Molded case circuit breaker and its applications!

Do you know what a molded case circuit breaker is, do you know what it is for and what are its applications within electrical installations, what is its importance and the main differences and types of molded case circuit breakers? If your answer is no or if you have any questions on the subject, come with us to learn a little more.

What is a molded case circuit breaker?

Molded case circuit breakers were developed for the protection of distribution circuits, generators and motors, they can be found in different types of currents between 16A to 1800A. The name mold box breaker is due to the type of armored assembly of the circuit breaker, they are assembled in pre-molded thermoplastic boxes, these compact boxes form the outer housing of the circuit breaker usually the outer part has two parts.

The molded case circuit breakers are developed in compliance with the NBR60947 standard, which deals with low voltage control and maneuvering devices, their internal components and contacts are robust, the arc extinguishing chambers are capable of interrupting the circuit with currents from 20X to 30X more than ordinary circuit breakers.

The main feature of molded case circuit breakers is their robustness, as the breaking capacity of the circuit under load is much higher compared to ordinary circuit breakers. A common feature of these circuit breakers is the thermal and magnetic protection which in many models can be adjusted between 5x the rated current of the circuit breaker up to 10x the rated current, this setting is very important for industrial electrical circuits as it allows a more sensitive adjustment for more efficient protection the circuit.

Molded case circuit breakers of various models and manufacturers

Applications for the molded case circuit breaker.

Molded case circuit breakers are mainly applied in industrial environments, where interruptions with high short circuit current are required, we can also find them in QDC (compact distribution board) and QGBT (general low voltage board) of commercial establishments and condominiums.

Molded case circuit breakers are also applied to protect electric motors because they have built-in magnetic protection, the magnetic trip (trip by magnetic protection) can be adjusted up to 12X the rated current of the circuit breaker, therefore, it is possible to avoid the circuit breaker trip at the motor start where high starting current occurs, this type of adjustment aims to protect the motor in short-circuit currents.

Another application of the molded case circuit breaker is the protection of generator circuits since the circuit breaker has thermal and magnetic tripping, the magnetic tripping can be adjusted according to the rated current of the circuit breaker, the adjustment can reach up to five times the nominal, This way, there is effective protection in case of short circuits of circuits supplied by the generator.

We can also point out that molded case circuit breakers can be used to be circuit breakers or disconnectors, as they are developed to perform electrical maneuvers, also acting without triggering thermal or magnetic protections, in addition to having double insulation for the protection of users. installed with locking handles that allow the equipment to be consigned in accordance with the NR10 regulatory standard.

Difference between molded case circuit breaker and other circuit breakers

Molded case circuit breakers compared to ordinary residential circuit breakers

The most common circuit breakers on the market are mini circuit breakers , they are applied mainly in residential electrical installations, these circuit breakers in case of high short-circuit currents, generally, currents above 5KA, when they interrupt the current flow, they do not support the magnetic thermal effect, this effect is so intense that the internal components do not support the heat and the electric arc caused by the interruption of the electric current, therefore, the internal contact structure of the components is damaged or often generates a short between phases (phase -phase) inside the circuit breaker itself causing an explosion.

In the case of molded case circuit breakers, the supported short-circuit currents are much higher, due to the robustness of the circuit breaker, it supports a high intensity of magnetic thermal effect, which allows them to interrupt the passage of high short-circuit currents. -circuit. As the molded case circuit breakers were designed for this, they have a robust arc-extinguishing chamber, capable of withstanding the thermal effect at the moment of opening, this design allows its components not to be damaged.

The most important data when choosing a molded case circuit breaker is undoubtedly the data known as ICU and ICS, the origin of this data is related to the tests carried out on circuit breakers according to IEC 60947-2 – Control devices and low voltage maneuver.

Observe the mathematical calculation for dimensioning the general protection circuit breaker, the result found must be consistent with the ICU informed by the circuit breaker manufacturer:

Mathematical model for calculating the general circuit current

ICU – Rated ultimate short-circuit breaking capacity

Basically this data means the maximum breaking capacity of a short-circuit current, that is, in the event of a short circuit, this is the maximum current supported by the circuit breaker after a certain sequence of tests. It is important to note that after this test, it is not guaranteed that it will be able to conduct its rated current described, however it must be safe in this condition during and after the interruption of a short circuit current and for this proof it is also subjected to an electrical insulation test after the ICU test. Generally, the ICU value is found in the circuit breaker manufacturer’s catalog and is widely used to specify which circuit breaker to use in the project.

ICS – Rated service short-circuit breaking capacity

This data is the maximum capacity of interruption of a short-circuit current supported by the circuit breaker after a certain sequence of tests, the difference of this data for the previous one is that after the sequence of tests the circuit breaker needs to be, in operation voltage, able to conduct and withstand its rated current, operating normally. The circuit breaker must preserve this characteristic of conducting the ICS current when there are up to a minimum of 3 short circuit events, returning to operate in an integral manner after those occurred.

The interruption capacity of the ICS current can be found in the manufacturers’ catalogs as a percentage of the ICU, the typical values ​​are 25%, 50%, 75% and 100% of the ICU.

We provide an excellent video that deals with box molding circuit breakers, we hope that your doubts are solved and that you can understand for which applications we should use this type of circuit breakers, this video is also recommended so that you can go deeper into the concepts of current ICU and ICS , to better understand the difference between these data presented by the circuit breaker manufacturer.