ACB air circuit breakers

Icu describes ultimate short-circuit breaking capacity; Ics describes service short-circuit breaking capacity; Icw states the current the breaker can withstand for a specified short duration. Select against the prospective fault current at the actual voltage. For 4000H, the 100 kA ratings belong to AC 400 V; at AC 690 V the listed value is 85 kA. The associated Icw duration is 1 s. Do not combine ratings from different rows.

Main incomers and bus-ties serve many outgoing circuits. Coordinate their trip settings with downstream breakers so a local fault can be cleared at the appropriate level. Any intentional short-time delay must remain within the breaker and busbar withstand limits. Check the complete protection curves and settings together; selecting a high breaking-capacity frame alone does not establish selective protection.

In ATMT applications, pair the breaker with the appropriate operating mechanism, position feedback and interlocks. Define permitted incomer and bus-tie states, loss-of-source handling and the capacity available when one source carries both sections. Include manual and maintenance modes in the sequence. Switching restores a supply path; a separate UPS is needed where the load cannot tolerate the interruption.