What is a MCCB?
As MCBs are used for motor feeders, they are referred to as miniature circuit breakers as they can handle up to 100 amps. The motor feeders use MCCBs (factually molded case circuit breakers) for between 250 and 800 amps. This system of circuit breakers prevents overloading and short circuit issues caused by overloading the electrical system. MCCBs, commonly known as circuit breakers with adjustable trip settings, are most commonly used with wide voltage ranges, as they can handle currents up to 2500 volts.
The MCCB, also known as a miniature circuit breaker or MCCB, is widely used in low voltage electrical networks instead of fuses as its handling is electrically safer than using a fuse, so it automatically shuts down electrical circuits during abnormal conditions. This guide is all about mccb with all the exciting facts.
Components and Specifications of MCCB
MCCB is composed of four major components:
1. The frame
In addition to providing insulated housing for all circuit breaker components, it is sometimes called a molded case. The compact design allows for high dielectric strength in a thermoset composite resin or glass polyester. In addition, the breaker’s characteristics (maximum voltage and current ratings) are described by the designation based on the type of molded case.
2. The trip unit
The Trip Unit controls circuit breakers. Short circuits or sustained overloads trigger the tripping mechanism, which trips the operating mechanism. A conventional molded case circuit breaker uses an electromechanical trip unit. Combined with a current-sensitive electromagnetic device, a circuit breaker is protected mechanically through the use of temperature-sensitive devices.
Electronic trip units are now available that can provide much more advanced monitoring and protection than traditional electronic trip units.
To provide circuit protection for various applications, molded case circuit breakers usually contain one or more different trip elements. These trip elements can prevent a thermal overload, short circuit, and arcing ground fault.
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Two types of electromechanical trip units are commonly used in MCCBs: fixed and interchangeable. The real breaker must be replaced with a fixed trip breaker if its trip rating needs to be upgraded. Also known as rating plugs, interchangeable trip units can be interchanged. Interchangeable electromechanical and electronic trip units are available on some breakers.
For MCCBs to operate efficiently, they require regular maintenance, including visual inspections, cleanings, and tests.
3. Extinguisher for Arcs
Electricity breaks down, creating an arc. A circuit breaker continuously generates an arc. The purpose of an arc extinguisher is to limit and divide that arc, which in turn extinguishes it. Printed steel plates make up the arc extinguishing chamber’s interior, encased within a high-strength insulation box. As the contacts split due to an interruption, a magnetic field develops around the arc and extinguisher when current flows through the ionized area.
In the steel plates, the arc is driven into them by the lines of the magnetic field around them. Deionization of the gas and arc separation allows the arc to cool after separating. With standard MCCBs, a linear current flow is generated through the contacts, allowing a small blow-apart force to open them during a short circuit.
The mechanical energy stored in the trip mechanism accounts for most of the opening act. Current flows in both contacts in the same direction, attracting them together. New breakers commonly use a reverse loop, in which the current flows nearly in the opposite direction. Consequently, a greater force is generated when the force is applied to blow it apart. As a result of this force, the contacts are opened more rapidly, facilitating rapid arc extinguishing. There is a direct correlation between the force’s magnitude and the fault current’s magnitude. As the fault increases, the force increases, and the contacts open more quickly.
4. Mechanism of operation
The operating mechanism is responsible for opening and closing the contacts. How fast the handle is moved determines the speed at which the contacts open and close. It is possible to see the handle in mid-position if the contacts are tripped. The breaker in the on position prevents tripping and is also known as “trip-free.”
During tripping, the breaker handle must be turned off and turned on. If it is in the middle position, the handle has to be turned off before turning it on. It is helpful to find the faulted circuit when breakers are mounted in groups, such as panel boards, by moving the handle to the different positions. A few breakers have a manual trip for testing the mechanism.
If a circuit breaker attempts to pull more power than it is designed to carry, it trips. The internal detecting mechanism of the circuit breaker heats up, and trips show that the home has several heavy power appliances running simultaneously on the same circuit.
Working of MCCB
It uses a relatively robust mechanical mechanism to minimize failures and false alarms and is triggered by an overcurrent an electrical current that exceeds a designated safe current.
When an MCB is overcurrent, the bimetallic strip heats up, bends, and trips. When the switch is released, the electrical contact points are moved apart, preventing an arc (electrical discharge) from forming. The arc is divided and cooled by an insulated metal strip called an arc chute. The contacts close again as soon as the MCBs have been reset and the fault has been fixed.
The purpose of an MCB is to protect the system from overloading and short-circuiting. Each of these is detected differently using a different method. A bimetallic strip that operates thermally protects against overloads, and a coil of tripping that operates electromagnetically protects against short circuits.
If the discharge is exceptionally high, it takes one-tenth of a second for the MCB to trip (activate). It will take longer for the component to react when the overcurrent is closer to the safety limits.
Common applications of MCCB
· Low-current trip settings can be adjusted
It is possible to use MCCBs for low-current applications, even though they are typically used for high-current applications. Depending on the trip, they can be adjusted.
· Feeder protection.
When you use feeder circuits for distributing electric current, hundreds of amps can be carried on them. You may need to set up additional circuits in some instances as well. Regardless of the situation, MCCBs are a valuable tool.
· Generator protection
Their output is typically hundreds of amps, and they require expensive generators to run them. To provide the protection needed, MCCBs are used, which are capable of handling the current ratings.
· Capacitor bank protection
Industrial and commercial electrical systems are used to correct power factors. When they draw very high currents, MCCB protection becomes necessary to reduce them.
· Machines that weld
Due to the high currents drawn by some welding applications, MCCBs may be needed because miniature circuit breakers cannot handle them.