What is MCCB?
MCCB stands for Moulded Case Circuit Breaker. It is a switching device that is designed to protect electrical devices from overload and short circuits. Fault sensing arrangements are installed inside MCCBs and shunt release is provided for remote tripping of MCB.
It is available in a variety of currents ranging from 32 amps to 1600 amps and voltages ranging from 230 volts to 1.1 kV.
MCCB working principles
The MCCB system consists of two parts:
Thermal element- temperature sensing device
Magnetic element- A current sensing electromagnetic device
This device helps the MCCB to trip down for protection and isolation purposes. This enables the MCCB to provide:
- Overload Protection
- Fault Protection from short circuit
- Disconnection of electrical Switch
The MCCB provides overload protection by using temperature-sensitive elements. This component is essentially a bimetallic contact, which is a contact made up of two metals that expand at different rates when subjected to high temperatures. The bimetallic contact allows the flow of electric current via the MCCB during normal operating conditions. The bimetallic contact will bend away and start to heat due to the physical properties of the metal when the flow of current exceeds the trip value. The contact will eventually bend to the point where it physically presses on the trip bar, unlocking the contact and stopping the circuit.
Fault Protection from short circuit
MCCB provides instantaneous short-circuit response based on the electromagnetic principle. The MCCB has a solenoid coil that generates a weak electromagnetic field while an electric current passes through the MCCB. The electromagnetic field generated by the solenoid coil during normal operation is negligible. However, when a short circuit occurs in the circuit, a large current begins to flow through the solenoid, resulting in a strong electromagnetic field that pulls the trip bar and opens the contacts.
Disconnection of electrical Switch
Manual current disconnection features are also available in MCCBs along with the tripping mechanisms. An arc will be created when the contact opens.
How MCCB is made?
Internal parts of MCCB
MCCB consists of 9 different parts such
- Arc chute
- Moving Contact
- Operating mechanism
- Base cover
- Terminal Connector
- Overload trip or Bimetallic contact
- Handle knob
- Manual trip button
- CT – Current Transformer assembly
It is a stack of parallel metal plates that are mutually insulated and used to divide the arc that forms in the circuit breaker’s molded case. The arc chute is made of steel and glass fiber.
As a moving contact, an electrolyzed brass substance is used. The moving contact’s MOC (Material of Construction) should be strong arc resistance, corrosion resistance, low resistivity, and so on. The MOC determines the MCCB’s lifespan.
It covers the process of opening and closing contacts. The speed of the actuating mechanism does not depend on the speed of movement of the handle. These are called quick-create and fast-break.
It is connected to the working mechanism of the relay.
The circuit breaker is also equipped with a test mechanism to manually open the circuit breaker.
Glass fiber reinforced thermosetting polymer closure assemblies were mainly used as the bottom cover of molded case circuit breakers. This provides better mechanical strength. All parts of the MCCB are mounted inside this cover.
It is a bolt assembly made up of steel material. It is designed to make connections between the external circuit to the MCCB. It will make sure there is no loose contact between the terminals.
The terminal connector might be equipped with a spreader link assembly if the MCCB score is extra than 400Amps
Bimetallic contact is referred to as a temperature-sensitive element that consists of a combination of steel and copper. Bimetallic contact is arranged in a series with line current. It is designed to be used to trip the breaker when an overload condition occurs.
A handle knob is used to open and close the contacts manually. It won’t allow the user to stop the breaker from tripping by holding the knob at the top side and this technique is called a free trip.
The handle knob shows whether the breaker is in ON or OFF condition.
If the handle is pointing upward, it is said to be in the ON position; if it is pointing downward, it is said to be in the OFF position. If it’s tripped, the handle will be in the middle position.
Manual trip button:
The red button associated with the actuation mechanism is called the manual override (trip) button. It is mainly used to manually open circuit breakers for testing purposes.
Purpose of MCCB
MCCBs are designed to withstand high currents and are widely used in heavy-duty applications such as adjustable trip settings for low current applications, capacitor bank protection, welding machines, motor protection, generator, and electrical supply protection.
Top 10 MCCB Manufacturers
Top 10 MCCB manufacturers are
- Orient Electric
Advantages of MCCB
- Compact in size
- It protects devices from short circuits and overloads
- It provides high performance and is small in size
- Very long lifespan
Disadvantages of MCCB
- Cost is higher than MCB
- High maintenance cost
- Sensitive to dust and corrosion
What are replacements for MCCB?
Fuse: Fuse is an electrical device that is designed as a current interrupting device that opens or breaks the circuit by fusing the element in the circuit when current exceeds a certain value.
MCB: MCB stands for Moulded Circuit Breaker.
RCCB: RCCB stands for Residual Current Circuit Breaker.
ELCB: ELCB stands for Earth Leakage Circuit Breaker