What is a Molded Case Circuit Breaker?

Source GSES

Molded case circuit breakers are used to protect electrical equipment from serious damage due to short-circuit or overload conditions. In these circuit breakers, a metal case is molded around and firmly secures various inner parts like an operating mechanism, terminals, and auxiliary contacts. An ordinary circuit breaker has a switch with movable contacts that operate in response to excess voltage.

When the current flowing through the circuit exceeds a safe limit, the movable contacts move to interrupt the current flow. A molded case circuit breaker is equipped with a compressed spring mechanism that holds multiple contact points within a single compact casing. It significantly reduces the likelihood of arcing and makes maintenance operations easier.

A Molded Case Circuit Breaker is essentially a package of multiple contact assemblies used for switching high voltages or currents in an electrical system. There are several variations of this device depending on its purpose within the system; however, all operate using a common principle.

How Does a Molded Case Circuit Breaker Work?

Source Electrical Technology

Molded case circuit breakers depend on the thermal-magnetic (electromechanicaL) trip units to operate.  These trip units are typically a pair of contacts enclosed in a sealed glass envelope filled with an inert gas. The purpose of this envelope is to contain the ignitor, which is used to heat up the magnetic coils. When a current overloads the circuit, it heats up the magnetic coils until they become hot enough to trigger the thermal-magnetic trip unit. The trip unit then pulls two sets of contacts apart, physically opening the circuit and preventing any damage from occurring.

The thermal-magnetic trip unit relies on several different components to operate correctly and safely in an electrical system:

– The thermal element is the small piece of metal that heats up when current flows through it.

– The magnetic coil is the large iron core that wraps around the thermal element.

– The ignitor is a piece of tungsten wire located inside a sealed glass tube. The ignitor is used to heat up the magnetic coil until it becomes hot enough to complete the circuit and trip the breaker.

– The thermal resistors are wires in series with the thermal elements and are used to measure the temperature change of the element over time. They can be used in conjunction with a thermocouple, which allows for an exact measurement of temperature change over time, or a resistance thermometer, which measures resistance change over time.

– The electrical contacts are made out of silver or silver alloy and serve as conductors for electricity flowing into or out of an electrical system.

Why Install Molded Case Circuit Breakers?

There are multiple reasons to install a molded case breaker in your electrical system. These circuit breakers protect against overcurrent, short circuit, and ground fault. They are also designed to trip at a lower current threshold to protect against higher currents caused by serious issues like insulation failure or faulty wiring.

MCCBs are generally used in high-voltage or high-current systems, such as in an industrial facility or on a power grid. They are the most common type of circuit breakers used because they are highly reliable, safe, and easy to use.

MCCBs are made from a material that is resistant to corrosion and other environmental factors, making it ideal for use in wet environments like chemical factories or marine vessels. Circuit breakers are essential for protecting machinery from getting damaged and/or shutting down.

What are the main features of MCCB?

When buying MCCBs, you will notice that they come with different specifications which include:

-Ue: This is the rated operational voltage. It is the voltage at which the MCCB will trip.

-Icu: This is the maximum current rating of the MCCB. It is measured in amperes and should not exceed the maximum current carrying capacity of the circuit wiring.

-Trip class : The trip class indicates the sensitivity of a circuit breaker to short circuits. The lower the number, the more sensitive it is.

-Earth leakage protection: This feature ensures that any fault current flowing through an earth conductor will be interrupted by a sensitive magnetic trip system, preventing shock hazards caused by leakage currents and/or faulty equipment.

-Degree of protection (DOP): The degree of protection indicates how much energy can be dissipated by a circuit breaker before it trips or breaks down. This is measured in kA2s, with higher numbers indicating greater resistance to fault currents and greater protection for equipment connected to it.

-Uimp: Impulse withstand voltage-this is the voltage at which the MCCB is deemed to have passed a test for short circuit protection. This is measured in kilovolts (kV).

What is MCCB breaking capacity?

The breaking capacity of a circuit breaker is the maximum power it can break in a short-circuit situation. It is measured in amperes and kilovolt-amperes (kVA).

The breaker capacity must be greater than the maximum load expected on the circuit. A 20-amp circuit breaker can handle up to 20-amps of current. If you put more current through the circuit, the breaker will open the circuit to prevent electrical damage.

The same applies if you have an appliance with a lower current requirement than the circuit breaker’s capacity. In this case, the breaker won’t open the circuit when the appliance is turned on.

The circuit breaker capacity is often indicated by a letter code, such as ‘E’ for 15, 20, or 30 amps; ‘G’ for 10 or 15 amps; ‘H’ for 20 or 30 amps; ‘J’ for 15, 20, or 30 amps; or ‘K’ for 10 or 20 amps.

Key Differences Between MCCBs and DCBs

Now that we know what MCCB is, lets give you a brief overview of DCB. DCB stands for Double-Contact Block. A DCB is similar to an MCCB, but it has two separate contacts for each phase instead of four. It is designed for use with three-phase systems and requires at least three wires (two wires per phase).

MCCBs are generally used in residential, commercial, and industrial applications. They are also used in high-voltage applications (600V and above) because they require less space than a DCB. MCCBs are rated up to 600V, while DCBs are typically rated up to 250V.

MCCBs have a three-pin design that is easy to install and maintain. However, they’re more expensive than an equivalent DCB.

DCBs offer greater protection against arc faults than MCCBs do. In addition, they have a greater number of protection features for each phase compared to an MCCB.

DCBs can be installed with or without the use of a neutral conductor at the load end of the circuit; however, this is not possible with an MCCB. 

How do you reset a molded case breaker that has been tripped?

You should check the circuit breaker’s rating before resetting it. For example, if the breaker rating is 20A, the reset button should be held for a minimum of 20 seconds before it can be reset.

If the breaker rating is 10A, it should be pressed for 10 seconds before it can be reset. You can also use a circuit breaker resetting tool to reset the circuit breaker. If the circuit breaker is tripped due to a ground fault, you can reset it by removing the ground fault.

What is the difference between an air circuit breaker and molded case circuit breaker?

Air circuit breakers are designed to handle 10 to 600 amps and are used in low-voltage electrical systems. MCCBs are used in high-voltage electrical systems with voltages exceeding 600 volts.

Air circuit breakers are less expensive than molded case breakers, and they can be installed in a variety of electrical systems. Air circuit breakers are smaller in size than molded case breakers, making them suitable for compact spaces.

Air circuit breakers can trip when there is an overload or a short circuit, whereas molded case breakers are triggered by ground faults.

Where to install model case circuit breaker？

MCCBs are suitable for indoor and outdoor use. You can install these circuit breakers in an industrial facility, chemical factory, data center, marine vessel, or in any other high-voltage or high-current system.

Where to install model case circuit breaker? You can install MCCBs in the following places: Industrial plants, data centers, or any other electrical system that operates at high voltages.

Marine vessels or ships that require electrical protection against faults in the power supply. Hospitals and other healthcare facilities that need industrial-grade electrical equipment.

Where to buy model case circuit breaker

You can buy MCCBs from electrical distributors. The best places to buy these circuit breakers are online stores. When you buy a MCCB, make sure you get the correct rating of the circuit breaker.

If you want to import molded case circuit breakers in China, then it will be better to go through a sourcing agent. This way, you will be sure of getting a reliable manufacturer or even supplier.

ICRFQ is just one of the trusted sourcing agents that will help you get quality MCCBs that will meet your application needs. We have been in the business for more than 20 years. We have a wide network of reliable manufacturers from different countries.

Wrapping up

I hope you have learned all the essentials of molded case circuit breakers. You can now buy one or even wholesale if you are in the electrical component business. However, don’t forget to get these devices from reputable suppliers and manufacturers.

If you want to find more Electronic Components Distributors, please check out the following articles:

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