soft starter still tripping main breaker

[krbernier]

i have 2 smc-flex soft starters running 350 hp motors at a water lift station. the main 1600a incoming breaker is tripping when one of the motors is shut off. sometimes it trips sometimes it doesn't. i finally got the use of a fluke 435 power quality meter and was able to record the main when it tripped.

i have a recording of a normal shutdown and a shut down with a trip.

when this happened both motors were running and only one was shut down. stop time is 15 seconds. im going to attach both recordings hoping someone with more knowledge can help!

 

[davidbeach]

You need to find someone locally who understands these types of systems. The problem can't be solved over the internet. Everybody that has answered here has woefully incomplete information about the problem and are offering ideas based on that incomplete information and you want to take stabs in the dark based on those suggestions.

Hire somebody that can find the problem rather than simply trying to find a way to mask the symptoms.