Circuit breakers are devices designed to automatically open an electrical circuit under abnormal current conditions without being damaged. They can be reset to resume normal operation, unlike fuses which must be replaced. There are different types of circuit breakers including oil, air, SF6, and vacuum. Circuit breakers can sense overcurrent through either thermal or magnetic methods and operate on either a time delay or instantaneous basis. Common circuit breakers used in buildings include miniature circuit breakers and molded case circuit breakers.

2. Circuit Breakers
Device designed to
open the circuit
automatically under
abnormal conditions
without damage to
itself when properly
applied within its
rating.

3. Basic Difference Between Fuse &
Circuit Breaker
Fuse
• Design to open the
circuit when current
exceed the desire limit.
• If fuse is blow then it
has to be replace.

4. Circuit Breaker
• Not directly design to open the
circuit like Fuse or Breaker
• Its opening depend upon
magnitude and time of Overload
current
• Circuit breaker can be reset
(either manually or automatically)
to resume normal operation.
Basic Difference Between Fuse &
Circuit Breaker

5. Types of Circuit Breakers
• Oil circuit breaker
• Air circuit breaker
• SF6 circuit breaker
• Vacuum circuit breaker

6. Self-Actuated Circuit Breaker
Two methods circuit breakers sense circuit current:
Thermal
• Sense circuit current through
the production of heat
• Generally uses some type of
heating element in series with
the load
• The heater is located close to
a bimetallic strip
• The bimetallic strip is
mechanically connected to
the moveable contacts
• There is a time delay before
the circuit opens
• The time delay depends on
the amount of over current
Magnetic
• It also known as Instantaneous trip
circuit breaker
• Senses circuit current by connecting
a coil in series with the load
• When current flows thought the
circuit, a magnetic field is
established around the coil
• The magnetic field attracts the
metal arm of a solenoid
• When the magnetic field becomes
intense enough the metal arm
mechanically opens the contacts
• There is very little time delay in
opening the contacts when an
abnormal condition occurs

7. Thermal Circuit Breaker
Symbol Schematic Diagram

8. Overheated Circuit Breaker
(Thermal Type)

9. Thermal Breaker

10. Magnetic circuit breaker

11. Magnetic Circuit Breaker
Symbol Schematic Diagram

12. Thermo-magnetic circuit breaker
• Employs both thermal and magnetic current
sensors
• More efficient and disconnect within
millisecond

13. Classification and Types of Low
Voltage Circuit Breaker
• Miniature circuit breakers
• Molded case circuit breakers

14. Miniature Circuit Breaker (MCB)
• Normally work with currents below 100 amperes.
• They are the type of low voltage circuit breaker that is
typically found in the fuse box of a residential or commercial
building.
• Miniature circuit breakers are designed to be installed in a
shared fuse box, from which several electric circuits are
protected.
• The current ratings of a miniature circuit breaker normally
have fixed values that are established during production and
can’t me modified by the user

15. Miniature Circuit Breaker (MCB)

16. Single Poles MCB
A Single-Pole low voltage circuit breaker only occupies one
space in a fuse box. Single-pole circuit breakers are typically
used for electric circuits with low power requirements that
only use one live conductor, such as those providing power for
lamps or general purpose electric outlets.

17. Double-pole MCB
A Double-Pole low voltage circuit breaker occupies two
spaces in a fuse box, and is used for devices that operate with
two live conductors, such as most residential Air Conditioner
models. When a double-pole circuit breaker is tripped, both
lines are disconnected even if only one of them was involved
in the electrical fault.

18. Triple-pole MCB
A Triple-Pole low voltage circuit breaker occupies three
spaces in a fuse box and is used to protect electric equipment
that works with three-phase power. The electric motors of
elevators and large central Air Conditioning units typically
work with three-phase power and are protected with triple-
pole low voltage circuit breakers.

19. • Higher current ratings when compared
to miniature circuit breakers.
• But due to their size they can’t be
installed in a traditional fuse box.
Instead.
• Molded case circuit breakers are
typically installed in individual metallic
boxes or in industrial switchboards
which have larger slots to accommodate
them.
• Some fuse boxes that are designed for
miniature circuit breakers may include
one slot for a molded case circuit
breaker that is used as the main breaker
Molded Case Circuit Breaker (MCCB)

20. Overheated Circuit breaker Application
• Overload Heater
• Its basically used to
protect motor from
overheating
• Its Thermal model
of heating and
cooling is match with
model of Model

21. Earth Leakage Circuit Breaker (ELCB)
An earth leakage circuit breaker (ELCB) is a safety device used in electrical
installations with high earth impedance to prevent shock. It detects small stray
voltages on the metal enclosures of electrical equipment, and interrupts the circuit
if a dangerous voltage is detected. Once widely used, more recent installations
instead use residual current circuit breakers which instead detect leakage current
directly.

22. Earth Leakage Circuit Breaker (ELCB)

23. Residual Current Circuit Breaker (RCCB)
• Its trip when sense earth fault
current
• Check the phase (line) current
and neutral (return) current
• Trip if fault remain up to
30mSec
• Its extremely effective in shock
protection
• 30mA and 100mA tripping are
widely use

24. Difference between ELCB and RCCB
ELCB
• It is old technology
• It is connected to
Phase, Neutral as
well as earth line
• It is not
recommended over
RCCB
RCCB
• Its New technology
•It is connected to
only Phase and
Neutral line
•It is also known as
Current-operated
ELCB
Their working principle is same but their
operation and connectivity and different

25. Thank you