The category of use of a circuit breaker is defined by the product standard IEC/EN60947-2. This standard indicates 2 categories: A and B. Category A includes circuit-breakers without intentional tripping delays in the event of a shortcircuit, while category B includes circuit breaker with intentional tripping delays to guarantee selectivity. The motor protection circuit breakers must be in A category because they are designed to protect a single branch of an installation. Therefore they must not have delays to avoid the intervention of upstream circuit breakers that protect large sections of the system. This reduces the out of service to a single load on the line where the short circuit occurred.

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