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Explain "instantaneous override" and "close and latch" ratings

FA237963

23 January 2021

Issue:
Explain "instantaneous override" and "close and latch" ratings. What do they mean?

Product Line:
Circuit Breakers

Environment:
Masterpact and Powerpact

Resolution:
"Instantaneous override" and "close and latch" are fixed trip settings to protect the breaker when there is a very hight fault condition. These settings are usually set higher than the standard instantaneous setting and function without regard to any other settings.

"Instantaneous override" is a fixed trip setting to open the breaker quickly (under 25 ms) in the event of very large fault which exceeds the instantaneous override trip value.

"Close and latch"  is a fixed trip setting while CLOSING the breaker and remains in effect for 20 ms after closing the breaker. Close and latch is set lower than instantaneous override to protect the breaker in the event of CLOSING the breaker on an existing fault condition. After 20 ms, the breaker reverts to the "instantaneous override" setting.