MCB (Miniature Circuit Breakers) Guide - Types, Sizes, and Uses

What Are MCBs?

Short circuits are a term you have heard of, but have you ever wondered what happens if there is a power surge? Your devices will malfunction and even get permanently damaged. Now power surges are fairly common, so why do by our devices remain safe? The reason is a simple electro-mechanical device known as a Miniature Circuit Breaker (MCB).

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MCBs are automatic switches that automatically turn off the power supply when it detects a power surge. Earlier, this action used to be done by fuses. Though fuses have one disadvantage, they need to be replaced every time there is a short circuit. An MCB, on the other hand, can be manually restarted and is more durable.

Types of MCB

MCBs are installed in spaces depending on the need of the appliance. Hence, you will find multiple MCB types that can be used for a range of purposes. The most popular MCB types are A, B, C, D, K and Z. Of these, the most commonly used are B, C and D. These categories are often based on their trip curve or tripping capacities.

Type B - These are often used in residential properties or industrial units with small scale of operations. In such MCBs, the trip occurs when the power exceeds 5 times more than the suggested limit. These MCBs are considered to be the most sensitive owing to their lower tolerance for voltage shifts. Since, current surges and fluctuations are less intense in residential spaces, it’s mostly used in such areas.

Type C - These MCBs often trip at surges that exceed 10 times the power capacity. So these are strategically used in devices which have high power consumption requirements. Often you will find Type C MCBs in commercial and industrial units. Electrical motors and fluorescent lighting are electrical accessories where Type C MCBs are used. They offer higher protection in comparison to type B MCBs and have a higher capacity to handle surges.

Type D - Considered to be the least sensitive MCB type, the Type D has a surge capacity of 10 to 20 times higher than the power threshold. Often these are used in devices such as X-ray machines, motors and other equipment that has higher rush of power. Such expensive appliances often need added protection from fluctuations in voltage and power surges and hence these need a high capacity and robust MCB.

Read More: How Does The Mcb Protect Your Home?

Uses of MCB

Electrical panels - MCBs are installed in electrical panels to ensure there is a uniform distribution of power to all devices. An MCB also limits power fluctuations, thus ensuring less damage to equipments.

Lighting Systems - Our homes are dominated by a wide range of lights. All these lights are in use for large parts of the day. This makes it essential to install an MCB via which effective distribution of power is made possible. Certain lights need more power than others, and MCBs can regulate accordingly and offer unique lightening systems the safety they need. This safeguarding of bulbs with MCBs ensures the longevity of bulbs.

Industrial equipment and application - Industrial appliances have a heavy duty power consumption and require up to 30 kA of power supply. In addition, these appliances are expensive. Hence, MCBs maintain a constant power flow in these equipment’s. Often MCBS are installed in supermarkets, hotels and malls.

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Ground Fault Trip Mechanism - Electrical wires embedded in the earth can come in contact with transmitter surfaces. This can cause an increase in current flow in the entire circuit system. Installing a ground fault trip mechanism like an MCB helps regulate such mishaps by shutting out the power supply.

MCBs by Schneider Electric

The importance of MCBs cannot be contested. These small but powerful devices protect multiple devices in our homes and commercial spaces. With such multi-purposes utility, it’s essential that your MCB be of high quality and durability. Schneider Electric offers such MCBs in a wide range of types and sizes. The renowned electrical appliance brand offers the best MCBs in the market with added protection and guarantee of durability. So protect your devices with the best MCBs by Schneider Electric.

MCBs play a vital role in maintaining the safety and integrity of electrical systems. Their primary purpose is to protect circuits from damage caused by excessive current flow. This protection is critical in two main scenarios:

• Preventing Overloads: An overload is what happens when too many appliances draw current from a single circuit, exceeding its designed capacity. MCBs quickly trip and break the circuit, preventing overheating and potential electrical fires.
• Protecting Against Short Circuits: A short circuit occurs when a live wire comes into contact with a neutral or earth wire. This results in a sudden surge of current that can be extremely dangerous. MCBs instantly detect this surge and trip to isolate the faulty circuit, minimising the risk of electrical shocks or fire.

Compared to traditional fuse types, MCBs offer significant advantages in modern electrical installations. They are resettable, eliminating the need for replacements, and their compact design allows for more circuits to be protected in a smaller space.

MCBs are cleverly designed to respond to different types of electrical faults, using two main operating mechanisms:

• Thermal Operation: For overload protection, an MCB relies on a thermal bimetallic strip. When the current flowing through the MCB exceeds its rated value, the bimetallic strip heats up and bends due to thermal expansion. This bending action triggers a mechanism that trips the MCB, interrupting the current flow and protecting the circuit.
• Magnetic Operation: To handle short circuits, MCBs utilise an electromagnetic coil. When a short circuit occurs, a very high current flows through the coil, generating a strong magnetic field. This magnetic field forces a plunger to move, instantly tripping the breaker much faster than the thermal mechanism.
• Arc Extinguishing: When an MCB trips due to either overload or short circuit conditions, it can generate an electrical arc between contacts. To prevent this arc from causing damage, MCBs incorporate an arc chute. This chamber contains a series of metal plates that cool and split the arc, protecting the surrounding components.

Selecting the correct Miniature Circuit Breaker (MCB) is crucial for ensuring electrical safety and compliance with Australian standards. Here are the key factors to consider when determining what MCB is right for your application:

• Circuit Type and Load: Identify the type of circuit you need to protect (lighting, power, etc.) and the total current draw. This will determine the appropriate breaker rating.
• MCB Type (A, B, C, D): Consider the characteristics of the load. For sensitive electronics, Type A is suitable. For household circuits, Type B is common. Type C is better suited for inductive loads like motors, while Type D handles very high inrush currents.
• Number of Poles: Determine how many live conductors need to be protected. Single-pole MCBs are sufficient for most domestic circuits, while double-pole MCBs are necessary for appliances requiring greater isolation.
• Breaking Capacity: This indicates the maximum fault current the MCB can safely interrupt. It should be chosen based on the potential short-circuit current at the installation point, common ratings include 6kA or 10kA depending on application needs.

In Australia and New Zealand, electrical installations must comply with the AS/NZS : standard, also known as the "Wiring Rules." This standard outlines essential requirements for electrical safety, performance, and installation practices, ensuring that electrical systems are safe and reliable.

When choosing Miniature Circuit Breakers (MCBs), it's crucial to select those that meet the AS/NZS : standard. This ensures that the MCBs have been tested and certified to provide reliable protection against overcurrents and short circuits.

Key Compliance Aspects:

• Certification Marks: Always look for MCBs that carry appropriate certification marks indicating compliance with Australian standards. These marks ensure that the products have been tested for safety and performance.
• Residual Current Devices (RCDs): The AS/NZS : standard mandates the use of RCDs on all final sub-circuits in residential installations. Ensure your MCBs are compatible with RCDs to enhance protection against electric shock.
• Arc Fault Detection: While not a requirement, consider MCBs that incorporate arc fault detection capabilities. These devices can identify arcing conditions that may lead to electrical fires, providing an additional layer of safety.
• Installation Practices: Proper installation is critical for compliance. Ensure that MCBs are installed in accordance with the spacing and clearance requirements outlined in the standard, such as maintaining a minimum clearance of 1 metre around switchboards.
• Regulatory Oversight: Compliance is enforced by various regulatory bodies across states, including Energy Safe Victoria and the Queensland Electrical Safety Office. Familiarise yourself with local regulations to ensure full compliance.