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Back to basics: The fundamentals of circuit breakers

16 May 2021

Electricity is easy to take for granted, yet it’s extremely volatile ­­– with the potential of causing disaster. This is why circuit protection is so important. Circuit breakers are designed to prevent this type of trouble. This automatic circuit protection system will “trip” or instantly shut off the affected circuit – ensuring you and your devices remain safe.

What are circuit breakers?

A circuit breaker is an automatically operated electrical switch that protects an electrical circuit from damage caused by an excess overload or short circuit. The general function of a circuit breaker is to interrupt flow after a fault has been detected. In other words, circuit breakers cut off the electricity supply of the installation and allow for its restoration when the issue has been solved.

Compared to a fuse, which needs to be replaced once it has interrupted an overcurrent, circuit breakers can be reset and resume to normal operation. The generic function of a circuit breaker or fuse is often abbreviated as OCPD (Over Current Protection Device) as they remove power from a faulty system.

Circuit breakers come in many different sizes, including small devices which protect low-current circuits to large switchgear that protect high voltage circuits for an entire city.

Voltage switch board with circuit breakers
Voltage switchboard with circuit breakers

Even though low and medium voltage circuit breakers come with unique designs specific to amperage, voltage and application, there are five universal components that the various circuit breakers out there have. These include:

  1. Frame. This protects the internal part of circuit breakers.
  2. Operating mechanism. This enables the opening and closing of the circuit breaker.
  3. Contacts. This allows current to flow through the circuit breaker when closed.
  4. Trip unit. This opens the operating mechanism in case of a prolonged overload or short circuit.
  5. Arc extinguisher. These arc when the circuit breaker interrupts a fault.

Benefits of circuit breakers

 Circuit breakers come with many benefits, including:

  • They can be reset after interrupting an overcurrent event
  • They require no maintenance
  • They come with optional protective features

Different types of circuit breakers

You can classify a circuit breaker considering multiple criteria. Those focused on use-function include:

  • Power circuit-breakers. These are installed in the connection of an electrical panel from a generator, transformer, etc.
  • In consumer circuit-breakers, the connection is direct, located as close as possible to the load.
  • Distribution circuit breakers protect the conductors that connect the distribution panel with another part of the installation.

Another criterion includes the type of use:

  • Industrial use. This means it needs to meet the IEC 60947-1 or similar standard/equivalent.
  • Domestic use. This needs to comply with standard 60898 or equivalent. 

Type of construction is another classifier:

  • Miniature circuit breakers, also known as MCB are usually DIN rail mounted and are commonly used for final consumption.
  • Circuit breakers are more robust than miniature ones, they can be used for currents up to approximately 1000 A.
  • Air circuit breakers apply to the highest currents, up to 6300 A.
Motor protection circuit breaker
A motor protection circuit breaker

When choosing a circuit breaker, here are some things to consider:

When choosing a circuit breaker, here are some things to take into account:

  • Rated operating voltage (Ue) is the voltage at which the circuit breaker operates in the conditions of the installation without disturbance. Circuit breakers will have different voltage ranges and voltage values in case of disturbances in the installation ­– something to keep an eye out for.
  • Rated current (In) is the maximum current value that can indefinitely circulate by a circuit breaker without exceeding the allowed temperature values.
  • Adjustment of the thermal trip current (Ith) is the current above which the circuit breaker will trip in case of overload.
  • Adjustment of the magnetic trip current (Im) is the current above which the circuit will trip in the occurrence of a short circuit.
  • The breaking capacity is the value of the short-circuit current that a switching device can interrupt under a given voltage. When choosing your circuit breaker, think according to the values defined in the IEC 60947-2: Icu (ultimate breaking capacity) and Ics (service breaking capacity). Make sure this value is greater than the maximum short-circuit current expected at the point of installation.

Popular circuit breaker categories on Marketplace 

There’s a range of different circuit breakers listed on Marketplace. Let the links below guide you or use the simple search tool on the site. Or why not take a shortcut? View all circuit breakers currently listed on Marketplace by clicking here. Don’t forget, as a first-time user on the site, you can claim an exclusive 5% off your first order – that includes the whole basket. Claim your discount here.

 See the Lowest Guarantee Price badge on a circuit breaker you need? Know you can get that same circuit breaker cheaper elsewhere? Show us and we’ll match the price. Discover how it works and get started today.


Brand or Seller Product name Manufacturer Code
Siemens Siemens Circuit Breaker For Motor Protection, 2.2-3.2A, 3-P, 10 Ka, 690V, 3Rv2 Series 3RV2011-1DA20 
Schneider Electric Schneider Electric CIRCUIT BREAKER DT40A 2A UNI + NEUTRAL (D) SCHNEIDER SCHA9N21372 
Siemens Siemens Circuit Breaker For Motor Protection, 1.1-1.6A, 3-P, 100 Ka, 690V, 3Rv2 Series


Siemens Siemens Circuit Breaker for Motor Protection, 0.35-0.5A, 3-P, 100 kA, 690V, 3RV2 Series



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