IEC 60947 define ICS as the "rated service short-circuit breaking capacity" while ICU as the "rated ultimate short-circuit breaking capacity". The Ics is a percentage of Icu. For "Utilization Category B" breakers, Ics is always equal to Icu. An example for Utilization Category B breakers from our range is the Masterpact ACB series. The ACB range is the only range with Utilization Category B. MCCBs from our range (Compact NSX, Compact NS and Easypact MCCB series), however, are considered as "Utilization Category A" breakers and thus Ics is a percentage from Icu (not necessarily equal to Icu as in the case of Utilization Category B breakers). For MCBs, Ics is a percentage (usually 50~100%) of Icu as well. This is usually illustrated in the respective products' catalogues and datasheets.

Some breakers are "Utilization Category A" yet still Ics is 100% of Icu and this is considered to be an advantage for the breaker. By all means, you have to refer to the respective product catalogue which will illustrate clearly the values of Icu and Ics.

Please find attached an extract from the IEC illustrating the difference between "Utilization Category A" and "Utilization Category B" breakers as well as the standard percentages of Ics with respect to Icu. You can also find attached pages from some of our product catalogues (MCBs, MCCBs, ACBs) illustrating how Ics is expressed as percentages of Icu.

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