Miniature Circuit Breaker (MCB) are designed to protect the conductors and insulation from damage due to over load and short circuit.The simplest way to visualize a miniature circuit breaker is to think of a load center in a home, the circuit breakers inside are miniature circuit breakers.
Components
MCBs are made up of 5 components :
- Molds/Mounting
- Type Handles / Armatures
- Magnetic & Bimetal Protection
- Line side terminal / Clip
- Load side terminal
Mounting
Mounting of Miniature Circuit Breaker :
- Plug-In
- Used in Residential applications.
- The line-side terminal is a clamp that clips onto a bus stab in the load center or panelboard. The load-side terminal is the cable-out.
- Bolt-On
- Used in commercial and industrial applications.
- The line-side terminal is an extended tang that is bolted onto panelboard bus. The load-side terminal is cable out.
- Cable-In/Cable-Out
- Used in industrial applications.
- The line-side and load-side electrical connections are by cable.
Types of Protection
There are four types of Circuit Protection:
- Overload / Thermal Uses a circuit breaker to terminate power to the circuit if an overload / overcurrent event occurs.
- Ground Fault Uses Ground Fault Circuit Interrupter (GFCI) to detect currents flowing outside the current carrying conductors which could cause harm to people or equipment.
- Short Circuit / Magnetic Uses a circuit breaker to clear an electrical fault that is created when two exposed conductors touch or when a conductor’s insulation fails.
- Arc Fault Uses Arc Fault Circuit Interrupters (AFC!) to detect unwanted or intermittent flow of current between two conductors that can damage nearby combustible material thereby starting a fire
Where are MCBs used?
Miniature circuit breakers are installed in residential, commercial and industrial load centers, lighting panelboards or individual mounting applications.
Although miniature circuit breakers have accessories to help customize them for certain applications, they do not have any replacement parts. They are not designed to be repaired. When the unit goes bad, it must be replaced.
Types of Miniature Circuit Breakers (MCB’s)
MCBs are classified into three major types according to their instantaneous tripping currents. They are
- Type B MCB
- Type C MCB
- Type D MCB
Type B MCB
This type of MCB will trip instantly at a rate of three to five times its rated current. These are normally used for resistive or small inductive loads where switching surges are very small. Therefore, these are suitable for residential or light commercial installations.
Type C MCB
This type of MCB will trip instantly at a rate of five to ten times its rated current. These are normally used for high inductive loads where switching surges are high such as small motors and florescent lighting. In such cases, type C MCBs are preferred to handle higher value of short circuit currents. Therefore, these are suitable for highly inductive commercial and industrial installations.
Type D MCB
This type of MCB will trip instantly at a rate of ten to twenty five times its rated current. These are normally used for very high inductive loads where high inrush current are very frequent. These are suitable for specific industrial and commercial applications. The common examples of such applications include x-ray machines, UPS systems, industrial welding equipment, large winding motors, etc.