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intelligent
MCB
Miniature Circuit Breaker or MCB
HRC FuseMiniature Circuit BreakerELCB and RCCB
What is MCB?
Nowadays we use more commonly miniature ment of plunger associated with tripping coil
circuit breaker or MCB in low voltage electrical or solenoid of MCB. The plunger strikes the trip
network instead of fuse. The MCB has some ad- lever causing immediate release of latch mecha-
vantages compared to fuse. nism consequently open the circuit breaker con-
/ƚ ĂƵƚŽŵĂƟĐĂůůLJ ƐǁŝƚĐŚĞƐ Žī ƚŚĞ ĞůĞĐƚƌŝĐĂů ĐŝƌĐƵŝƚ ƚĂĐƚƐ͘ dŚŝƐ ǁĂƐ Ă ƐŝŵƉůĞ ĞdžƉůĂŶĂƟŽŶ ŽĨ ŵŝŶŝĂƚƵƌĞ
ĚƵƌŝŶŐ ĂďŶŽƌŵĂů ĐŽŶĚŝƟŽŶ ŽĨ ƚŚĞ ŶĞƚǁŽƌŬ ŵĞĂŶƐ circuit breaker working principle.
ŝŶ ŽǀĞƌ ůŽĂĚ ĐŽŶĚŝƟŽŶ ĂƐ ǁĞůů ĂƐ ĨĂƵůƚLJ ĐŽŶĚŝƟŽŶ͘ DŝŶŝĂƚƵƌĞ ŝƌĐƵŝƚ ƌĞĂŬĞƌ ŽŶƐƚƌƵĐƟŽŶ
The fuse does not sense but miniature circuit DŝŶŝĂƚƵƌĞ ĐŝƌĐƵŝƚ ďƌĞĂŬĞƌ ĐŽŶƐƚƌƵĐƟŽŶ ŝƐ ǀĞƌLJ
breaker does it in more reliable way. MCB is simple, robust and maintenance free. Gener-
ŵƵĐŚ ŵŽƌĞ ƐĞŶƐŝƟǀĞ ƚŽ ŽǀĞƌ ĐƵƌƌĞŶƚ ƚŚĂŶ ĨƵƐĞ͘ ally a MCB is not repaired or maintained, it just
ŶŽƚŚĞƌ ĂĚǀĂŶƚĂŐĞ ŝƐ͕ ĂƐ ƚŚĞ ƐǁŝƚĐŚ ŽƉĞƌĂƟŶŐ replaced by new one when required. A miniature
ŬŶŽď ĐŽŵĞƐ Ăƚ ŝƚƐ Žī ƉŽƐŝƟŽŶ ĚƵƌŝŶŐ ƚƌŝƉƉŝŶŐ͕ ƚŚĞ circuit breaker has normally three main construc-
faulty zone of the electrical circuit can easily be ƟŽŶĂů ƉĂƌƚƐ͘ dŚĞƐĞ ĂƌĞ͗
ŝĚĞŶƟĮĞĚ͘ Ƶƚ ŝŶ ĐĂƐĞ ŽĨ ĨƵƐĞ͕ ĨƵƐĞ ǁŝƌĞ ƐŚŽƵůĚ Frame of Miniature Circuit Breaker
be checked by opening fuse grip or cutout from The frame of miniature circuit breaker is a
ĨƵƐĞ ďĂƐĞ͕ ĨŽƌ ĐŽŶĮƌŵŝŶŐ ƚŚĞ ďůŽǁ ŽĨ ĨƵƐĞ ǁŝƌĞ͘ molded case. This is a rigid, strong, insulated
ϭ͘ YƵŝĐŬ ƌĞƐƚŽƌĂƟŽŶ ŽĨ ƐƵƉƉůLJ ĐĂŶŶŽƚ ďĞ housing in which the other components are
possible in case of fuse as because fuses have to mounted.
be rewritable or replaced for restoring the sup- KƉĞƌĂƟŶŐ DĞĐŚĂŶŝƐŵ ŽĨ DŝŶŝĂƚƵƌĞ ŝƌĐƵŝƚ
ƉůLJ͘ Ƶƚ ŝŶ ƚŚĞ ĐĂƐĞ ŽĨ D ͕ ƋƵŝĐŬ ƌĞƐƚŽƌĂƟŽŶ ŝƐ Breaker
ƉŽƐƐŝďůĞ ďLJ ũƵƐƚ ƐǁŝƚĐŚŝŶŐ ŽŶ ŽƉĞƌĂƟŽŶ͘ dŚĞ ŽƉĞƌĂƟŶŐ ŵĞĐŚĂŶŝƐŵ ŽĨ ŵŝŶŝĂƚƵƌĞ ĐŝƌĐƵŝƚ
2. Handling MCB is more electrically safe breaker provides the means of manual open-
than fuse. Because of to many advantages of ŝŶŐ ĂŶĚ ĐůŽƐŝŶŐ ŽƉĞƌĂƟŽŶ ŽĨ ŵŝŶŝĂƚƵƌĞ ĐŝƌĐƵŝƚ
MCB over fuse units, in modern low voltage elec- ďƌĞĂŬĞƌ͘ /ƚ ŚĂƐ ƚŚƌĞĞͲƉŽƐŝƟŽŶƐ ͞KE͕͟ ͞K&&͕͟ ĂŶĚ
trical network, miniature circuit breaker is mostly ͞dZ/WW ͘͟ dŚĞ ĞdžƚĞƌŶĂů ƐǁŝƚĐŚŝŶŐ ůĂƚĐŚ ĐĂŶ ďĞ ŝŶ
used instead of backdated fuse unit. ƚŚĞ ͞dZ/WW ͟ ƉŽƐŝƟŽŶ͕ ŝĨ ƚŚĞ D ŝƐ ƚƌŝƉƉĞĚ ĚƵĞ
1.3. Only one disadvantage of MCB over fuse ƚŽ ŽǀĞƌͲĐƵƌƌĞŶƚ͘ tŚĞŶ ŵĂŶƵĂůůLJ ƐǁŝƚĐŚ Žī ƚŚĞ
is that this system is more costly than fuse unit D ͕ ƚŚĞ ƐǁŝƚĐŚŝŶŐ ůĂƚĐŚ ǁŝůů ďĞ ŝŶ ͞K&&͟ ƉŽƐŝ-
system. ƟŽŶ͘ /Ŷ ĐůŽƐĞ ĐŽŶĚŝƟŽŶ ŽĨ D ͕ ƚŚĞ ƐǁŝƚĐŚ ŝƐ ƉŽƐŝ-
tŽƌŬŝŶŐ WƌŝŶĐŝƉůĞ DŝŶŝĂƚƵƌĞ ŝƌĐƵŝƚ ƌĞĂŬĞƌ ƟŽŶĞĚ Ăƚ ͞KE͘͟ LJ ŽďƐĞƌǀŝŶŐ ƚŚĞ ƉŽƐŝƟŽŶƐ ŽĨ ƚŚĞ
dŚĞƌĞ ĂƌĞ ƚǁŽ ĂƌƌĂŶŐĞŵĞŶƚ ŽĨ ŽƉĞƌĂƟŽŶ ŽĨ ƐǁŝƚĐŚŝŶŐ ůĂƚĐŚ ŽŶĞ ĐĂŶ ĚĞƚĞƌŵŝŶĞ ƚŚĞ ĐŽŶĚŝƟŽŶ
miniature circuit breaker. One due to thermal of MCB whether it is closed, tripped or manually
ĞīĞĐƚ ŽĨ ŽǀĞƌ ĐƵƌƌĞŶƚ ĂŶĚ ŽƚŚĞƌ ĚƵĞ ƚŽ ĞůĞĐƚƌŽ- ƐǁŝƚĐŚĞĚ Žī͘
ŵĂŐŶĞƟĐ ĞīĞĐƚ ŽĨ ŽǀĞƌ ĐƵƌƌĞŶƚ͘ dŚĞ ƚŚĞƌŵĂů Trip Unit of Miniature Circuit Breaker
ŽƉĞƌĂƟŽŶ ŽĨ ŵŝŶŝĂƚƵƌĞ ĐŝƌĐƵŝƚ ďƌĞĂŬĞƌ ŝƐ ĂĐŚŝĞǀĞĚ The trip unit is the main part, responsible for
ǁŝƚŚ Ă ďŝŵĞƚĂůůŝĐ ƐƚƌŝƉ ǁŚĞŶĞǀĞƌ ĐŽŶƟŶƵŽƵƐ ŽǀĞƌ proper working of miniature circuit breaker. Two
ĐƵƌƌĞŶƚ ŇŽǁƐ ƚŚƌŽƵŐŚ D ͖ ƚŚĞ ďŝŵĞƚĂůůŝĐ ƐƚƌŝƉ ŝƐ main types of trip mechanism are provided in
ŚĞĂƚĞĚ ĂŶĚ ĚĞŇĞĐƚƐ ďLJ ďĞŶĚŝŶŐ͘ dŚŝƐ ĚĞŇĞĐƟŽŶ D ͘ ďŝŵĞƚĂů ƉƌŽǀŝĚĞƐ ƉƌŽƚĞĐƟŽŶ ĂŐĂŝŶƐƚ ŽǀĞƌ
of bimetallic strip releases mechanical latch. As load current and an electromagnet provides pro-
ƚŚŝƐ ŵĞĐŚĂŶŝĐĂů ůĂƚĐŚ ŝƐ ĂƩĂĐŚĞĚ ǁŝƚŚ ŽƉĞƌĂƟŶŐ ƚĞĐƟŽŶ ĂŐĂŝŶƐƚ ƐŚŽƌƚͲĐŝƌĐƵŝƚ ĐƵƌƌĞŶƚ͘
mechanism, it causes to open the miniature cir- KƉĞƌĂƟŽŶ ŽĨ DŝŶŝĂƚƵƌĞ ŝƌĐƵŝƚ ƌĞĂŬĞƌ
cuit breaker contacts. There are three mechanisms provided in a single
Ƶƚ ĚƵƌŝŶŐ ƐŚŽƌƚ ĐŝƌĐƵŝƚ ĐŽŶĚŝƟŽŶ͕ ƐƵĚĚĞŶ ƌŝƐŝŶŐ ŵŝŶŝĂƚƵƌĞ ĐŝƌĐƵŝƚ ďƌĞĂŬĞƌ ƚŽ ŵĂŬĞ ŝƚ ƐǁŝƚĐŚĞĚ Žī͘
of current, causes electromechanical displace- If we carefully observe the picture beside, we will
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