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MCB and how much load they can handle and the different types of circuit breaker

Published by Lee Kelly on 13 October 2021

Different Types of MCB: How Much Load Can an MCB Handle?

An MCB is a critical component of a circuit. It increases safety and reliability and protects the longevity of instruments and equipment connected to the circuit. Read on to discover more about the different types of MCB and their respective load limits.

What Does an MCB Do?

MCB stands for miniature circuit breaker. This component protects electrical circuits against power overloads, short circuits and overheating by breaking the electrical connection and halting the flow of electricity.

Critical Power Supplies - A range of different MCB's laid out on a table.

How Does the MCB Protect Electrical Circuits and Components?

The MCB works on the concept of planned failure. When a current passes through the MCB's constituent bimetal part, the temperature of the bimetal increases. Once the temperature of the bimetal exceeds its designed maximum level, the breaker mechanism is tripped and the flow of electricity ceases.

This protects sensitive circuit components that may become damaged when the current load becomes too great (current trip) or when the temperature within the circuit exceeds safe levels (thermal trip). It also prevents overheating in cabling, which occurs when the current is too high.

Another constituent part of the MCB is its electromagnetic coil. If short-circuiting occurs, the increased current through this coil creates a magnetic field that also triggers the breaking mechanism via a plunger built into the MCB. This electromagnet plunger provides instantaneous circuit breaker tripping according to the BSEN60898-1 standard.

Whether a short circuit or a power overload is taking place, the MCB's built-in arc chamber mitigates the damage that would otherwise be caused by the resulting electrical arc.

Different Types of MCB

The main types of MCB are determined according to their relative levels of sensitivity.

  • Type B

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Type B is the most sensitive of the domestically deployed MCBs. It is designed to trip if it experiences a current flow between three and five times that of the recommended upper level. More sensitive MCBs are available, such as the Type Z breaker, but these are not usually deployed in domestic settings.

  • Type C

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Type C is another common form of MCB. It is less sensitive than its Type B counterpart. Circuits serving small electric motors or fluorescent light fittings often use Type C circuit breakers, and the circuit will be broken when the current goes beyond five to ten times the rated load.

  • Type D

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Type D MCBs are less sensitive than both the Type B and C components. As a result, they are commonly deployed in circuits where high levels of current surge are not uncommon to prevent unnecessary power outages. The circuit breaker mechanism will trip when the current reaches between ten and twenty times the rated level. Larger motors are often used in conjunction with Type D MCBs, as are x-ray machines and welding systems.

  • Type K

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Type K MCBs sit between Types C and D, and are often deployed in motor circuits. With this type of MCB, the circuit will be broken when the current is between eight to twelve times the recommended upper level.

  • Type Z

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We've already touched on Type Z MCBs, and these are the most sensitive circuit breakers that are widely available on the market. Type Z components will cause the circuit to break when the current is at double or triple the highest recommended level. They are not commonly deployed in domestic settings and are generally used for sensitive applications where short-circuiting is a real danger, for example, circuits serving semi-conductors.

Selecting the Right MCB for Your Circuit

Choosing the right MCB is an important consideration. The information presented here is designed to give you a rough guide on which MCB is best for your specific application. The choice of MCB should come from the UPS or from the generator manufacturer, based on the specifications of the circuit and network components.