Molded Case Circuit Breakers (MCCB)
Molded case circuit breakers are interrupting devices with self contained, current responsive elements. These breakers are assembled as an integral unit in a supported and enclosed housing of insulating material.
Depending on the amount of protection required, these breakers can sense internally and then clear under voltage, over current, and short circuit conditions.
Some tripping elements are also externally accessible through control wiring, and other circuit protection can be added. Breakers may rely solely on outside information to perform their prime function. Several trip units may be available for a particular frame size. A specific assembled breaker may have a lower continuous current rating than the current designation of the frame manufacturers.
Contacts often begin to part during the first cycle of a fault. The current breaker must be capable of interrupting the maximum allowable first cycle asymmetrical current. The operating mechanism provides a means of opening and closing the toggle mechanism of quick-make/ quick- break type contacts.(Snap open or closed independent of the speed of handle movement).
Molded case circuit breakers use in restricted to low voltage and medium voltage system
MCCB Trip Elements
Trip elements trip the operating mechanism of a circuit breaker during either a prolonged overload or short circuit currnent. Some molded case circuit breakers have a screwdriver slot located on the front of the trip unit used for adjusting sensitivity.
The maximum setting is established by protection of the minimum conductor size in the circuit.
Instantaneous Magnetic Trip
Magnetic trip work by using an electromagnet in series with the load current. When the current. When the current reaches the set point, the electromagnet instantaneously trips.This type of trip commonly found in low voltage breakers.
Thermal Trip
Considered the industry standard, these trip elements work using a bimetal heated by the load current.When overheated, indicating an overload, the bimetal will detect, which causes the operating mechanism to trip.Thermal Magnetic Trip
A thermal magnetic trip, in addition to provide short circuit protection, guards against long- term current overload existing longer then roughly 10 seconds. Because bimetal deection is dependent on current and time, the thermal unit provides long-time delay for light overloads and fast response for heavy overloads.
