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RCD vs. MCB: 7 Main Differences

RCD and circuit breaker in an electrical panel
RCD and circuit breaker in an electrical panel

What is the difference between RCD vs. MCB? If you are looking for the answer, you have come to the right place. Here, we will explain the RCD and circuit breaker differences, their working and functions, and some applications of each device, starting with the definitions.

RCD and Circuit Breaker

When it comes to electrical system safety, two devices play a very important role: the RCD (Residual Current Device) and the circuit breaker. We will have a look at the main differences between an RCD and a circuit breaker so that you can understand when to use each one.

But before that, how about a quick recap on what each device means? After the RCD and circuit breaker definition, we dive into the main difference between these devices. This way, it will be easier for you to understand when each one is used.

RCD Definition

The residual current device, RCD, is an electrical safety device that disconnects the power supply if it detects an imbalance between the current flowing into and out of an electrical circuit.

The main function of the RCD is to protect people from electric shocks. It does this by disconnecting the power supply when it detects that the current flowing through a circuit is not balanced.

This often happens if someone touches a live wire with their bare hands. The current flowing through the person’s body will reduce the current flowing through the wire, and this would cause an imbalance.

The RCD would then disconnect the power supply to prevent the person from being electrocuted, typically within a few milliseconds. In addition to preventing electric shocks, RCDs can also help to prevent fires by disconnecting the power supply if they detect a fault.

MCB Definition

The miniature circuit breaker, on the other hand, is designed to protect the electrical circuit from damage due to overcurrent situations. Overcurrents are common in many electrical circuits, both high and low voltage.

An overcurrent can occur, for example, if there is a short circuit or if too much current is drawn through the circuit (such as might happen if an appliance suddenly stopped working and started drawing more current than usual).

The breaker will trip (or disconnect the circuit), stopping the flow of current and preventing the circuit from being overloaded. A circuit breaker does not protect against electric shocks as RCDs do, but it does protect against fires caused by overloading a circuit.

RCD vs. MCB in a consumer unit
RCD vs. MCB in a consumer unit

RCD vs. MCB

When choosing which device to use, it is important to consider the different features of each one. So, to summarize, the main differences between RCD vs. MCB, are given below: We divided the differences based on various factors such as function, working, application, and so on.

RCD vs. MCB: Function

One main difference between RCD and circuit breakers is the type of protection that each device offers. The RCD offers protection against electric shock, by disconnecting the circuit when it detects a current leakage to earth.

The miniature circuit breaker offers protection against overcurrent by disconnecting the circuit when the current flowing through it exceeds a certain level. These devices are rated differently for different circuits and electrical systems.

RCD vs. MCB: Working Principle

Another difference between RCD and circuit breaker is the working principle on which each device operates. The residual current device operation is based on the difference in the current flowing through the live and neutral wires generating a magnetic field.

The miniature circuit breaker, on the other hand, works by sensing the current flowing through the circuit. When the current flowing through the circuit exceeds a certain level, it trips (or disconnects the circuit).

RCD vs. MCB: Test Button

One way to test RCD devices is by pressing the test button. This will cause the RCD to trip (or disconnect the circuit). The RCD test button is clearly visible on the front of the device.

There is no such test button on a miniature circuit breaker. Instead, MCB circuit breakers have a different way to test whether the mechanism is working properly.

RCD vs. MCB: Location

Another difference between RCD vs. MCB is the location at which each device is typically installed. RCDs are usually installed downstream of the main circuit breaker (or fuse), in order to protect against electric shock.

Circuit Breakers are usually installed upstream of the RCD. In other words, a circuit breaker provides protection to even the RCD itself.

RCD vs. MCB: Applications

Circuit breakers find use in a broad range of applications, from domestic to commercial and industrial. RCD use is also wide and varied depending on the type and level of protection required.

However, residual current devices are more commonly used in homes where they offer protection against electric shock. They are also often used in commercial places to protect people from fatal electrical accidents resulting from electrocution.

RCD vs. MCB: Ratings

It is also important to consider the ratings of RCDs and circuit breakers, as they are different for different applications. Breaker and RCD ratings indicate the maximum current that each device can handle before the trip (or disconnection).

RCDs are typically rated between 16A to 125A. Miniature circuit breakers, on the other hand, are built to handle currents from as low as 0.5A to as high as 125A.

RCD vs. MCB: Types

There are 5 main types of RCDs: type AC for alternating current, and type A for both alternating and pulsating direct fault currents. Others include type B RCD, type F, and S types which are used for both alternating and direct fault currents.

Miniature circuit breakers are also classified as types A, B, C, D, K, and Z but based on their trip characteristics. The most common types used in households are B and D, while the other classes are mostly used in light commercial and industrial applications.

Conclusion

Both RCDs and circuit breakers offer protection against overcurrent, but they differ in terms of working principle, location, applications, and other aspects. It is important, therefore, for electricians to choose the right device for the job, based on the specific needs of the application.

Generally, circuit breakers offer protection against instances of high current and circuit overload, while RCDs offer protection against electric shock caused by fault currents.

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William

I am William, Electrical Engineering Author. Dedicated to writing technical articles on Timer Relay, Monitoring Relay, Surge Protection Device and other electrical devices. With 7 years of writing experience, I am committed to providing accurate and in-depth expertise to my readers.

1 comment

    Hallo William,
    Ik ben vandaag voor een storing gebeld. Bij de klant bleek kortsluiting te zijn geweest in een groep. Deze was beveiligt met een MCB/RCD (Aardlekautomaat) B16 0,03A. Deze was na de sluiting afgegaan maar het bleek dat de hoofdzekering van D 25A Traag ook af was gegaan. Nou kan het een druppel zijn geweest en dat de D 25A al meerdere keren was blootgesteld aan kortsluitstromen maar ik vind het toch vreemd. Ik kan over deze specifieke Aardlekautomaat ook niks vinden op het internet. Heb je enig idee wat het zou kunnen zijn? Het type aardlekautomaat is Hager AD 037G. Ik hoor graag wat je er van denkt.

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