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Molded Case Circuit Breaker and Working Explained

Molded case circuit breakers
Molded case circuit breakers
Resource: https://www.designworldonline.com

A molded case circuit breaker is a very common (and crucial) electrical protection device. The aim of this article is to provide an introduction to the basics of these breakers, how they work and where to use them. Here is what it covers: molded case circuit breaker meaning, operating mechanism, working, cost, and use.

What is a Molded Case Circuit Breaker?

A molded case circuit breaker is simply an electrical protection device – a type of circuit breaker that’s meant to interrupt higher currents than the miniature circuit breaker, with capacities of up to 1100V for voltage and 2500A or even higher current protection.

It’s also called an MCCB, which is the abbreviation for molded case circuit breaker. Here’s why they call it so as well as how it appears in electrical drawings:

Molded Case Circuit Breaker Meaning

The term “molded case” refers to the plastic casing that encloses the breaker. The casing serves to protect the breaker by keeping away external elements as well as offering thermal and mechanical protection.

More importantly, the molded case breaker housing provides the much-needed insulation for safety, given that the breaker operates in higher voltage and higher current situations than the regular MCB.

Molded Case Circuit Breaker Symbol

In electrical diagrams, a molded case circuit breaker is represented with a specific symbol for easier identification, just as any other electrical component.

Usually, the molded case circuit breaker symbol is a small curved line with two dots and straight lines on either side of the curve, as shown in the picture above. This symbol represents the breaker’s switching action.

Molded case circuit breaker diagram to show internal components
Molded case circuit breaker diagram to show internal components
Resource: https://www.youtube.com/watch?v=uUgGlwStbtw

Parts of Molded Case Circuit Breaker

In order to understand the MCCB circuit breaker better, it’s crucial that examine its parts and how they help the device perform its intended functions. The main MCCB components are listed below:

  • Molded Case: This is the outer shell of the MCCB, which encloses all of the other components and protects them from external damage. The circuit breaker molded case also provides insulation.
  • Load and Line Terminals: MCCB terminals are the primary connection points for attaching conductors. The upper terminals connect to the load, while the lower terminals connect to the line side.
  • Contacts: The contacts are generally made of a silver alloy. They provide the necessary connection between the load and line sides of the circuit breaker. They also open and close when the breaker trips.
  • Operating mechanism: This is composed of various parts. The molded case circuit breaker operating mechanism is responsible for opening and closing the contacts when required.
  • Trip Unit: The MCCB trip unit is component that senses an overload or a fault in the circuit and activates the operating mechanism to open the contacts.
  • Handle: The MCCB handle is the user’s interface with the breaker. It can be used to manually open or close the contacts, as well as to reset a tripped circuit breaker when necessary.
  • Arc Chute: When the breaker contacts open, an arc is created. The arc chute directs the arc away from the contacts, reducing arcing and resulting in a safer operation.

Molded Case Circuit Breaker Function

Molded case circuit breakers are primarily designed to protect electrical systems and equipment from overloads, short circuits, and other potentially damaging conditions.

They do this by automatically disconnecting the circuit when it detects an overcurrent or fault in the system. Essentially, the protective function of a molded case circuit breaker includes the following:

  • To protect the electrical circuit from overloads that may cause damage to it
  • To protect the equipment connected to the circuit from damage due to excessive current flows
  • To minimize disruption of service during a fault or overload condition such as motor inrush current
  • To provide a means of manually resetting the electrical circuit when it has been disconnected due to an overcurrent or fault condition
  • To disconnect the circuit during an emergency situation, or when a part of the system needs to be shut down for maintenance or other reasons
Cut away image to show the internal construction of MCCB
Cut away image to show the internal construction of MCCB
Resource: https://www.youtube.com/watch?v=98Qjkx7D-rA

Molded Case Circuit Breaker Working Principle

The molded case circuit breaker working principle is typically based on a thermal or magnetic trip mechanism. Most often, it’s a combination of both. This is what gives the commonly called thermal-magnetic molded case circuit breaker its name.

Here is how a thermal magnetic MCCB works to protect your electrical system or equipment: Note that the magnetic part provides protection against short circuit faults, while the thermal part detects overcurrents.

MCCB Thermal Magnetic Trip

Thermal MCCB tripping provides an intentional delay before the breaker can trip. This accommodates short-lived faults such as the inrush currents, which would otherwise cause nuisance trips. It relies on a bimetallic mechanism which, when heated by an overcurrent, bends to disconnect the circuit.

The magnetic mechanism is primarily a solenoid and meant to provide an instantaneous (or almost instantaneous) trip for more serious faults like short circuits. In an overcurrent, the magnetic force builds quickly, triggering the tripping mechanism and disconnecting the circuit.

MCCB Electronic Trip Unit

This molded case circuit breaker operating mechanism comprises an electronic module, semiconductor devices and other parts. The module contains software to electronically measure the current flowing through the breaker conductors.

Upon sensing a sudden increase and based on the set values, the module will activate the tripping mechanism. This allows for excellent adjustability.

Molded case circuit breaker use in an electrical system
Molded case circuit breaker use in an electrical system
Resource: https://www.youtube.com/watch?v=VFhPjU6ZQvA

Molded case circuit breaker uses

Molded case circuit breaker uses include various industrial and household applications for safety and reliability. The most common application is for circuit protection in residential, commercial, and industrial areas.

Molded case breakers are used to protect motors from overloads and short circuits in factories and other settings. They also help protect sensitive electronic equipment from damage due to voltage spikes or surges.

Other applications include protecting critical systems, such as medical equipment and emergency lighting. They provide a higher level of safety than regular MCB or miniature circuit breaker, ensuring that power is quickly shut down when it’s needed most.

Molded Case Circuit Breaker Price

How much is an MCCB? The molded case circuit breaker price can vary widely. A lot depends on its size, features, and application but generally, the larger the MCCB, the higher its cost.

With the many different molded case circuit breaker sizes out there, therefore, pricing can range from $200 to $500 and higher. It always pays to shop around for the best value and look for trusted brands that offer high-quality parts and warranties.

Only remember that, as with most equipment, you get what you pay for in terms of features and quality; more expensive MCCBs tend to have more features and better reliability than lower-priced options

Conclusion

In summary, molded case circuit breakers are crucial protection devices in many electrical systems. They provide protection against overloads, short circuits, and other fault conditions, ensuring that your equipment is safe from damage or disruption.

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