Full form of MCCB – The full form of MCCB is Molded Case Circuit Breaker.

What is MCCB – Definition of MCCB is given below –

Definition –

MCCB is a switching device which is used in LT electrical system. It provides protection against overload & short circuit. Fault sensing arrangements are installed inside MCCB & shunt release is provided for remote tripping of MCCB. It is available between 100A & 630Acurrent.

Working Principle of MCCB / Function of MCCB –

It provides protection against overload & short circuit for which each MCCB has two different mechanisms. Working of each protection is given below –

1. It provides protection against overload through thermal mechanism. It has bimetallic contacts which expand & contract on temperature changes. Under normal condition these contacts allow normal current to flow but when current exceeds its trip limit, the bimetallic contacts start heating up & expand until the circuit is isolated/tripped. When MCCB is tripped, faulty circuit is isolated from circuit & the temperature of bimetallic contacts starts getting normal & MCCB again is ready for next operation.

2. Protection against short circuit – if current is very high, fault current should be interrupted immediately. This is achieved by electromagnetic induction. Whenever fault occurs, the high current induces a magnetic field in a solenoid coil located inside the breaker, this magnetic induction trips a contact & current is interrupted. In the tripping process, arc is produced & that is dissipated by taking suitable measures inside the breaker. These breakers can be manually switched off or on also which is required during maintenance or other purpose.

MCCBs are available with protection range from 50% to 100% of rated MCCB.

Ex –200A, TP MCCB can be used from 100A load to 200A in steps of 10% e.g. 110A, 120A, 130A, 140A, 150A, 160A, 170A, 180A, 190A & 200A. On every stage MCCB will provide overload & short circuit protection.

Selection of MCCB rating –

Following criteria should be followed while selecting a MCCB –

• It should be capable to carry the rated current of load, (Note: Rating of MCCB should not be much higher than rated/full load current otherwise MCCB will not trip on fault).
• Check number of poles – TP, TPN & 4P where

TP (for 3 phase load) = TP stands for Triple pole which means three phases (R,Y,B) & these phases will be part of MCCB & neutral is not required for load. These 3 phases are opened & closed with the operation of MCCB.

TPN (for 3-phase load) = TPN stands for Triple pole with neutral where three phases will be part of MCCB & will be closed or opened with the operation of MCCB but neutral will be connected directly with load & neutral will remain connected with load ,

4P (for 3-phase load) = 4P means Fore pole which means 3 phases & a neutral and all will be part of MCCB. In this case, 3-phases &neutral will be part of MCCB &opened & closed with MCCB operation.

• Type of protection–According to Time Curve protection.
• Fault current rating which should be in kA (thousand amperes) which means that a MCCB can withstand the fault current of short circuit,
• Operating Handle – with or without handle

Ex – 200A TP MCCB with 35kA fault current& operating handle.

CURRENT RATING OF MCCBs –

A typical range of Three phase MCCB –  100A, 125A, 150A, 200A, 250A, 315A, 400A, 630A,

(Note: MCCBs are available with 25-50KA fault level.)

Frequently Asked Questions (FAQs) on MCCB –

Q1) What is the difference between MCB & MCCB?

Ans) Full form of MCB is Miniature Circuit Breaker while MCCB stands for Molded Case Circuit Breaker. Function of both MCB & MCCB are same i.e a) work as switching device b) to protect equipment from overloading & short circuit. Only difference in both is current rating. MCB is used for small current rating loads while MCCBs are used for higher current rating loads.

MCBs are available from 2A – 63A while MCCBs are available from 63A – 800A.

Q2) MCCB is used in motor for which protection?

Ans) MCCB/MCB (depending on current rating) is used in the starter. It provides back-up protection for motor from overloading & short circuit. Primary protection of overloading of motor is provided by the OLR (over load relay) in the starter.

Detail of starter & OLR protection is provided separately in different sections.

Q3) How ELCB (Earth Leakage Circuit Breaker) differs from MCCB.

Ans) The main difference between ELCB & MCCB is – ELCB provide protection against earth fault in electrical equipment while MCCB provides protection against overloading & short circuit in equipment & electrical system.

ELCB – To know more about it, click on ELCB

MCCB – Detail of MCCB is given in above sections.

Q4) What is the use of shunt trip coil in MCCB?

Ans) Shunt trip in MCCB is an optional tripping device which trips MCCB mechanically through some external command/source. External command/source may be manual (remote tripping of MCCB) or automatically (via interconnecting with some other equipment/system). Shunt trip is not integral part of MCCB but can buy it separately whenever it is required for system.

Q5) What is MCCB panel?

Ans) MCCB panel is an electrical distribution panel which is used for distribution of electrical supply to different loads. Each MCCB of this panel works as a switching point to a particular load for which it is installed. This MCCB panel is installed in a facility at a suitable location so that operator can operate it without any problem.

Q6) Why MCCB need to put off after trip?

Ans) MCBB need to put off after trip because it is designed in such a way that operator must understand that MCCB has tripped on fault & corrective action is required to clear the fault. If This feature is not there in MCCB then it will be difficult for the operator to know that MCCB has bee tripped on fault or some one has switched off intentionally.