A client has recently had problem with this breaker; it's 3 pole, 480 volts, 4000A frame, 4000A trip, electrically operated, drawount mounted. The trip unit is a MVT with LSIG trips. The breaker has been in service less than 6 months.
The breaker is installed in an UPS switchgear and opened without any instruction from the UPS system. A long time trip flag was indicated, with a LT setpoint of 5100A. Tripping on LT is dubious because the UPS cannot produce this amount of current for long enough to reach the LT range. The UPS would have to transfer to bypass to provide 5100A, but the UPS history log indicates nothing about such a transfer.
Anybody encountered anything similar?
Regards, Chris Johnston