Table of Contents

1. What is a Molded Case Circuit Breaker
2. Molded Case Circuit Breaker Application
3. Molded Case Circuit Breaker Ratings
4. Molded Case Circuit Breaker Vs Traditional Circuit Breaker
5. Conclusion

Molded Case Circuit Breakers (MCCB) is a required component of electrical systems, providing overload protection and short-circuit protection. In most cases, MCCBs are installed in the main power distribution board of a facility, allowing the system to be easily shut down when necessary. MCCBs are available in various sizes and ratings, depending on the size of the electrical system.

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In this guide, we'll cover the components and features of a typical MCCB, how they work, and which types are available. We'll also discuss the benefits of using this type of breaker in your electrical system.

What is a Molded Case Circuit Breaker

A molded case circuit breaker, or MCCB, is a safety device used to protect an electrical circuit from overload or short circuits. It works by automatically cutting off the power supply when a fault or overcurrent situation arises, thus preventing any damage to the electrical system. MCCBs can be used in both low-voltage and high-voltage systems.

In addition to providing protection against faults, they also provide isolation of the circuit for maintenance. MCCBs are typically installed in the distribution panel and provide a visible indication to let users know when the power is off.

The main components of an MCCB are:

Molding Case

The molded case or frame is the cushion that keeps all parts of the circuit breaker in place. It is solidly built from 'glass polyester' or 'thermoset composite resin that gives a great nonconducting strength despite its compressed size.

Terminals

The terminals serve as connectors between external conductors and molded cases. They should be connected properly to prevent unusual heat production.

Operating Apparatus

This is the switch that opens and closes the molded case. Its handle connects the pull of the device and manual push.

Trip 'Unit

The Trip System is composed of temperature and current-reactive electromagnetic sensors that trigger the Operating Apparatus in case of short-circuit or current overloads. Its button can be pressed to reset the circuit breaker.

Arc Chamber

The Arc Extinguisher's primary role is to curb and split the arc that can damage your circuit breaker. The action results in exterminating the current flow in the circuit breaker. Inside the arc chamber are contacts. Their role is to conduct and disrupt functions. Arc 'Runners, on the other hand, function as new electrodes for the arc. Arc chutes, on the other hand, compress the arc in the middle of sidewall insulators.

 

Molded Case Circuit Breaker Application

On application, MCCBs are designed to handle high currents, especially on expensive equipment. You will often find MCCB used commonly used in industrial-levels of machinery such as the following:

Motors

MCCBs protect motors by having their settings modify the inrush current and give the delay it may need. When done correctly, the motors are protected from overloads without triggering the tripping mechanism.

Welding Machinery

Welding machines utilize high currents, which normal circuit breakers cannot handle. An MCCB can be used to protect welding machines by connecting the machine to its own circuit breaker.

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Generators

It is widely known that generators produce high levels of amps and need costly gen-sets. To shield the linked circuits and generator from faults that may happen in the system, having an MCCB is essential as it can handle its high current ratings and protects your generators as needed.

Capacitor Banks

MCCB lessens the currents, which in turn, corrects the 'power factor' in commercial and industrial-level systems.

Modifiable Trip Modes

These settings allow MCCBs to be utilized in low-current appliances in the household. This makes it an all-rounder use as it can be adjusted between low and high-current settings.

Electric Feeders

MCCB has adjustable settings that can be adjusted and allows it to handle high currents. If applied to electric feeders that produce hundreds of amps, MCCB can dissipate these energies easily. It also acts as its primary 'incoming breaker.

Molded Case Circuit Breaker Ratings

Molded case circuit breakers (MCCBs) have a variety of ratings that determine their performance and suitability for different applications. Some of the main molded case circuit breaker ratings include:

• Rated Current (In) is the exceeding value when the overload protection reaches its tipping point. You can modify these values in MCCB.
• Rated Frame Current (Inm) is the maximum capacity value of the MCCB and dictates its 'physical form.
• Rated Insulation Voltage (Ui) is the maximum current MCCBs can handle as evidenced by the conducted tests. It is greater than the rated working voltage to give an allocated safety margin while in use.
• Rated working voltage (Ue) is the uninterrupted operating voltage of MCCB. This is usually equal to or near the standard level of system voltage.
• Operating short-circuit breaking capacity (Ics) is the maximum 'fault current that MCCB can 'trip without permanent damage. You can continue using the MCCB after a fault interruption, provided it doesn't go beyond the limits.
• Mechanical life is the number of times you can operate the device manually before it dysfunctions.
• Electrical life is the estimated number of times the MCCB can 'trip before it completely becomes unusable.

A molded case circuit breaker (MCCB) is a kind of protection device for electrical circuits. It works by preventing excessive current flow in the circuit thereby safeguarding the device it is connected to against risks like short-circuiting and electrical overload.

Let us get to know more about these crucial protection devices in this ultimate guide to molded case circuit breakers.

How does the MCCB work?

An MCCB combines a magnetic component (an electromagnetic device which is current sensitive) with a thermal component (a device sensitive to temperature). This allows the trip mechanism. Following this mechanism, the MCCB can provide

1. Electrical fault protection against short-circuiting
2. Protection against overloading, and
3. Electrical switch for emergency disconnection.

Understanding MCCB features and ratings

All manufacturers of MCCBs are mandated to mention the operational features of the products they are offering. Some of the most common features of MCCBs are listed below:

1. Rated Current (In): the tripping point of the MCCB during overload protection.
2. Rated Frame Current (Inm): the maximum current that the device can handle. It determines both the frame size of the breaker and the upper limit of the rated current.
3. Rated Working Voltage (Ue): the rated voltage for the constant use of the MCCB.
4. Rated Insulation Voltage (Ui): the highest voltage that the MCCB can protect against in laboratory conditions.
5. Rated Impulse Withstand Voltage (Uimp): This value represents the circuit breaker's ability to endure transient peak voltages resulting from switching surges or lightning strikes, thus determining its resilience against transient over-voltages.
6. Ultimate Short Circuit Breaking Capacity (Icu): the maximum fault current value that the MCCB can withstand.
7. Operating Short Circuit Breaking Capacity (Ics): The maximum fault current that the MCCB can withstand before being permanently damaged. The higher this value, the more robust the MCCB.
8. Note that in case the fault current is more than the Ics but less than the Icu, the MCCB will still be able to operate. However, it will need to be replaced soon.
9. Electrical Life: the maximum number of trips the MCCB can withstand before becoming non-operational.
10. Mechanical Life: the maximum manual operations allowed before the MCCB fails.

Different Types of MCCBs

There are several molded case circuit breaker types available in the market, some of which are as follows:

1. Type B: This type of molded case circuit breaker trips between 3-5 times the rated current. Tripping time is 0.04-13 seconds. These mostly have resistive, domestic applications and can handle low surge currents.
2. Type C: These trip between 5-10 times their rated current. Tripping times fall within the range of 0.04-5 seconds. Applications involve relatively modest inductive loads, such as small motors, transformers, and electromagnets typically used in industrial settings. Suitable for higher surges.
3. Type D: Type D MCCBs are known to trip between 10-20 times their rated current, and their tripping time ranges from 0.04 to 3 seconds. These MCCBs exhibit the highest surge tolerance and are thus selected for applications with extremely inductive loads like large electrical motors commonly found in industrial environments.
4. Type K: These trip when the current reaches 10-12 times their rated current. Tripping time falls between 0.04 to 5 seconds. Applications involve inductive loads like motors.
5. Type Z: Type Z MCCBs are the most sensitive among MCCBs, tripping when the current reaches only 2-3 times their rated current. They have the shortest tripping time and are employed for applications where extreme sensitivity is essential. This includes protecting semiconductor-based medical equipment and other costly devices that are susceptible to low current surges.

The Different Testing Methods for MCCBs

A common doubt regarding MCCBs is how to test the MCCB breaker. Three tests are essential and highly effective for this purpose and they are:

• The insulation across load and supply terminals as well as between phases must be tested. This value should not be less than the insulation resistance value recommended by the manufacturer.
• Testing the resistance of the electrical contacts is essential. The value should be extremely low.
• Tripping tests have to be undertaken. Thermal power testing involves passing a huge current through the MCCB. If the MCCB does not trip, it is faulty. Magnetic protection capacity is tested by passing a very strong current in short pulses. Magnetic protection should be instantly achieved if the MCCB is working properly.

Read Also - 5 Differences Between Mcb and Mccb

Best Quality MCCBs Available at the Schneider Electric eShop

Now that you have a comprehensive idea regarding MCCBS, their types, what is breaking capacity in MCCB, and the steps for testing circuit breakers, you might want to scan the market for the best MCCBs suited to your project. When purchasing electrical equipment, it is best to opt for reliable brands to ensure complete safety.

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