MCBs or Miniature Circuit Breakers are
electromechanical devices providing a resettable protection against two types
of overcurrent situations: Overload and Short Circuit.
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 operated and thus offers improved
operational safety and greater convenience without incurring large operating
cost.
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| Miniature Circuit Breaker |
ENTEK MCBs are of following types
1
Single
Pole
2
1 Pole
(with N)
3
2 Pole
(DP)
4
3 Pole
(TP)
5
3 Pole with N (TPN)
There are two arrangement of operation of miniature circuit breaker.
One due to thermal effect of over electric current and other due to
electromagnetic effect of over current. The thermal operation of miniature
circuit breaker is achieved with a bimetallic strip.
Whenever continuous over electric current flows through MCB, the
bimetallic strip is heated and deflects by bending. This deflection of
bimetallic strip releases mechanical latch. As this mechanical latch is attached
with operating mechanism, it causes to open the miniature circuit
breaker contacts.
But during short circuit condition, sudden rising
of electric current, causes electro-mechanical displacement of plunger
associated with tripping coil or solenoid of MCB. The plunger strikes the
trip lever causing immediate release of latch mechanism consequently open the
circuit breaker contacts. This was a simple explanation of miniature
circuit breaker working principle.
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| MCB Characteristics |
ENTEK MCB Characteristic Curves
Type B characteristic curves.
Type C characteristic curves.
The classification of Type B, C is based on fault current rating at
which magnetic operation occurs to provide short time protection (typically
less than 100ms) against short circuits. It is important that equipment having
high inrush currents should not cause the circuit-breaker to trip
unnecessarily, and yet the device should trip in the event of a short-circuit
current that could damage the circuit cables.
Type B devices are generally suitable for domestic applications. They may
also be used in light commercial applications where switching surges are low or
non-existent. Type B devices are designed to trip at fault currents of 3-5
tomes rated current. For example a 10A device will trip at 30-50A.
Type C devices are the normal choice for commercial and industrial
applications. Type C devices are designed to trip at 5-10 times In (50-100A for
a 10A device).
