Premium Membership ♕

Learn from experienced engineers and study specialized technical articles, guides & courses. Save 50% on courses with the Enterprise Plan.

Home / Technical Articles / What is the short-circuit switching (making / breaking) capacity?

Definition of switching capacity

The switching capacity is the r.m.s value of a current at a given power factor cos φ as well as a given rated voltage at which a switchgear or a fuse can still shut-off under specified conditions in an operationally safe way.

Short-circuit switching (making/breaking) capacity
Short-circuit switching (making/breaking) capacity

Both the short-circuit making capacity as well as the short-circuit breaking capacity of circuit breakers must be larger than or equal to the prospective short-circuit current at the place of installation.

If this is not the case, then a suitable backup protection (for example a fuse) should be provided to ensure the required switching capacity of the device combination. Data regarding devices for backup protection are given in the technical documentation.

Rated short-circuit making capacity Icm

The rated short-circuit making capacity Icm is a quantity that according to regulations must be in a certain ratio to the rated ultimate short-circuit breaking capacity Icu and that has to be guaranteed by the device manufacturer.

This is not a variable that must be considered by the user, however it ensures that a circuit breaker is in the position to connect onto a short-circuit – and to disconnect it subsequently.

Rated short-circuit breaking capacity ICU and ICS

IEC 60947-2 makes distinction between the rated ultimate short-circuit breaking capacity ICU and the rated service short-circuit breaking capacity ICS:

  Rated ultimate short-circuit breaking capacity ICU

ICU is the maximum breaking capacity of a circuit breaker at an associated rated operational voltage and under specified conditions.

ICU is expressed in kA and must be at least as large as the prospective short-circuit current at the site of installation.

Circuit breakers that have switched-off at the level of the ultimate short-circuit breaking capacity, are reduced serviceable afterwards and should at least be checked regarding functionality. There may be changes in the overload trip characteristic and increased temperature rise due to the erosion of contact material.

Rated service short-circuit interrupting capacity ICS

ICS values are usually lower than the values for ICU. Circuit breakers that have been switching-off at the level of the service short-circuit breaking capacity continue to be serviceable afterward.

In plants in which interruptions to operations must be kept as short as possible, product selection should be carried out based on ICS.

Breaking capacity of fuses

The same applies to fuses as to circuit breakers with respect to the ICU: at the given rated operational voltage, the rated breaking capacity must be at least as large as the prospective short-circuit current at the site of installation.

Reference: Low-Voltage Switchgear and Controlgear – Allen Bradley

Premium Membership

Get access to premium HV/MV/LV technical articles, electrical engineering guides, research studies and much more! It helps you to shape up your technical skills in your everyday life as an electrical engineer.
More Information

Edvard Csanyi

Electrical engineer, programmer and founder of EEP. Highly specialized for design of LV/MV switchgears and LV high power busbar trunking (<6300A) in power substations, commercial buildings and industry facilities. Professional in AutoCAD programming.


  1. Hussein Yahya issa
    Aug 10, 2016

    Please, I am an electrician with diploma in electrical and electronics engineering, am looking a job

  2. peter andong
    Jun 10, 2014

    Im in chargeman l1 course

  3. peter andong
    Jun 10, 2014

    Email me friend

Leave a Comment

Tell us what you're thinking. We care about your opinion! Please keep in mind that comments are moderated and rel="nofollow" is in use. So, please do not use a spammy keyword or a domain as your name, or it will be deleted. Let's have a professional and meaningful conversation instead. Thanks for dropping by!

Enter Captcha Here :

Learn How to Design Power Systems

Learn to design LV/MV/HV power systems through professional video courses. Lifetime access. Enjoy learning!

Subscribe to Weekly Newsletter

Subscribe to our Weekly Digest newsletter and receive free updates on new technical articles, video courses and guides (PDF).
EEP Academy Courses - A hand crafted cutting-edge electrical engineering knowledge