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1. MCB and MCCB
PREPARED BY
MD. MAMUNOOR ISLAM

2. Miniature Circuit Breaker (MCB)
✓ Miniature Circuit Breakers are electromechanical devices which protect an
electrical circuit from an overcurrent.
✓ The overcurrent, in an electrical circuit, may result from short circuit, overload or
faulty design.
✓ An MCB is a better alternative to a Fuse since it does not require replacement once
an overload is detected.
✓ Unlike fuse, an MCB can be easily reset and thus offers improved operational
safety and greater convenience without incurring large operating cost.

3. Miniature Circuit Breaker (MCB)
✓ MCB is a switch which automatically turns off when the current flowing through it
passes the maximum allowable limit.
✓ Generally MCB are designed to protect against over current and over
temperature faults (over heating).

4. Miniature Circuit Breaker (MCB)

5. The working principle of MCB
✓There are two main types of trip mechanism.
➢ A bi-metal provides protection against overload current.
➢ An electromagnet provides protection against short-circuit current.

6. The working principle of MCB
✓ Whenever continuous overcurrent flows through MCB, the
bimetallic strip is heated and deflects by bending.
✓ This deflection of bimetallic strip releases a mechanical latch.
✓ As this mechanical latch is attached with the operating mechanism, it
causes to open the miniature circuit breaker contacts, and the MCB
turns off thereby stopping the current to flow in the circuit. T
✓ o restart the flow of current the MCB must be manually turned ON.
✓ This mechanism protects from the faults arising due to overcurrent or
overload.

7. The working principle of MCB
✓ During short circuit condition, the current rises suddenly, causing
electromechanical displacement of plunger associated with a tripping
coil or solenoid.
✓ The plunger strikes the trip lever causing immediate release of latch
mechanism consequently open the circuit breaker contacts.

8. Arc Chutes
✓ In an MCB, arc chutes or arc dividers are used for
arc quenching.
✓ When the contacts of an MCB separate,
generating an electrical arc between them
through air, the arc is moved into the arch chute
where it is divided into small segments.
✓ The overall energy level of the arc gets split up
which is not sufficient to sustain the arc and
therefore it gets dissipated.

9. Current Ratings of MCB
✓Standard rating of MCB is 1A, 2A, 3A, 4A, 6A, 10A, 13A,
16A, 20A, 25A, 32A, 40A, 50A, 63A, 100A for MCB.

10. Moulded Case Circuit Breaker (MCCB)
➢Moulded Case Circuit Breakers are electromechanical devices which
protect a circuit from Overcurrent and Short Circuit.
➢They provide Overcurrent and Short Circuit Protection for circuits
ranging from 63 Amps up to 3000 Amps.

11. MCB Vs. MCCB
•MCB stands for “Miniature Circuit Breaker”.
•Rated current under 100 amps.
•Interrupting rating of under 18,000 amps
•trip characteristics may not be adjusted
•Suitable for low current circuits (low energy requirement), i.e. home wiring.
•Generally, used where normal current is less than 100 Amps.

12. MCB Vs. MCCB
▪ MCCB stands for “Molded Case Circuit Breaker”.
▪ Rated current in the range of 10-2500 amps.
▪ Thermal operated for overload and & Magnetic operation for instant trip in SC
(Short circuit conditions)
▪ Interrupting rating can be around 10k – 200k amps.
▪ Suitable for high power rating and high energy i.e. commercial and industrial use.
▪ Generally, used where normal current is more than 100 Amps.

13. Types of CB
Single Pole (SP) MCB: A single pole MCB provides switching and protection for one single phase
of a circuit.
Used: for Single Phase circuit
Double Pole (DP) MCB: A two Pole MCB provides switching and protection both for a phase and the
neutral.
Used: for Single Phase circuit
Triple Pole (TP) MCB: A triple/three phase MCB provides switching and protection only to three
phases of the circuit and not to the neutral.
Used: for Three Phase circuit.

14. Types of CB
3 Pole with Neutral (TPN (3P+N) MCB):
A TPN MCB, has switching and protection to all three phases of circuit and additionally
Neutral is also part of the MCB as a separate pole. However, Neutral pole is without any
protection and can only be switched.
Used: for Three Phase circuit with Neutral