What is a circuit breaker

Difference circuit breaker switch disconnector

What is the difference between circuit breakers and switch disconnectors? How do circuit breakers and switch disconnectors work?


Circuit breakers and switch disconnectors are installed both in their function as switches and for protection. For example, we operate switch disconnectors several times a day - namely when switching the light on and off.

But what exactly is a circuit breaker? And how does it differ from a switch-disconnector? Why are these switches actually needed? How do switch disconnectors and circuit breakers differ in their functionality? Are they only for professionals or is it also worthwhile for a layperson to install these switches? These and many other questions about circuit breakers and switch disconnectors are dealt with in detail in the following text. Read up on the world of these important switch types!



Due to the high demand, we have updated this article and added the question “When do you need a 3-pole or 4-pole circuit breaker or switch disconnector?”.

What is the difference between a switch disconnector and a circuit breaker?

In general, the switching devices are used for Switching or protecting equipment and operating personnel. They mainly fulfill the task of Activation, switching of short-circuit currents, load switching for example for motors and for protection against overcurrent and against electric shock for people.

In order to make it clear what the difference between the switches is, it should first be explained exactly what is meant by the respective switches:

What is a switch disconnector?

At a Switch disconnector, also under the name Switch disconnector known, it is, as the name suggests, around one Combination of load switch and disconnector.

With a Load switch are those switches that are meant for the simple Switching on and off control gear serve. An example from everyday life are usual light switchesthat we all use every day to switch the light on and off. This type of switch is mostly used in the low and medium voltage range and is normally switched by hand. However, load switches are not suitable for switching motors.

A Disconnector or separator however is a High voltage switchwho is about a very small switching capacity disposes. The switch position of a circuit breaker is clearly visible and the switches are also equipped with a Switching fault protection that prevents unintentional opening and closing under high loads.

A Switch disconnectors now combine the functions of a load switch and a disconnector and meets the requirements for both switch types.

What is a circuit breaker?

Circuit breaker are in contrast to the switches mentioned so far - and that's exactly where it lies big differencesuitable for high currents. In addition to operating and low overload currents, you can also high short-circuit currents and overload currents in the event of a fault turn on. This type of high voltage switch can die Maintain fault currents for the specified period and then they switch off safely.

According to their design, circuit breakers can basically be in open circuit breakers and molded case circuit breakers can be distinguished. The former are often with their English name (Air Circuit Breaker) ACB abbreviated and the latter with MCCB (Molded Case Circuit Breaker).

The housing of the MCCBs consists of one Insulating material and encloses the components of the switch. ACBs however, are specialized in keep the main contacts closed as long as possible. They are air-insulated and available as a basic switch without a chassis (fixed installation) and as a switch with a chassis (withdrawable unit).


Why do you need circuit breakers and switch disconnectors?

To have two live parts are not spaced enough apart or are not sufficiently insulated, it often comes to one unwanted voltage flashover. Such a voltage flashover occurs electric arcwhich often greatly shorten the service life of the affected components or even destroy them directly.

A well-known example from everyday life are those arcs that occur on high-voltage lines such as the overhead lines of railway systems when people get too close to the lines.

Also at Switches it can lead to an interruption of the current flow Voltage flashover between the contacts because the distance between them is not sufficient for the insulation during the separation process. If there is gas between the two contacts, this will be at high Voltage difference ionized by the voltage flashover and there is a gas discharge in the form of an arc.

Despite the actual separation, this arc continues to conduct electricity and contains so much energy that it does damage or destroy affected components can. Special components can do this Prevent and stop the phenomenon. Circuit breaker are equipped with the appropriate protection mechanisms and are therefore usually referred to as Network protection used. Switch disconnectors are also used to protect the components.

Are the switches recommended for both professionals and beginners?

Circuit breakers and switch disconnectors are suitable for anyone who does either Protect components or control the switching of your equipment want. These can be experts who may operate complex, high-quality systems or hobby electricians who have one of these switching devices for a small circuit with only a few integrated equipment.

Circuit breakers and switch disconnectors are Can be used for both professional and simple systems and have countless areas of application.


Where are circuit breakers and switch disconnectors used?

Circuit breakers are not only used in their function as Switching element, but also as Network protection used. Four different switch groups are used for low voltages:

  • Open Circuit Breakers (ACBs)
  • Molded Case Circuit Breakers (MCCBs)
  • Switch disconnectors and circuit breakers
  • Motor protection switch

in the Medium voltage range Circuit breakers and switch disconnectors are also used. Here they are mainly used to switch objects such as transformers, generators, overhead lines, cables and the coupling of busbars.


How are circuit breakers and switch disconnectors constructed?

To the Main components the circuit breaker and switch disconnector include the following components:

  • thermal overcurrent release
  • electrical overcurrent release
  • Main contact system
  • Auxiliary switch
  • Switch lock
  • Extinguishing chamber
  • Drop anchor
  • Differential release slide

In the past, these components had to be installed individually, today they are installed in the switchgear itself and as a single unit complete component available.

Load switches are often after Principle of the so-called push-on switch built up. On the supports of the switch contacts are on this model Extinguishing devices for arcs built-in. Here, hard gas or a vacuum is used to extinguish.

Also one visible isolating distance can be found inside switch-disconnectors. The length of the isolating distance depends on the required insulating capacity in the respective application. The switches are switched using a Spring-loaded drive.


What types of circuit breakers and switch disconnectors are there and how are they differentiated?

Circuit breakers and switch disconnectors are used Depending on the area of ​​application in the most varied of variants and designs produced. Important Distinguishing features are:

  • Number of poles
  • Extinguishing agent
  • Switching principle

Circuit breakers come with both one as well as three or four poles produced. You can according to the way of Arc extinction in circuit breaker with Zero point deletion and circuit breaker with Short circuit current limitation be subdivided. The former extinguish the switching arc when the alternating current crosses zero, while the latter limit the surge short-circuit current to a small forward current.

Which extinguishing agents are used for circuit breakers and switch disconnectors?

For the switches that are in the High voltage area are used, different extinguishing agents are common in the production. These vary depending on the area of ​​application.

Even if aira relatively low extinguishing ability has, it still is nowadays insulating used. The circuit breakers that work with air as an extinguishing medium, however, require a relatively large amount of space. In the past, the air was compressed in specially designed systems and used by means of nozzles to blow out emerging arcs.

In so-called Vacuum switches there is a vacuum between the contacts and this is how the Creation of an electric arc directly prevented. This technology is mainly used in medium-voltage systems.

Also oil has been often used as an extinguishing agent in the past used in the named oil switches. Nowadays, however, low-oil circuit breakers can only be found in High voltage networks Application. The arc has a sufficiently high temperature to decompose part of the oil and convert it into gas. This gas pressure creates an oil flow and this extinguishes the arc.

By now, most of the oil switches have been replaced by the more powerful and efficient ones SF6 circuit breakers replaced. The Sulfur hexafluoride gas (abbreviated: SF6) is most often used in circuit breakers as an insulating gas, because its great thermal conductivity and high electrical strength particularly suitable for erasing.

What are the different switching principles?

Circuit breakers can also be used according to the respective Switching principles can be distinguished. A basic distinction is made here:

  • non-encapsulated switches
  • encapsulated switches

With non-enclosed circuit breakers those switching devices are meant that not shielded from the ambient air are. They are used in both Control cabinets as well as outdoors. Since there is no shielding, the ambient air can be used as an extinguishing medium.

Encapsulated switches however are shielded from the environment. This is done through the Installation of pipes, surrounds and housings. As an extinguishing agent must therefore Extinguishing media other than the ambient air can be used.

So-called 2-chamber or compressed gas switch use air as an extinguishing agent but are not widely used these days. Blow piston switch extinguish the arc with the help of a blower cylinder which, by increasing the pressure, finally causes the insulating gas to escape and extinguishes the arc.

Auto-blow switch operate on a similar switching principle as the blow piston switches, but use the energy of the arc itself to compress the gas and are therefore significantly more energy-efficient. So-called Flow switch are mainly used for alternating voltages in high-voltage networks and mostly extinguish with the already mentioned SF6 gas.

Note: Switch disconnectors are available both with and without a fuse. A distinction is also made between the usual two-position switch-disconnectors and special three-position switch-disconnectors. Switch disconnectors with integrated fuse, which are used in the high-performance area, are designed for systems with three-phase alternating current, three-pole.


When do you need a 3-pole or a 4-pole circuit breaker or switch disconnector?

Circuit breakers and switch disconnectors are available in 3-pin (3P) as well as in 4-pole (4P) version. Therefore the question arises when how many poles are needed. The number of poles required depends on the requirements placed on the switching device, whether it only has to monitor and switch the outer conductor or the neutral conductor.

How do the currents behave in the three-phase alternating current network?

Ideally, they have The currents of the outer conductors with three-phase alternating current have the same amperage. Due to the phase shift, the currents in the network cancel each other out in the neutral conductor and it is no harmonic component contain.

In practice, however, it can happen that the Unbalanced outer conductor loaded with different currents are and become one equalizing current on the neutral conductor to lead. The current strength of this compensating current can correspond at most to the greatest current strength of an outer conductor.

In addition, between the currents of the outer conductor can also Phase shifts occur and cause harmonics. In this case lead Superimpositions in the neutral conductor to currents that have a higher current strength than the largest value of the outer conductor. It can become one Line fire come.

When does the neutral conductor have to be monitored and switched?

It applies to one symmetrically designed consumers or a symmetrically designed system to protect comes in 3-pole circuit breaker or switch disconnector for use.

Should the three outer conductors and the neutral conductor are monitored and switched will come in 4-pole circuit breaker or switch disconnector for use. This is the case with one asymmetrical load on the outer conductor and if there is a risk of overloading the neutral conductor due to harmonics.

Note: There are also circuit breakers and switch disconnectors that secure three outer conductors and also switch off the neutral conductor when triggered. They are marked with 3P + N.


What accessories are there for circuit breakers & switch disconnectors?

Corresponding Switch accessories can support or supplement switching devices in their function. Examples of helpful accessories are:

  • Residual current blocks
  • Direct rotary drives
  • Auxiliary contacts
  • Alarm contacts
  • Function trigger
  • Locking devices

Residual current blocks, called FI blocks for short, serve as Fire protection and for operating personnel to protect against electric shock. They are usually equipped with an LED display of the fault current, an electrical test button and a reset button to reset the trip. The fault current circuit warning is given by an acoustic or an optical signal.

Direct rotary drives serve for the Change of state of the circuit breaker to ON or OFF. A rotary drive can also lock the switching mechanism and operate objects with the help of an extension shaft. Motor drives, on the other hand, make it possible to switch a circuit breaker remotely. This means that this activity does not have to be carried out manually.

Auxiliary contacts, often abbreviated as AX, indicate whether a Circuit breaker is in the closed or open state. With the help of Alarm contacts however, it can be shown that a Circuit breaker has tripped due to earth fault, short circuit or overload. These contacts are often abbreviated as AL.

Should one Interruption of the voltage does not automatically lead to shutdownso can Shunt release, SH for short, for Remote release be used. Also Undervoltage release, abbreviated to UV, allow circuit breakers and switch disconnectors to be triggered remotely.

If the lever of a circuit breaker is in the off position, this can be done with a Locking device for example locked with a padlock to prevent it from being switched on.

Note: If you need accessories for the respective switching device, pay attention to the compatibility of the components and coordinate them with one another.


What should be considered before buying a circuit breaker or switch-disconnector?

Whether you are a professional or a beginner, you should Carefully plan the application scenario before purchasing a circuit breaker or switch-disconnector.

Before buying an LTS or LS, ask yourself questions like:

  • What should the switchgear be used for?
  • For switching or should it also take on a protective function?
  • Will the switchgear be exposed to high currents or voltages?

Work out a Concept of planned circuit. This can be a small private switchgear or a large industrial system. Also note whether there are certain Pressure and temperature conditions that could influence the operating behavior of the switching device.

Tip: If you are unsure about the choice of switch or other issues, please contact our customer service.We would be happy to advise you and help you choose the right switchgear!


Which companies are among the leading manufacturers?

Circuit breaker ABB Stotz S&J via circuit breaker Eaton through to circuit breakers Gaunt Electronics experts are usually well known. Other leading manufacturers are Doepke, Salzer as Helios. Also circuit breakers Siemens are leaders in the market. Particularly well-known are the Siemens circuit breaker 3RV as Siemens fuse switch disconnectors.

Regardless of whether you are looking for a specific product or manufacturer or just want to have a look around, we are sure to have something for you. Just browse a little!

Difference circuit breaker switch disconnector