Open circuit breaker and molded case, do you know?

One thing that every professional in the world of electrical should think is that even though the laws of electrical are the same for many situations, the components can be different according to various characteristics such as circuit breakers for example. In this article we will show the main characteristics and differences between low voltage circuit breakers.

What is a circuit breaker?

The circuit breaker is an electromechanical protection device that has the function of protecting electrical installations, automatically disarming as soon as it identifies an electrical current that exceeds the nominal value of the electrical current of the circuit breaker, preventing the supply of energy to the circuit loads, preventing the loads and the circuit are damaged.

The circuit breaker can also be defined as an automatic trip switch that protects the electrical circuits of the installations, disarming as soon as it identifies short-circuit or overload currents, being essential to prevent accidents and even fires.

Circuit Breaker Models

There are basically three models of circuit breakers for low voltage, the mini circuit breaker , the molded case circuit breaker and the open circuit breaker. It is not just the mini circuit breakers that we have at home that are for low voltage. The open circuit breaker is also a low voltage circuit breaker, however it is much larger.

Naturally the larger circuit breakers carry more electrical current, but regardless of the electrical current that the circuit breakers conduct, other electrical phenomena that differentiate them is the ability to interrupt a short circuit, for example, the mini circuit breaker has the ability to interrupt a short circuit that arrives at 15,000 amps, in open circuit breakers this current can reach up to 150,000 amps, with open circuit breakers that can weigh more than 100 kg.

In addition to open circuit breakers and mini circuit breakers, there are still molded case circuit breakers. Molded case circuit breakers are between mini circuit breakers and open circuit breakers, both in current value and in size.


Open circuit breakers and molded case circuit breakers do not have curves B, C and D as we already know in mini circuit breakers, however we have other curve classifications which are:

  • L (overload protection)
  • S (short delay protection)
  • I (instantaneous short-circuit protection)
  • N (neutral protection)
  • G (earth fault protection)

Unlike mini circuit breakers, the protection of open and molded case circuit breakers is not only with thermomagnetic overcurrent triggers, there is protection with electronic overcurrent triggers. The option of protection through a microprocessed electronic unit is called ETU (Eletronic Trip Unit). According to the needs of the project and installation, the technician or engineer will choose which of these protections will be necessary for its installation.

Curves of open circuit breakers and molded case circuit breakers.


The technical term used in electrical to turn circuit breakers on and off is called circuit breaker maneuver . To perform the operation of the open circuit breakers, the use of a lever for loading (compression) of the internal spring is used. This lever must be moved a few times until the spring is loaded, it is necessary to keep compressing the spring in several operations to lower the lever.

The moment the spring is loaded, the front of the open circuit breaker will indicate that the spring is loaded, thus changing from discharged, which means discharged to charged, which means charged.

Spring loading, discharged, charged.

After that we press the close button, the spring transfers the accumulated energy to the contacts, closing the contacts and allowing the passage of electric current between the open and closed busbars. To turn off, press the open button, so the contacts open, not allowing the passage of electric current between the input and output busbars of the open circuit breaker.

Closing close contacts, to open open contacts

Another option to close the contacts of the open circuit breaker would be through the electrical activation of a motor to load the spring in sequence, the activation of a coil, thus allowing the circuit breaker to be operated remotely.

The process for maneuvering mini circuit breakers and molded case circuit breakers is done by maneuvering a lever that does not have a spring, so when the lever is facing upwards it allows the passage of electric current and with its downward direction it does not allow the passage of electric current , being simpler than an open circuit breaker.

Maneuvering process of mini circuit breakers and molded case circuit breakers.


The technical norms and regulatory norms, aim to offer the possibility of carrying out a job or building a certain product, following minimum rules that prioritize safety, comfort and quality. And for safety another big difference between the circuit breakers is the standards.

The mini circuit breakers meet the standards NBR IEC 60947-2 and NBR NM 60898, these standards have requirements for circuit breakers for the protection of electrical lines in buildings and similar applications, designed to be used by unqualified people, so anyone can operate a mini circuit breaker.

Molded case circuit breakers and open circuit breakers, in turn, comply with the NBR IEC 60947-2 standard, in this standard it is clear that molded case circuit breakers and open circuit breakers must be installed and operated by people trained specifically for this purpose.

Maintenance and exchange

The maintenance is the procedure performed on equipment to ensure proper functioning and performance of the equipment, there are different types of maintenance, such as corrective, preventive and predictive maintenance. A difference from open circuit breakers is that unlike other circuit breakers, in open circuit breakers it is possible to open and perform internal maintenance on their parts, which is why it is called an open circuit breaker.