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A Masterpact MP breaker with an STR58U trip unit is nuisance tripping at low currents

FA164567

22/12/2016

Product Line:  
MASTERPACT MP, MC, M series circuit breakers (CURRENTLY OBSOLETE)

Resolution: 
The trip unit on a breaker tripping with low current levels should be replaced.
These are sold to Schneider Services only and they must do the replacement.
See Supplemental Digest 177, page 11-37 for catalog numbers.

The alternative is to replace the breaker with a Masterpact NW.  Retrofit work is required.