How does a miniature circuit breaker actually work?

Miniature circuit breakers (MCBs) ensure electrical safety in homes, offices, and other buildings as well as for industrial applications by protecting electrical installations against overloads and short circuits. Once a fault is detected, the miniature circuit breaker automatically switches off the electrical circuit to prevent damage to wires and to avoid the risk of fire. Warranting reliability and safety for people and assets, MCBs are equipped with two tripping mechanisms: the delayed thermal tripping mechanism for overload protection and the magnetic tripping mechanism for short circuit protection.

Just imagine you live in an apartment built maybe sometime in the 60s. You’ve just decided to get your annual spring clean over and done within record time tonight. In preparation, you’ve compiled your favorite MP3 playlist on your PC and it’s being streamed in all rooms. You’ve filled the dishwasher and turned it on, the washing machine is full of clothes and you’ve flicked the switch, you’ve pulled the vacuum cleaner out of its corner and plugged it in.

Not long after, you hear a quiet ‘CLICK’ from the corner (or, in the case of older apartments, from out in the hallway). The lights are out, the music is only playing in a couple of rooms or not at all, the washing machine and the dishwasher are off and the vacuum cleaner has fallen silent.

You’re annoyed, and you try to figure out what’s going on. Usually, ‘the cause’ can be located quite quickly: that ‘thing’ in the box on the wall is off. So, you switch it back on, and off you go. Moments later, the circuit breaker once again clicks to cut off the overload. In a pinch, you might even get the bright idea that you might be able to jam the switch in the ON position so that you can just finish vacuuming your apartment.

What happened?

Annoyingly, doing that won’t let you effectively clean your apartment nowadays. Our ABB miniature circuit breaker will, thankfully, protect your wires from both overloads and short-circuits even if the switch has been forced into the ON position, due to what we call a ‘trip-free’ MCB. Even if your finger keeps the switch in the on position, the internal mechanism will trip and ensure safe disconnection of the overloaded circuit.

What exactly does an MCB do?

The short answer: it protects wires from overloads and short-circuits. When we look on the inside of an MCB we can see how that actually works.

While electricity has become an indispensable component of our lives, the fact is, it comes with its own hazards to human life and property. Electrocution and fire being the two major risks associated with electricity, one cannot afford to be negligent when it comes to insulating equipment.
A Residual Current Circuit Breaker (RCCB) is an important safety measure when it comes to protection of electrical circuits. It is a current sensing device, which can automatically measure and disconnect the circuit whenever a fault occurs in the connected circuit or the current exceeds the rated sensitivity.

Principle behind RCCB

RCCB works on the principle of Kirchhoff’s law, which states that the incoming current must be equal to the outgoing current in a circuit. RCCB thus compares the difference in current values between live and neutral wires. Ideally, the current flowing to the circuit from the live wire should be the same as that flowing through the neutral wire. In case of a fault, the current from the neutral wire is reduced, the differential between the two known as Residual Current. On spotting a Residual Current, the RCCB is triggered to trip off the circuit.

A test circuit included with the Residual Current device ensures that the reliability of RCCB is tested. When the test button is pushed, the current starts to flow through the test circuit. As it creates an imbalance on the neutral coil of the device, the RCCB trips and supply is disconnected thereby checking RCCB’s reliability.

Benefits of RCCB

Provides protection against earth fault as well as any leakage current

Automatically disconnects the circuit when the rated sensitivity is exceeded

Offers possibility of dual termination both for cable and busbar connections

Offers protection against voltage fluctuation as it includes a filtering device that guards against transient voltage levels.

Moulded Case Circuit Breaker is an electromechanical device which protects a circuit from overcurrent and short circuit. It provides overcurrent and short circuit protection for circuits ranging from 63 Amps up to 3000 Amps.

The primary function of an MCCB is to provide a means to manually open a circuit and automatically open a circuit under overload or short circuit conditions. The overcurrent, in an electrical circuit, may result from short circuit, overload or faulty design.

It is generally installed on the secondary side of transformer stations (main switch or for protecting individual branches). In industry, we can use it in switchgear or for protecting the motors as well we have big requirements in shipbuilding. For building applications, you can find it as the main protection switch.

The Molded Case Circuit Breaker is a specific type of circuit breaker.

NEMA defines Molded Case Circuit Breaker as devices designed to open or close a circuit by nonautomatic means and to open the circuit automatically on a predetermined overcurrent without damage to itself when properly applied within its rating.

The term “molded case” simply refers to the construction of the circuit breaker and refers to the fact that the circuit breaker is an assembled unit in a supporting housing of insulating material.

MCCB vs Fuse

MCCB is an alternative to a fuse since it does not require replacement once an overload is detected.

Unlike a fuse, an MCCB can be easily reset after a fault and offers improved operational safety and convenience without incurring the operating cost.

What are circuit breakers?

Essentially, circuit breaker is lockdowns but for a limited amount of time. They are designed to break the chain of infection, and bring the infection rate down. It’s hoped that circuit breakers will help to reduce pressure on health services as hospitalizations due to Covid-19 rise.

This is crucial for the U.K., which has the third-highest number of coronavirus cases in Europe, with its tally now standing at just over 744,000 cases with 43,816 fatalities, according to data from Johns Hopkins University. It is currently battling a dramatic second wave of infections, like the rest of Europe, particularly in northern England.

On Monday, 18,804 new daily infections were reported, up from 16,982 on Sunday. The seven-day average number of cases on Oct. 16 was 17,649, according to government data, compared to 14,588 a week before.

Scientists advising the government seem to favor circuit breakers, as does the opposition Labour Party, with both encouraging the government to implement a mini-lockdown.

While technology has improved over years, the primary means of controlling electrical circuits remain the same. Among these are contactors , and this article examines the different types of contactors and how they work. It also looks at the differences between contactor and relay , AC contactor and DC contactor.

What Is a Contactor?

A contactor is an electromechanical switch whose function is to make or break the connection between the power supply and the load. The contactor is electrically controlled and usually powered at a much lower level than the switched circuit. For example, you would have a 24-volt coil electromagnet that controls a 230-volt motor switch.

A contactor’s applications include controlling electric motors, thermal evaporators, lighting, capacitor banks , heating, and other electrical loads. Contactors range in size and capacity. You have those that you can easily lift with your hand to massive ones measuring about a meter on the side. You also have those with a breaking current ranging from a few amperes to thousands of amperes and those from 24V DC to many kilo volts.

Types of Contactors

Knife Blade Switch

It is the oldest type of contactors and uses ON and OFF electric motors. The knife blade switch consisted of a strip and a lever. The lever serves to pull the metal strip up and down, making this contactor a manual operation. It has several shortcomings which led to its discontinued use. These challenges include

High incidences of arcing led to a short life span for the contactor

Had safety risks

Was vulnerable to moisture and dirt

Double Break

Manual Contactor

This contactor was a replacement and improvement on the knife blade switch. It, however, still features manual operation. Other key features are

Double break contacts, which can open the circuit in two places simultaneously, providing more current in smaller spaces.

Properly enclosed unit protecting the inner parts

Safer operation

Smaller size

Magnetic Contactor

This is the latest contactor design and is the most advanced of them all. It is commonly used in industrial applications due to its features like

It works automatically

Offers the safest operation

Uses the least amount of control current to open and close a circuit.

How Does a Contactor Device Work?

To understand the contactor working, you need to know the various parts of a contactor. There are three essential components of a contactor;

The coil/electromagnet


The frame or enclosure

Coil or electromagnet

The coil provides the driving force in a contactor that closes the contacts. It features a coil wound around an electromagnetic core and thus behaves like an electromagnet. The coil has two parts, a fixed one and a movable part with a spring connecting both parts. This structure creates a spring return mechanism.

A rod called an armature is connected to the movable part. When the coil’s force is more than the spring’s force, both contacts connect. When the spring’s force is more than the coil’s force, the contacts disconnect.

The input of the contactor coil could either be AC or DC. This current comes from an external control circuit for the contactor and serves to excite the electromagnetic core. For AC magnetic contactor, soft laminated iron is the electromagnetic core material. It helps reduce the eddy current loss. In DC contactors, solid steel is the material for the electromagnetic core as the issue of eddy current does not arise.

Magnetic Starter

Magnetic starters are the most common type of starter & they are mostly used for high power AC motors. These starters operate electromagnetically like a relay that breaks or makes the contacts using magnetism.

It provides a lower & safer voltage for starting & also includes protection against low voltage & overcurrent. During the power failure, the magnetic starter automatically breaks the circuit. Unlike manual starters, it includes automatic & remote operation that excludes the operator.

The magnetic starter consists of two circuits;

Power circuit; this circuit is responsible for supplying power to the motor. It consists of electrical contacts that turn ON/OFF the power supplied from the supply line to the motor through overload relay.

Control circuit; this circuit controls the contacts of the power circuit to either make or break the power supply to the motor. The electromagnetic coil energizes or de-energizes to pull or push the electrical contacts. Thus providing a remote control for the magnetic starter.

A overload thermal relay works on the heat produced by the excessive overload current. The heat produced by the overload current is utilized to trip the motor circuit. These are mostly used for protection of low-voltage squirrel cage induction motors or DC motors of lower output rating. As a professional manufacturer, we will continue to provide customers with excellent quality products.

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