Molded Case Circuit Breakers
Molded Case
Circuit Breakers are electromechanical devices which protect a circuit from Over-current and Short Circuit. It provides Short Circuit Protection and also Over-current
and for circuits ranging from 63 Amps up to 3000 Amps.
Their primary
functions are to provide a means to manually and automatically open a circuit under
overload or short circuit conditions. The over-current, in an electrical
circuit, may result from short circuit, overload or faulty design.
MCCB is an
alternative to a fuse since it does not require replacement once an overload is
detected. Unlike fuse, an MCCB can be easily reset after a fault and offers
improved operational safety and convenience without incurring operating cost.
Molded case
circuit breakers generally have a Thermal
element for over-current and Magnetic element for short circuit release which
has to operate faster.
MCCBs are
manufactured such that end user will not have access to internal workings of
the over-current protection device. Generally constructed of two pieces of
heavy-duty electrically insulated plastic, these two halves are riveted
together to form the whole. Inside the plastic shell is a series of thermal
elements and a Spring-loaded trigger.
When the thermal
element gets too warm, from an over-current situation, the spring trips, which
in turn will shut off the electrical circuit.
Types of MCCBs
Larger molded
case circuit breakers have adjustable range setting on the face of the device. Molded
case circuit breakers can range in size from 32 Amperes up to 3000 Amperes.
Molded Case
Circuit Breakers have the following Specifications
- Current Rating - Amperes
- Current Setting Range - Amperes
- Short Circuit Rating - Kilo Amperes (KA)
- Operating Characteristics - Normal / Current Limiting Type
MCCBs are now
available with a variety of Releases or Operating Mechanisms these are given
below
- Thermal Magnetic Release
- Electronic Release
- Microprocessor Release
- Thermal Magnetic Release MCCB
Thermal-magnetic
circuit breakers use bimetals and electromagnetic assemblies to provide over-current
protection. Their characteristic inverse time tripping under overload
conditions is ideally suited for many applications varying from residential to
heavy industrial loads. For higher level (short circuit) over currents,
instantaneous trip characteristics allow molded case circuit breakers to
interrupt with no intentional delay.
The adjustable
overload protection is from 70% to 100% of the nominal current and short
circuit setting from 5 to 10 times of the rated current is possible.
The minor disadvantage
of the release is that operating characteristics of the breaker may vary
depending on the ambient temperature.
Electronic
Release MCCB
Electronic or
Static Release Molded Case circuit breakers use power electronic circuitry to
provide over-current protection. The Continuous adjustable overload protection
from 60% to 100% of the nominal current and short circuit setting from 2 to 10
times of the rated current is possible.
The advantage of
the release is that operating characteristics of the breaker is independent of
the ambient temperature.
This wide
flexibility takes care of future increases in load capacity of an installation
and ensures better planning at an optimum cost.
Microprocessor
release MCCB
Microprocessor
release Molded Case circuit breakers use microprocessors to provide over-current
protection. The Microprocessor release works on monitoring of current True
R.M.S value. It is simulated and calculated from peak values, which installed
microprocessor, can detect.
There is high
Flexibility through multiple adjustments of protection settings, High repeat
accuracy and High reliability.
Time delays can
be provided for Short Circuit Release better discrimination and co-ordination
using LCD display. System Diagnosis is possible as it stores the Trip history
within the internal memory. Trip current indication is also available for
understanding of type of fault and set-up programming at site.
