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?
The older version of that device, RMS-9, with the dials instead of
digital programmer, is great for tripping early. Out of an installed
base of 70, I have had 4 so bad that they failed with less than 25%
load. Although these units are LSI.
The short version is yes, it may be that the programmer is bad.
make sure that the electricity is not going backwards through the breaker.
Happens a lot especially in UPS and paralleling gear. Example top stabs are
line in and the bottom ones are line out. If this is not the case then
reverse the ct's and all should be better. Which may mean getting someone
that built it out so you do not loose warranty.
I assume you HAVE tested the breaker and the settings with secondary
I have seen bad trip units out of the box. You have looked at the TIME
setting for the LT, right?
Hope this helps