Understand In, Icu, Ics and Icw when reviewing circuit breaker ratings. See a real XUCKY ACB nameplate and learn which project conditions must be confirmed.
Circuit-breaker selection is not based on one number. Rated current, system voltage, prospective short-circuit current, operating continuity requirements and protection coordination must be reviewed as one project.
Four terms frequently appear in circuit-breaker discussions: In, Icu, Ics and Icw. Each describes a different part of the rating review. Confusing them can lead to an incomplete technical inquiry or an unsuitable comparison between products.
This guide uses a real XUCKY air circuit breaker image to explain the terms. Values visible on the photographed nameplate apply only to that photographed unit and are not a series-wide rating statement.
In is the rated current used as a key reference for the breaker rating.
For project review, In should be considered together with:
Expected load current
Conductor and busbar design
Installation method
Ambient and enclosure conditions
Protection settings and coordination
In is not a short-circuit breaking-capacity value.
Icu is the ultimate short-circuit breaking capacity. It describes the maximum stated short-circuit current that the breaker can interrupt under defined test conditions at a stated voltage.
A kA value should not be reviewed without its associated voltage and product documentation. The prospective short-circuit current at the installation point must be established by the project designer or engineer.
Ics is the service short-circuit breaking capacity. It is linked to defined service-performance tests following short-circuit interruption.
For project review, confirm:
The relationship between Ics and Icu for the selected product
Required operating continuity after a fault event
Inspection and maintenance procedures
The exact product documentation and test basis
Do not assume that Ics and Icu are interchangeable.
Icw is the rated short-time withstand current. It describes the current that the breaker can withstand for a stated short duration under defined conditions.
Icw must be reviewed together with:
The stated time duration
Short-time delay requirements
Selectivity strategy
Upstream and downstream device coordination
Busbar and switchgear withstand considerations
A kA value without its time duration is incomplete.
A practical review sequence is:
Confirm the system voltage.
Establish the expected load current.
Determine the prospective short-circuit current at the installation point.
Define selectivity and continuity requirements.
Review short-time delay and withstand needs.
Match the breaker configuration and exact model documentation.
The photographed XUCKY ACB shows these visible nameplate markings:
AC400V
In 1600 A
Icu 80 kA
Ics 65 kA
Icw 50 kA / 1 s
They are shown only to demonstrate how rating information may appear on a real product. They must not be applied to another model or project without verification.
This guide is category-level technical education. It is not a protection study, coordination study, wiring diagram or final selection document.
Before selecting or applying a breaker, confirm the system conditions, project calculations, required protection functions, exact model configuration and approved technical documentation.
No. In is the rated-current reference. Short-circuit breaking capacities are described by other ratings such as Icu and Ics.
No. Breaking-capacity values must be read with the stated voltage and the applicable product documentation.
They describe different rating concepts. Icu relates to ultimate short-circuit interruption under defined conditions, while Ics relates to defined service-performance testing. Confirm the selected product documentation.
Icw concerns short-time withstand performance. The stated current must be read with its stated duration and the project's selectivity and short-time-delay requirements.
No. The displayed AC400V, In 1600 A, Icu 80 kA, Ics 65 kA and Icw 50 kA / 1 s values are visible markings on the photographed unit only.
