1. TOPIC : EARTH LEAKAGE CIRCUIT
BREAKER
(ELCB)
: MINIATURE CIRCUIT BREAKER
(MCB)
MADE BY: ID NO.
EN NO..
2. ABOUT ELCB:
•The earth leakage circuit breaker (ELCB)
is one such device which senses the
extremely small leakage currents and
thus prevents death , injury or fire arising
from the electric shocks . The device ,
also called a residual current circuit
breaker (RCCB) cut off the supply before
any real danger arises.
3. •The ELCB or the RCCB operate very
quickly with extremely small leakage
currents i.e. the time in which they
operate is far less as compared to that
of the fuse or the ( MCB). These
breakers are extensively used in the
residential , commercial and industrial
premises.
4. WORKING OF AN ELCB:
• The ELCB consists of an operating coil and a trim
mechanism which in turn trips the supply to the
circuit. It will operate if a live terminal or conductor
is touched by an earthed object or person provided
the leakage current exceeds the rated operating
current of the ELCB .
5. CONSTUCTION OF ELCB:
• The phase and neutral wires of the circuit being
protected , are led through one winding of a
transformer . A second winding contols the tripping
mechanism . Under normal condition , when there
is no leakage current the tripping mechanism is not
energized and the relay contacts are kept closed
using a spring mechanism .
6. • When the earth leakage occurs from either the
phase or the neutral side of the circuit , the currents
are unbalanced by an amount equal to the leakage
current and if this current reaches the rated tripping
current of the ELCB , the tripping mechanism will
operate opening he ELCB contacts .
• A test button is included in the ELCB for testing its
trip mechanism . This test should be carried out
periodically to ensure its satisfactory working . The
ELCB can be reset manually after its operation . But
it cannot be reset , as long as the leakage persists .
7. • The ELCB is provided near the main switch board to
protect the whole of the residence installation from
leakage in any circuit or appliances , by switching
off the supply .
8. MINIATURE CIRCUIT BREAKER
(MCB)
• The miniature circuit breaker is an electro –
mechanical device that operates and disconnect
the circuit when the current reaches a certain pre
determined value . The MCB is the most modern
substitute for a conventional rewirable fuse and
provides protection against overloads and short
circuits .
9. • The MCB operates at 125% of the rated currents ,
E.g. a 10 amp .MCB will operates at 11.5 amp as
compared to a rewirable fuse of the same rating
which will operates at 20 amp.
11. COMPONENTS OF MCB
1) SILVER GRAPHITE CONTACTS
2)ARC CHUTES & HORNS
3)MCB HOUSING
4)INNER MECHANISM
5)ANGULAR VENTS
6)SIMULTANEOUS TRIPPING OF
ALL PHASE IN MULTIPLE MCB’S
12. •1) Silver Graphite contacts:: While
breaking very high short circuit currents ,
the breaker contacts separate. These
contacts remain closed under normal
condition . If ordinary silver alloy contacts
are used , the contacts normally bounce ,
resulting in contact welding . For this
purpose silver – grafite is used for the
contacts since it is a non melting material.
13. • 2) Arc Chutes or Horns : :As the contacts separate ,
an arc is drawn between them . The arc is nothing
but a self sustained discharge of electricity that is
produced when the contacts separates .
• Under normal condition , since the currents carried
by the contacts is less , the stength of the magnetic
field produced is also less . However during short-
circuit or over loads , since the current in the circuit
increases , the strength of the magnetic field
produced also increases .
14. • 3) MCB Housing :: The body of the MCB is made of
plastic material having high melting point , high
dielectric strength and minimum water absorption.
• 4) Inner Mechanism :: The moving contacts of the
MCB are closed in a sheet metal casing and not
inside plastic . This is because plastic will tend to
charge its shape and accuracy under continuous
stresses of load and consistent tripping .
15. • 5) Angular vents :: are provided to provided to
prevent the dust from entering into the casing . Thus
dust free perfect electrical contacts are obtained .
• 6)Simultaneous tripping of all phases in multiple
MCB’s:: The tripping design is so done that in case
of any over load or short circuit in one phase , all
the phases trip simultaneously . Thus , the damage
done due to single phasing is reduced .
16. WORKING OF MCB
• There are two main operation of the MCB .
• (1) The first operation is thermal , resulting in the
inverse time current characteristics . This operation is
obtained with the help of the bimetallic strip . Here , as
the current flowing through the bi-mettalic strip increases
during overloads , it deflects or bends and in the process
causes the fixed and moving contacts to separate . The
inverse time current characteristics mean , higher the
current , smaller will be the time in which the MCB
operates and vise-versa .
17. •(2) During short circuits , as the current
rises to very high levels very rapidly ,
the rising current energizes the
solenoid . This in turn operates the
plunger to strike the trip level . This
causes the fixed and moving contacts
to separate .
18. • Thus an MCB instantly switches off the supply
automatically , when there is a short circuit or an
overloads .In this way , damage to the equipments and
wiring is prevented .
• The supply is re-started after tripping by simply
switching on the MCB switch . The MCB does not show
wear and tear with time . It does not require any
maintenance or repairs.
19. • MCB’s are used in residences , offices , shops , in the
complete wiring of building etc. Though they are
expensive as compared to fuses , there is no cost
involved in resetting them after operation . We simply
have to switch on the MCB . In case of the fuse , it will
have to be re-wired once it has blown out . MCB’s are
being used extensively these days and have virtually
replaced the re- wirable fuses .
