Breaking capacity is the maximum prospective short-circuit current that a circuit breaker is rated to interrupt at a stated voltage and under specified test conditions. It is not the normal load current or trip setting. The required rating must be established from the prospective fault current at the installation point and checked against the exact breaker model, voltage, standard and manufacturer data.
A breaker with insufficient short-circuit capacity may not interrupt a fault safely. Selection and verification therefore belong to the electrical design process and should be performed by a qualified professional. Never create a short circuit to test a breaker, and do not use an ordinary clamp meter as a direct kiloampere fault-current test.
When a short circuit occurs, the available current can be many times higher than the normal operating current. Breaking capacity describes a circuit breaker’s tested ability to interrupt that current without creating an unacceptable hazard. Ratings are normally stated in kiloamperes (kA), but a kA figure is meaningful only together with the rated operational voltage, current type, number of poles, applicable standard and any stated conditions.
For example, a rating printed for one AC voltage cannot automatically be assumed at another AC voltage or on a DC circuit. Always use the complete nameplate and datasheet, not a product-family headline alone.
| Marking | Practical meaning | Selection note |
|---|---|---|
| Icn | Rated short-circuit capacity used in the IEC 60898-1 context for circuit breakers intended for household and similar installations. | Check the marked value, voltage and the requirements of the applicable installation rules. |
| Icu | Rated ultimate short-circuit breaking capacity in the IEC 60947-2 context. | It establishes an ultimate tested capability; it is not a promise of unrestricted continued service after a fault at that level. |
| Ics | Rated service short-circuit breaking capacity in the IEC 60947-2 context, followed by specified performance verification. | Compare both Ics and Icu when continuity of service and post-fault performance matter. |
| Icm | Rated short-circuit making capacity, expressed as a peak current. | It is not the same quantity as an RMS breaking-capacity value. |
These values are not interchangeable labels. The applicable term and test sequence depend on the product standard. Use the manufacturer’s published data for the exact catalogue number rather than converting one rating into another with a universal percentage.
Breaking capacity concerns interruption of a prospective short-circuit current. Making capacity concerns closing onto an existing fault and withstanding the first peak of the current. Because the initial peak includes an asymmetrical component, Icm is expressed as a peak value and can be higher numerically than the RMS breaking rating. The relationship is defined by the applicable standard and test conditions; do not apply one fixed multiplier to every device.
IEC 60898-1 applies to certain AC air-break circuit breakers for household and similar installations, within the standard’s stated voltage, current and short-circuit-capacity limits. Products in this context commonly display Icn. A familiar rating such as 6 kA or 10 kA must still be checked against the prospective fault current and local installation requirements.
Browse the OOHMAGE MCB range by pole count, rated current, trip curve and published short-circuit rating. Final selection must be based on the exact datasheet and project conditions.
IEC 60947-2 covers low-voltage circuit breakers intended to be installed and maintained by instructed or skilled persons. MCCB data commonly includes Icu and Ics at one or more operational voltages. The same frame can have different interrupting ratings by version and voltage, so frame size or rated current alone does not determine breaking capacity.
Review the OOHMAGE MCCB range, then verify the exact Icu/Ics table, voltage, trip-unit function, poles and coordination data for the selected model.
The design value is the prospective short-circuit current at the point where the breaker will be installed. It depends on the source, transformer, conductors, upstream network, parallel sources and system configuration. A simplified relationship such as current divided by total loop impedance can illustrate the principle, but a real installation may require a coordinated short-circuit study and appropriate verified input data.
A qualified professional may use network data, transformer data, cable impedances, an approved calculation method and suitable installation test instruments. An ordinary clamp meter does not directly measure a prospective kiloampere short-circuit current, and deliberately creating a fault is unsafe.
Do not select by adding an arbitrary percentage to a rough fault-current estimate. Any design margin should follow the governing rules, uncertainty in the study, future system changes and the responsible engineer’s documented method.
An upstream protective device may allow a downstream device to be used in a tested backup or cascading combination. This is not a general licence to combine arbitrary breakers. The manufacturer must publish the exact device pair, voltage, maximum prospective current and any other conditions.
Backup protection and selectivity answer different questions. Backup protection concerns the combined short-circuit capability. Selectivity concerns whether the nearest protective device clears a fault without unnecessary upstream interruption. Both should be checked against tested coordination tables.
Do not assume that a breaker is fit for continued service merely because its handle can be reset. Isolate the installation and have a qualified person identify the fault, inspect the equipment and follow the breaker’s manufacturer instructions. The appropriate action depends on the fault magnitude, device rating, visible or internal damage, test sequence represented by the rating and the manufacturer’s service guidance.
There is no universal rule that every Ics operation removes a fixed percentage of service life. Likewise, a continuity check with a basic multimeter cannot verify a breaker’s short-circuit performance. Replace or return equipment for assessment when required by the manufacturer, responsible engineer or applicable rules.
Standards are revised over time, and national adoptions or installation rules may add requirements. Confirm the edition and local rules that apply to the project.
No. Rated current relates to normal current-carrying and overcurrent-protection duties. Breaking capacity relates to interruption of a prospective short-circuit current under specified conditions.
No universal percentage applies to every circuit breaker. Use the exact Ics and Icu values published for the model and voltage.
No. Breaking capacity is a product rating established by standardized testing. Prospective fault current at an installation is determined using appropriate calculation data or suitable approved test methods; an ordinary clamp meter does not directly read the prospective kA value.
Resetting should not be automatic. The fault must first be identified and the breaker and installation assessed in accordance with manufacturer instructions and applicable rules.
For a product shortlist, send OOHMAGE the system voltage, AC or DC application, poles, rated current, trip requirements, prospective short-circuit current, applicable standard and required Icu, Ics or Icn. Our team can identify matching published product data for engineering review.
Contact OOHMAGE for MCB or MCCB product information. Final protection design, coordination and installation approval remain the responsibility of the qualified project professional.
