Moulded Case Circuit Breakers (MCCB)
Moulded Case Circuit Breakers are electromechanical devices, which designed to provide circuit protection for low voltage distribution systems. They will protect connected devices against both overloads and short circuits.
They are most-commonly-used in panelboards and switchboards where they are fixed mounted, though some of the larger MCCBs available may be available in a drawout mount design. The selection of MCCB and contactor should be according to type 2 co-ordination for electrical starters.
MCCBs are available with special features which make them suitable for the protection of motor circuits when used in conjunction with a separate overload protection device. When used in such applications, they are often referred to as motor circuit protectors (MCPs).
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.
- Depending upon the application and required protection, an MCCB will use one or a combination of different trip elements that protect against the following conditions:
- Thermal overloads
- Short circuits
- Ground faults
- MCCBs are available with a variety of Releases or Operating Mechanisms these are given below
1) Thermal Magnetic Release : Thermal magnetic breakers can be affected by large differences in the ambient temperature. At ambient temperatures below 40°C, the breaker will carry more current than its continuous current rating.
The mechanical operation of the breaker carries more current than its continuous current rating. The mechanical operation of the breaker could be affected if the temperature is significantly below the 40°C standard.
The breakers will carry less current than their continuous rating if the temperature is above 40°C, and could cause nuisance tripping. It could also cause unacceptable temperature conditions at the terminals of the breaker.
2) Electronic Release : Electronic trip circuit breakers often have a wider Temperature range (-20°C – 55°C) and so are less susceptible to ambient temperature fluctuations. At very low temperatures, the mechanical parts of the trip unit could require special lubrication.
At very high temperatures, the electronic circuitry components could be damaged. Some MCCBs with electronic trip units have special self-protection circuitry to trip, should the internal temperature rise to an unsafe level.
An atmosphere with high moisture content or the presence of corrosive elements should be avoided. Electrical equipment should be mounted in clean and dry environments.
If moist conditions cannot be avoided, special fungus treatments may be necessary. While the glass-polyester molded cases may not support the growth of fungus, terminals and other parts may. If changes in temperature create condensation, space heaters in the enclosures may be required.