Circuit Breaker: Construction, Working, Types & Uses

MCB (Miniature Circuit Breaker), Construction, Working, Types & Uses
MCBs are used primarily as an alternative to the fuse switch in most of the circuits.
A wide variety of MCBs have been in use nowadays in all areas of domestic, commercial and industrial applications as a reliable means of protection.

Air Circuit Breaker (ACB) – Construction, Operation, Types and Uses
Circuit breakers are widely used in industries as well as power system for controlling and protection of different parts of the circuit like switch gears, Transformers, Motors, Generators/Alternator etc., which leads the system stable and reliable


  1. Ann Moody says:

    A circuit breaker, designed to protect an electrical circuit, is an automatically operated electrical switch.

    Portable Generators

  2. Tomi Engdahl says:

    E-fuses: warming up to higher-current applications

    The brief note explained the ins and outs of e-fuses with respect to these regulations, and it also reminded me of a point that it’s easy to overlook: fuses protect against overcurrent situations and the risk they pose to systems and people. They are not for high-voltage protection, even though we may unconsciously associate “danger” with AC-line voltage of 120/240V and the large amounts of current AC lines can deliver. The TI note lists approved e-fuses that go up to 4.5 to 60V at 6 A – clearly not line voltage, but still a substantial amount of current and double-digit voltage. Protection against high-voltage events is not a task for a fuse; instead, that is the role of MOVs, spark gaps, and other components.

  3. Tomi Engdahl says:
    For industrial LV installations the relevant IEC standards are, or are due to be:

    60947-1: general rules
    60947-2: part 2: circuit-breakers
    60947-3: part 3: switches, disconnectors, switch-disconnectors and fuse combination units
    60947-4: part 4: contactors and motor starters
    60947-5: part 5: control-circuit devices and switching elements
    60947-6: part 6: multiple function switching devices
    60947-7: part 7: ancillary equipment
    60947-8: Part 8: Control units for built-in thermal protection (PTC) for rotating electrical machines.

    IEC 60947-2:2016+AMD1:2019 CSV
    Consolidated version
    Low-voltage switchgear and controlgear – Part 2: Circuit-breakers

  4. Tomi Engdahl says:

    Failed elevator switch fuse / fusible disconnect

    This is a common industrial grade switch-fuse unit used for isolation and protection. The unit in this video had failed, so I thought it would be interesting to see what had gone wrong.

  5. Tomi Engdahl says:

    Defining short-circuit values for circuit breakers

    Circuit breakers protect electrical equipment from damage that may arise from short-circuit currents. However, the “short-circuit current” can vary depending on the application. How do IEC and EN standards help designers properly specify overcurrent protection in electrical equipment?

    Standards relating to circuit breakers
    Depending on the particular application, different standards may be referred to when a designer is specifying circuit breakers or associated equipment for power network protection:
    • The IEC/EN 60898-1 standard applies to circuit breakers for overcurrent protection in households and similar installations – for example, shops, offices, schools and small commercial buildings. These breakers are designed to be operated by uninstructed people and without the need for maintenance.
    • The IEC/EN 60947-2 standard applies to circuit breakers used mainly in industrial applications where only instructed people have access.
    • Switch-disconnectors are tested against the IEC/EN 60947-3 standard.
    • Switchgear assembly or distribution boards are tested against the IEC/EN 61439 standard.

    Due to the different scope of the standards, in some cases, different definitions are used for the same electrical process. The engineer must, therefore, ensure that he fully understands which particular definition, for, say, short-circuit capacity, applies to the design he is working on.

    Circuit breakers and IEC/EN 60898-1
    IEC/EN 60898-1 defines the rated short-circuit capacity (Icn) as the breaking capacity according to a specified test sequence.

    Circuit breakers and IEC/EN 60947-2
    IEC/EN 60947-2 defines the ultimate short-circuit breaking capacity (Icu), also known as the breaking capacity, according to a specified test sequence. This test sequence includes the verification of the overload release of the circuit breaker.

    Switch-disconnectors and IEC/EN 60947-3
    When switches, disconnectors, switch-disconnectors or fuse-combination units are included in a design, the IEC/EN 60947-3 standard is used. A switch-disconnector is capable of switching on and off a current under specified conditions. In the open position, the switch-disconnector provides an isolation function.

    As the switch-disconnector is not equipped with an overcurrent release, it must be protected by an MCB, MCCB or fuse. The short-circuit capacity of the combination of switch and circuit breaker is defined as the rated conditional short-circuit current.

    Low-voltage switchgear and IEC/EN 61439-1
    IEC/EN 61439-1 applies to low-voltage switchgear and controlgear assemblies. For assemblies with an SCPD in the incoming unit, the manufacturer must indicate the maximum prospective short-circuit current at the input terminal of the assembly. To protect the assembly, the Icu or Icn of the SCPD must be equal to or higher than the prospective short-circuit current. If a circuit breaker with a time delay is used as an SCPD, or no SCPD is incorporated in the assembly, the Icw with the maximum time delay must be stated.


Leave a Comment

Your email address will not be published. Required fields are marked *