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Understanding different types of circuit breakers: A complete guide

- MCB (Miniature Circuit Breaker):

* Used for low current circuits in homes and offices.
* Protects against overcurrent and short circuits.
* Does not provide protection against earth faults.

- ELCB (Earth Leakage Circuit Breaker):

* Protects against earth faults by detecting leakage currents to the ground.
* Older technology, replaced mostly by RCCBs.

- RCCB (Residual Current Circuit Breaker):

* Modern version of ELCB.
* Detects and isolates leakage currents to protect against electric shocks and earth faults.
* Does not provide overcurrent protection.

- MCCB (Molded Case Circuit Breaker):

* Used for higher current applications than MCBs, typically in industrial settings.
* Provides protection against overloads, short circuits, and sometimes earth faults.

- ACB (Air Circuit Breaker):

* Used for high-voltage applications (up to 15 kV).
* Interrupts the arc in open air.
* Commonly used in industrial plants and power distribution systems.

- VCB (Vacuum Circuit Breaker):

* Suitable for medium and high-voltage applications.
* Uses a vacuum to extinguish the arc.
* Highly reliable, low maintenance, and long-lasting.

- MOCB (Minimum Oil Circuit Breaker):

* Uses a small amount of oil to extinguish the arc.
* Older technology, less commonly used today due to maintenance issues.

- BOCB (Bulk Oil Circuit Breaker):

* Uses a large volume of oil for arc quenching and insulation.
* Bulky and requires high maintenance; mostly replaced by modern breakers.

- SF₆CB (Sulfur Hexafluoride Circuit Breaker):

* Uses sulfur hexafluoride gas for arc quenching.
* Suitable for high-voltage applications.
* Highly efficient but more expensive and requires careful handling of SF₆ gas, which is a potent greenhouse gas.

- Summary:

* MCB and RCCB: Low-voltage and residential use.
* MCCB: Higher current and industrial use.
* ACB, VCB, and SF₆CB: Medium-to-high voltage and industrial or power grid applications.
* MOCB and BOCB: Older oil-based technologies.
* ELCB: Replaced by RCCB for earth leakage protection.

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.

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.

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
https://webstore.iec.ch/publication/65448