Exp. 2 - Study of Miniature Circuit Breakers (MCB) and
Earth leakage Circuit Breakers (ELCB)
Surabhi Raman
17BEE0029
Aim:
Study the applications, types and characteristics of various types of MCBs and ELCBs
MCBs or Miniature Circuit Breakers are electromechanical devices which protect an electric circuit
from an overcurrent. The overcurrent, in an electrical circuit, may result from short circuit, overload
or faulty design.
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.
MCBs are popularly used for load break, protection and isolation of a sub-circuit including motor
sub-circuits, lighting circuits and control circuits. The main usage area of MCBs is low voltage (LV)
side, i.e., mainly in domestic, light-industrial or commercial applications.
These are manufactured in 1, 2, 3 & 4 pole versions of different current and voltage ratings. Similar
to the HRC fuses, these are used for performing two major functions such as over current protection
and short-circuit protection.
Miniature Circuit Breakers are used to protect lower current circuits and have the following
specifications
Current rating - Amperes
Short Circuit Rating - Kilo Amperes (kA)
Operating Characteristics - B, C or D Curves
Miniature Circuit Breakers are usually available in the range of 0.5A to 100A. An MCB's short circuit
rating is given in kiloamps (kA), and this indicates the level of its ability to work. For example a
domestic MCB would normally have a 6kA fault level, whereas those used in an industrial
application may need a unit with a 10kA fault capability.
Working Principle of MCB
The operation of the MCB includes two stages, i.e., thermal operation and short circuit operation.
The former operation based on the thermal effect of over current while the later operation is based
on the electromagnetic effect of over current.
