3. • It is the Simplest • ‘Miniature • ‘Moulded Case • ‘Earth Leakage
Form of Circuit Breaker’ Circuit Breaker’ Circuit-Breaker’
Protection (MCB). (MCCB). (ELCB).
Against Excess • It is a • It Provides Over • It is Current
Current, Short Electromagnetic Load and Short Operated
Circuit and Earth Device which Circuit Device Designed
Fault. Operates and Protection to to operate when
• A Fuse is a Wire Disconnects the Normal Service a leakage
of Short Length Circuit Reaches apart from Current Exceeds
having Low - a Pre- Serving as a Pre-
Melting Point. Determined ‘Circuit - Determined
Value. Breaker’. Value.
4. INTRODUCTION
• An MCB is an Electromagnetic Device which Operates and Disconnects the
Circuit when the Current reaches a pre determined value. The MCB may ,
therefore, be used in lieu of fuse & can be fitted in consumer’s distribution
panel.
• It is most modern substitute for conventional rewireable fuse with most
accurate & efficient system in over-load & short circuit protection. In fact, it
provides over-load protection & short circuits protection whereas FUSE offers
short circuit protection only.
• An MCB will normally operate at 1.25 times it rated current i.e. 20 A. MCB
operates at 25 A compared with 30 A for cartridge fuse or 40 A for rewireable
type of fuse of the same rating. Some manufactures have invented most
efficient MCB which operates at 1.05 times the full load current.
• Other advantages of MCB are that they can be quickly reset by hand after
operations without any cost and they cannot be re-closed if the fault still exists.
They can be manually re-closed after rectifying the fault.
• Also the MCB which has tripped due to over-load or short circuit can be readily
identified as the dolly or toggle or operating knob automatically moves to the
“OFF” position.
7. E INTRODUCTION
L • An Earth Leakage Circuit Breaker is a safety device used in
electrical installations with high earth impedance to prevent
Shock.
C
• Many electrical installations have a relatively high earth
impedance.
These may be due to use of local earth rod to dry ground
conditions.
B
• These installations have a major problem if no ELCB is used.
During live to earth fault current,two conditions occur. Because
earth impedance is high,
1. Not enough current exist to trip a fuse or circuit breaker, so
condition persists uncleared indefinitely .
2. The high impedance earth can not keep the voltage of all
exposed CPC connected metalwork to safe voltage all such
metalwork may rise to close to live conductor voltage.
TYPES OF ELCB:
I. Voltage Operated:- They Provide a major advance in safety
for mains electrical supplies with inadequate earth impedance.
II. Current Operated:- They Provide protection against earth
leakage, through the details & method of operation are
different.
