How to Select the Right Molded Case Circuit Breaker?

FEBRUARY 23,

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Table of Contents

1. Types of Molded Case Circuit Breakers
2. How Are Molded Case Circuit Breakers Rated?
3. How Do I Choose The Right MCCB?
4. How Do I Know What Size Circuit Breaker I Need?
5. Conclusion

Unless you choose a molded case circuit breaker (MCCB) of the right type and rating, the device will either trip too soon or too late. In both scenarios, the choice of the wrong unit can lead to safety issues, power distribution problems, and possible equipment damage and losses.

Choosing the right type of MCCB with a rating meant for your intended application is crucial as it  helps maintain the safety of your workers and equipment while also ensuring that the system runs with optimum efficiency.

In this guide, we will discuss the types of molded case circuit breakers and how to select the appropriate one for your application.

Types of Molded Case Circuit Breakers

MCCB manufacturers provide performance details such as amp rating, short circuit rating, and whether the unit is current limiting or non-current limiting (standard) breaker. However, the unit type isn’t based on these metrics but on the tripping curves.

A trip curve is a graphical representation of how a circuit protection device behaves in response to current levels. Based on this, MCCBs are segregated into five categories:

Type B

The second most sensitive of all MCCB types, products in this category trip at 3 to 5 times the rated current of the unit and have a tripping time of 0.04 to 13 seconds.

This makes Type-B MCCBs well-suited for resistive applications in residential and light industrial setups. Because the surge current level of these MCCBs is relatively low, they are ideal for resistive elements and loads, such as light fixtures and domestic appliances.

Type C

A step above Type B MCCBs, Type C units trip at 5 to 10 times their rated current. This makes them suitable for use in commercial and industrial applications where there is a possibility of short circuit currents in the electrical system.

Their tripping time is between 0.04 to 5 seconds, and they can handle higher surges, so they work well in industrial settings with small inductive loads such as electromagnets, pumps, small to mid-sized motors, fluorescent lights, and transformers.

Type D

Their tripping time is between 0.04 to 5 seconds, and they can handle higher surges, so they work well in industrial settings with small inductive loads such as electromagnets, pumps, small to mid-sized motors, fluorescent lights, and transformers.

For example, Type D MCCBs are an ideal choice for industrial settings involving large battery charging, large winding motors, discharge lighting and X-ray machines, and other such medical/radiological equipment, etc.

Type K

For example, Type D MCCBs are an ideal choice for industrial settings involving large battery charging, large winding motors, discharge lighting and X-ray machines, and other such medical/radiological equipment, etc.

This makes them suitable for handling inductive and motor loads where a high starting current is expected.

Type Z

The most sensitive of all types of MCCBs, Type Z units will trip at 2 to 3 times their rated current. The tripping time is 0.04 to 5 seconds, which makes them an ideal choice for exceptionally sensitive devices that are easily damaged even by low current surges. Typically, such units are used in systems serving semiconductor-based IT and medical equipment.

 

How Are Molded Case Circuit Breakers Rated?

MCCBs are rated based on multiple variables, and each of these impacts their performance. Manufacturers offer accurate data pertaining to these ratings, which include:

• Rated frame current/Frame size (Inm): This indicates the size or the dimension of the plastic casing or shell of the unit. Also, it is indicative of the maximum current that the casing/shell of the unit can handle.
• Rated current (In/Ie): This is the functional range of the unit or the maximum current value above which the unit will trip.
• Rated voltage (Ue): This is the functional voltage of the breaker or the continuous operating voltage that the unit is designed for. Typically, this value is close to or the same as the standard system voltage.
• Rated insulation voltage (Ui): This is the maximum voltage range that the unit can resist, as per laboratory tests. This value is usually higher than the rated voltage to allow for a margin of safety.
• Rated Impulse Withstand voltage (Uimp): This is the transient surge voltage that the unit is designed to handle. Testing is done at a standard size of 1.2/50Âs. So, a rating such as Uimp=8kV means that the unit was tested at a peak current of 8kV at a standard size of 1.2/50.
• Unlimited short circuit breaking capacity (Icu): This is the maximum fault current that the breaker will clear, but there is a likelihood that the unit may get permanently damaged in the process.
• If the fault current exceeds this value, the breaker may not trip, and it will get permanently damaged. This is a factor that impacts the cost of the unit. The breaking capacity should be higher than the possible fault current level. For residential applications, going above 10kA would be good enough.
• Short circuit Breaking Capacity (Ics): This is typically a percentage of the Icu and refers to the maximum fault current at which the unit will trip without suffering permanent damage. Typically, this refers to a fault level at which the unit can trip three times and yet be reusable after a reset. The higher this value, the more reliable the unit is.

To understand how these ratings work, consider the example of a breaker that has:

• Icu: 40,000 Amperes
• Ics: 25,000 Amperes

This breaker will clear a fault below 25kA without any problem. However, if the fault level is between 25 kA and 40 kA, the fault will be cleared, but the breaker most likely will get permanently damaged in the process.

If the fault level exceeds 40kA, the unit will not clear the fault, and another mechanism/device will be required for circuit protection.

In addition to these manufacturers’ ratings, when buying a molded case circuit breaker, it is also crucial to ensure that they are designed and tested to meet various quality, performance, and/or reference standards and certifications such as:

• The UL489 standard for molded case circuit breakers
• The NEMA AB-1
• The IS - 1/ 2
• The IEC - 1/ 2
• Testing authority certificates: KEMA, ASTA, TUV
• Location-specific certifications: DEKRA, CCS, CE, and others.

Given the extremely important role that MCCBs play in the safety and performance of electrical systems, additional testing is vital to ensure that the unit is operating as expected. Such tests should include:

• Insulation resistance test: This helps gauge the insulation level between individual phases and between supply and load. The MCCB is isolated to perform this test. The resistance measure must exceed the manufacturer’s guide to get the required level of protection.
• Contact Resistance Test: This shows if the unit is functioning as required by gauging the resistance across poles. The unit should have a very low voltage drop.
• Overload Tripping Test: With this, an electrician can test the overload tripping of the unit. This is done by applying 300% of the breaker rating to each contact.
• Thermal Protection Test: An overcurrent that is 3 to 4 times the rated current of the unit is applied to the breaker to gauge the level of protection offered in overload conditions.
• Thermal Protection Test: An overcurrent that is 3 to 4 times the rated current of the unit is applied to the breaker to gauge the level of protection offered in overload conditions.
• Other tests may also be used to ensure the proper functioning of the breaker. A wide variety of testing equipment and testing techniques are required to conduct these tests. It goes without saying that the professional conducting these tests will need an in-depth understanding of how MCCBs work and the relevance and impact of various reference values.

How Do I Choose The Right MCCB?

When selecting a molded case circuit breaker for a specific application, consider these 5 factors:

1. The frame size: It is crucial to pick a unit with appropriate dimensions for the available space. Usually, the same frame size is available with various current ratings, so consider the availability of space and the line’s calculated load when picking the correct unit. The rated current classification is usually chosen based on the priority coefficient (1.25).
2. Rated insulation voltage: This reference value should be used to determine the creepage as well as clearance distance. If the rated insulation voltage has not been provided, use the rated working voltage for this calculation.
3. Rated current: For MCCBs, the rated current is not a fixed value, as it is possible to adjust the amp trip below the maximum overload protection current.
4. Ultimate Short-Circuit Breaking Capacity (Icu): Many MCCBs offered for domestic application have different Icu for the rated current of a frame level. When selecting the unit, it is crucial to ensure that the expected short circuit current is below the Icu to ensure that in case of a fault, the unit can handle the fault current without being damaged.
5. Shunt trip for protection relays: When an MCCB trip due to an external signal from a protection relay, it is known as a shunt trip. If such protection relays (sensors) are part of the electrical system, you must choose an MCCB that accepts inputs from such sensors.

How Do I Know What Size Circuit Breaker I Need?

An MCCB should be sized based on both the operating current as well as fault currents. In order to do so, you need to consider 3 criteria:

• The rated working voltage: This has been defined above. When choosing a unit, ensure that the working voltage is similar to the system’s voltage.
• The trip value: Make sure that the trip range of the MCCB allows for the adjustment of the unit to respond appropriately to the current drawn by the load.
• The breaking capacity: Choose a unit with a breaking capacity higher than all possible fault currents for a system.

Conclusion

Molded case circuit breakers offer excellent protection against overcurrents, short circuits, and other faults that could harm a system. The most important thing to remember when choosing an MCCB is to pick the right size, trip value, and breaking capacity for your particular application. Make sure to research the capabilities of each unit before making a purchase decision. 

If you are looking for high-quality molded case circuit breakers, Chint Global is your ideal partner. With our vast experience and expertise in the industry, we can help you select the perfect unit for your specific application. We also offer a wide range of other electrical products that meet the highest quality standards. Contact us today to learn more about our products and services.

Have you ever wondered what keeps your factory floor humming, your commercial building running, or components ensuring reliable power management? Did you know that U.S. electricity customers experienced an average of approximately five and one-half hours of power interruptions? It’s not just about wires and switches. It’s those circuit breakers, specifically molded case circuit breakers (MCCBs). These devices might not get much attention, but they are essential in preventing power disruptions, equipment failures, and even catastrophic electrical accidents.

Without MCCBs, even a minor electrical fault could pause operations, damage expensive equipment, and lead to significant downtime. 

In industries where uptime and reliability are everything, having the proper circuit protection in place is non-negotiable. But what exactly makes MCCBs a necessity for modern electrical systems? Let’s get deeper into the topic to understand their features, types, and benefits and why they should be on your radar for industrial and commercial power solutions. 

What Is a Molded Case Circuit Breaker (MCCB)? 

A molded case circuit breaker (MCCB) is an electrical protection device that protects circuits from overloads, short circuits, and other electrical faults. MCCBs offer a higher capacity to handle larger currents, making them suitable for industrial and commercial applications. 

MCCBs get their name from the molded insulating case that houses the internal components. This durable casing protects the breaker from external damage and environmental factors, ensuring long-term reliability.   

MCCBs support adjustable trip settings, allowing users to customize the breaker to different load requirements and making them highly versatile for various applications. 

The Features of Molded Case Circuit Breakers  

Molded case circuit breakers (MCCBs) stand out for their ability to handle high currents and provide customizable protection for electrical systems. Here’s a detailed look at their essential features.  

Adjustable Trip Settings: Allows fine-tuning of trip thresholds for different load requirements, offering flexibility in protection.

High Current Rating: Handles a wide range of currents, typically from 16A to over 1,600A, making it suitable for low- and high-power circuits.

Durable Molded Case: Ensures internal components are protected from dust, moisture, and mechanical impacts, enhancing breaker longevity.

Thermal-Magnetic Trip Mechanism: Combines thermal protection for overloads and magnetic protection for short circuits to improve safety.

Broad Voltage Range Compatibility: Operates across various voltage levels, up to 1,000V, making it versatile for different systems.

Longevity and Reliability: Withstands multiple trips without performance issues, ensuring reliable long-term use.

Compliance with Safety Standards: Meets international standards such as IEC -2 or UL 489, ensuring performance and regulatory compliance.

How Does the Molded Case Circuit Breaker Work?

Molded case circuit breakers protect electrical circuits by automatically disconnecting power when faults like overloads or short circuits occur. Their operation involves three essential mechanisms: thermal protection, magnetic protection, and manual operation. 

Thermal Protection 

The thermal protection mechanism works through a bimetallic strip inside the MCCB. When an overload arises, the strip heats up and bends. This action trips the breaker, disconnecting the circuit to prevent damage from prolonged high currents. The thermal mechanism ensures that even gradual overloads, which may not immediately cause harm, are detected and addressed. 

Magnetic Protection

The magnetic protection mechanism activates during short circuits. A sudden surge in current creates a strong magnetic field within the MCCB, pulling a solenoid that instantly trips the breaker. This rapid response is crucial for preventing catastrophic damage to equipment and reducing fire risks.   

Manual Operation 

MCCBs have a manual operation feature, allowing operators to manually switch the breaker on or off for maintenance or safety issues. Modern MCCBs may also include remote control capabilities through integration with automated systems. 

Once tripped, the breaker must be reset manually or remotely. MCCBs operate in cycles, continuously monitoring the circuit for faults and ready to trip when abnormal conditions occur. This combination of thermal and magnetic protection ensures comprehensive safety for gradual and immediate faults.

Types of MCCBs

Let’s take a closer look at the different types of MCCBs and how they can be applied in various environments to ensure the safety and reliability of your electrical systems. 

If you are looking for more details, kindly visit mold case circuit breaker supplier.

Thermal MCCBs 

Thermal MCCBs protect circuits from overloads. They use a bimetallic strip that bends when it heats up due to excessive current flow. The bending of the strip triggers the breaker to trip, disconnecting the circuit and preventing damage from prolonged overcurrent. These types are ideal for applications where slow-to-develop overloads are common.

Magnetic MCCBs

Magnetic MCCBs offer protection against short circuits. They feature a solenoid that generates a magnetic field in response to a sudden surge in current. When this magnetic force exceeds a preset threshold, it pulls the trip mechanism and disconnects the circuit. Magnetic MCCBs respond instantly to faults, making them suitable for high-risk electrical environments where fast fault clearing is essential.   

Thermal-Magnetic MCCBs 

Thermal-magnetic MCCBs combine the features of both thermal and magnetic protection mechanisms. These MCCBs offer two levels of protection: thermal protection for gradual overloads and magnetic protection for quick trips during short circuits. They are commonly used in applications requiring thorough protection against various fault conditions. 

Electronic MCCBs 

Electronic MCCBs use digital sensors and microprocessor-based control systems to monitor the current and other electrical parameters. These MCCBs offer highly accurate protection, faster tripping, and the ability to adjust settings remotely. They are ideal for applications where precise control and monitoring are crucial, such as in critical infrastructure and sensitive equipment.

High-Interrupting Capacity MCCBs  

High-interrupting capacity MCCBs can handle huge fault currents. They are used in industrial settings where high-power circuits exist, ensuring that even extreme faults are safely interrupted. These MCCBs have advanced arc quenching technology to handle high-intensity short circuits.

Fixed MCCBs 

Fixed MCCBs have preset trip settings and cannot be adjusted once manufactured. They are typically used in environments with stable and predictable current requirements. These breakers are simple and reliable, often used in low-risk, low-maintenance applications.

Adjustable MCCBs 

Adjustable MCCBs provide the flexibility to set trip thresholds according to the specific needs of the circuit. These MCCBs allow operators to fine-tune the protection settings for optimal performance. They are ideal for applications where load conditions may change, such as motor protection or industrial equipment with varying current demands. 

Understanding the Characteristics and Ratings of MCCBs

MCCB manufacturers provide the specifications that define the operational capabilities of each breaker. Below are some of the critical parameters that help determine the right MCCB for a specific application: 

Rated Frame Current (Inm): This indicates the maximum current the MCCB can handle. It establishes the upper limit for the adjustable trip current range and determines the size of the breaker frame. 

Rated Current (In): This value signifies the current level at which the MCCB will trip to protect against overloads. It is adjustable within the range of the rated frame current.

Rated Insulation Voltage (Ui): It is the maximum voltage the MCCB can resist under laboratory conditions. The operational rated voltage is generally lower than this to ensure a safety margin.   

Rated Working Voltage (Ue): This refers to the voltage at which the MCCB operates continuously, typically matching or closely aligning with the system’s voltage.  

Rated Impulse Withstand Voltage (Uimp): This rating refers to the transient peak voltage the MCCB can withstand due to switching surges or lightning strikes. It determines the breaker’s ability to handle brief, high-voltage events. The standard test size for impulse is 1.2/50µs.

Operating Short Circuit Breaking Capacity (Ics): This value represents the highest fault current the MCCB can handle without sustaining permanent damage. MCCBs that don’t exceed this capacity are typically reusable after a fault interruption, ensuring greater reliability. 

Ultimate Short Circuit Breaking Capacity (Icu): This is the maximum fault current an MCCB can manage. If the fault current surpasses this value, the breaker cannot trip. In such cases, an alternative protection device must be used. The Icu value is crucial for assessing the reliability of the MCCB during fault conditions.  

It’s important to note that if the fault current is higher than Ics but lower than Icu, the MCCB can still interrupt the fault but may sustain damage and need replacement.   

Mechanical Life: This represents the maximum number of manual operations the MCCB can endure before failure.

Electrical Life: This denotes the maximum number of trips the MCCB can make before it fails due to wear.

Applications of MCCBs Across Industries 

Molded case circuit breakers (MCCBs) are widely used across various industries due to their versatility, reliability, and ability to protect electrical circuits from overloads and short circuits. Here are some significant applications of MCCBs across different sectors:   

Industry Sector Application Benefit Industrial Manufacturing Protects electrical circuits for heavy machinery and equipment. It prevents production disruptions and protects expensive machinery. Commercial Buildings Safeguards electrical panels in office buildings, shopping malls, and data centers. Prevents electrical hazards and fire. Power Generation & Distribution Protects power plants, transformers, and distribution systems. Ensures stable power supply and prevents damage to critical infrastructure. HVAC Systems Protects electrical circuits for heating, ventilation, and air conditioning systems. Protects HVAC equipment from overloads.  Transportation Infrastructure Protects power circuits in railway stations, airports, and ports. Ensures smooth operations in critical transportation sectors. Renewable Energy Protects components in solar power installations and wind farms. Ensures operational safety and protects inverters and batteries. Residential Applications Provides overcurrent protection in home electrical panels. Safeguards household electrical systems and prevents potential hazards. Marine and Offshore Protects electrical circuits in ships and offshore rigs. Ensures safety in harsh environments and fluctuating power loads.

Benefits of Using MCCBs

Molded case circuit breakers (MCCBs) provide numerous benefits that enhance the safety and efficiency of electrical systems. Here are some of the main advantages of using MCCBs: 

• Overload Protection: MCCBs protect electrical circuits from overloads, preventing damage to wires and devices due to excessive current flow.
• Short Circuit Protection: MCCBs can handle short-circuit conditions and trip the circuit to prevent further damage to equipment, wires, and the entire electrical system.
• Adjustable Trip Settings: MCCBs offer adjustable trip settings, allowing users to fine-tune the protection for specific applications based on the current rating and system requirements. 
• Reliable Performance: With high breaking capacities, MCCBs can handle significant fault currents, ensuring they can withstand and clear faults without getting damaged.
• Compact Design: Their compact size makes MCCBs suitable for installation in smaller electrical panels, helping save space while maintaining effective protection. 
• Enhanced Safety: MCCBs feature mechanisms like thermal and magnetic tripping functions, significantly reducing the risk of electrical fires and other hazards.
• Durability: These breakers last longer than fuses, with a higher mechanical and electrical life, reducing the frequency of replacements. 
• Easy Reset: Unlike fuses that need to be replaced after tripping, MCCBs can be easily reset after they have been tripped, saving time and money. 
• Versatility: Available in a wide range of current ratings, MCCBs are versatile and suitable for various industries, including industrial, commercial, residential, and critical infrastructure.  
• Regulatory Compliance: MCCBs meet various national and international standards, ensuring compliance with safety regulations and improving the overall safety of electrical systems.  

Factors to Consider When Selecting the Right MCCB for Your Electrical System

Selecting the right molded case circuit breaker is vital for ensuring the safety and efficiency of your electrical system. Here are some fundamental factors to consider when choosing an MCCB: 

Current Rating   

Ensure the MCCB’s current rating matches the maximum load your system will carry. The breaker should be able to handle the full range of currents expected in your electrical system, including any potential overloads. Consider the Rated Frame Current (Inm) and Rated Current (In) to determine the size and trip settings of the breaker.

Breaking Capacity

The MCCB must have a breaking capacity that is high enough to handle fault currents that could occur during a short circuit. Examine the Ultimate Short Circuit Breaking Capacity (Icu) and Operating Short Circuit Breaking Capacity (Ics) to ensure it can effectively handle short circuits without failure.

Voltage Rating

The voltage rating should match or exceed the operating voltage of your system. Ensure the MCCB’s Rated Working Voltage (Ue) suits the intended application. The Rated Insulation Voltage (Ui) indicates the maximum voltage the breaker can resist in lab conditions, providing a safety margin.

Trip Characteristics

Based on your system’s load and application type, select an MCCB with appropriate trip characteristics. Thermal-magnetic MCCBs are commonly used for general protection, while electronic MCCBs provide faster, more accurate tripping for sensitive systems.

Size and Mounting Requirements

Choose an MCCB that fits within your electrical panel. Check for compact designs if space is limited. Ensure that it complies with mounting and installation standards for your specific setup.

Compliance with Standards

Make sure that the selected MCCB meets local safety standards and regulations. Depending on your region, it should be certified by relevant regulatory bodies such as UL, IEC, or ANSI.

Maintenance and Durability

Look for MCCBs with a long service life and minimal maintenance. Some are rated for more operations, which can be beneficial in high-demand environments.

Cost vs. Performance

Evaluate the cost of the MCCB relative to the protection it provides. While it’s tempting to opt for cheaper options, it’s crucial to prioritize safety and long-term performance. A more expensive MCCB may offer better protection and longer life, saving you money on repairs and replacements.

Best Practices for MCCB Maintenance 

MCCBs are made to handle high currents, making regular maintenance essential for ensuring their reliable operation. Below are some maintenance procedures to follow:

1. Visual Inspection

Conduct a thorough visual inspection of the MCCB to check for any signs of damage, such as deformed contacts, cracks in the casing or insulation, or burn marks. These indicators can suggest wear or electrical faults and should be addressed immediately.

2. Lubrication

Some MCCBs require periodic lubrication to maintain smooth operation. Focus on lubricating the manual disconnection switch and any internal moving components to prevent friction and ensure proper functionality.

3. Cleaning

Regularly clean the MCCB to remove dust and dirt that can impair its components. Any dirt containing conductive materials can create a current path that might lead to internal faults. Keeping the breaker clean reduces the risk of malfunctions.

4. Testing

Get the following tests done by professionals to guarantee that the MCCB remains in optimal conditions:  

• Insulation Resistance Test: Disconnect the MCCB and measure the insulation resistance between the phases and across the terminals. If the resistance is below the manufacturer’s recommended level, the MCCB will not provide sufficient protection.
• Contact Resistance Test: Measure the resistance across the electrical contacts and compare it to the manufacturer’s specifications. Under normal operating conditions, contact resistance should be low to minimize energy loss and ensure efficient operation.
• Tripping Test: This test checks the MCCB’s response to overcurrent and fault conditions. Test the thermal protection by running a current 300% above the rated value. If the breaker does not trip, the thermal protection is compromised. For magnetic protection, subject the MCCB to high-current pulses. Magnetic protection should trip instantaneously under these conditions. Perform this test last, as high currents can alter the results of the previous two tests by increasing the temperature of the contacts and insulation.

Regular maintenance and testing help ensure the continued reliability and longevity of the MCCB, preventing costly breakdowns and ensuring the electrical system’s safety.

Why Should You Choose LS Electric America for Your MCCB  Needs?  

At LSElectric America, we offer the Susol UL Molded Case Circuit Breaker (MCCB) — a strong solution designed to meet the highest standards of safety, performance, and reliability. Whether you’re looking for enhanced protection for industrial, commercial, or critical infrastructure applications, the Susol UL MCCB delivers.

Features of Susol UL MCCB  

• Wide Range of Rated Currents: 15A to A
• High Breaking Capacity (Icu): 25kA to 100kA
• Service Breaking Capacity (Ics): 100%
• Certified Standards: UL489, CSA, IEC -2 CB, and Class 1E for nuclear power plants

Applications 

Susol UL MCCBs are perfect for:  

• Industrial machinery and systems
• Commercial buildings and power distribution networks
• Important infrastructure requiring UL-certified circuit breakers

Explore Advanced Circuit Protection with LSElectric America Inc.

When it comes to protecting your electrical systems and ensuring operational safety, LSElectric America Inc. leads the way with advanced solutions designed to meet the highest standards. Our extensive portfolio of Molded Case Circuit Breakers (MCCBs) and other critical electrical components ensures your systems stay safe and efficient under varying conditions. 

Whether you’re looking for superior fault protection, enhanced system reliability, or energy-efficient solutions, our MCCBs are built to deliver.

Our offerings include: 

• • MCCBs for Maximum Protection
  • Panel Control Solutions
  • Power Distribution
  • Automation & Drives
  • Renewable Energy

With a focus on performance, durability, and ease of integration, our solutions are perfect for various industrial applications. 

Partner with LSElectric America Inc. today and improve the reliability and safety of your electrical infrastructure.
Contact us today!