParker

Q1. When to use MCCB as incomer? and when to use ACB as Incomer? as both the ACBs and MCCBs are available in the range of 630A - 3200A (MCCBs in this range also has Icw rating)
A1. The points answered by Mr Sazirul are correct and relevant.
A1.1 However, there is one very important point not covered is, as you had observed "(MCCBs in this range also has Icw rating)"
A1.1.1 [All] MCCB (1s) Icw ratings are [very very much lower] than its Icu rating
e.g. a) a 400A MCCB with Icu of 100kA is rated (1s) Icw of 5kA !
b) a 1600A MCCB with Icu of 100kA is rated (1s) Icw of 20kA !
c) a 3200A ACB with Icu=Ics of 100kA is rated (1s) Icw of 100kA or (3s) Icw of 75kA

Q2. In what applications ACBs are preferred over MCCB and Vice versa?
A2. For the incoming, ACB is preferred, in order to achieve better discrimination coordination with the outgoings; which are usually MCCBs.
A2.1 In most cases it is almost [impossible to achieve discrimination coordination] between incoming MCCB and out-going MCCBs; in the event of a fault with high short-circuit current.
A2.2 All MCCB manufacturers do provide a "selectivity" table between two MCCBs [either full or up to a certain] current level only, beyond which selectivity fails.
A2.3 In all cases, discrimination coordination can be achieved with incoming ACB and outgoing MCCBs. This is a very important requirement by [all] marine classification societies world wide.
Che Kuan Yau (Singapore)

 

[Sazirul]

Thank You, Mr. Che Kuan Yau for more depth explanation.

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