Milbank 200A MCB Trip Issue

[beanland]

Installed new Milbank 400A CL320 outdoor meter-main with two 200A Milbank labeled main breakers. We are having instantaneous trips at 400-500A; breaker magnetic element should not operate until 1200-2000A. Has anyone had similar problems?

 

[ATSman]

Your instantaneous trip range of 1200-2000A (6-10X) seems typical of molded case breakers of this type.
Need more info:
1. Are both breakers tripping?
2. How do you know the trips are from the Instantaneous element of breaker and not from Long Time element?
3. How are you measuring the trip current of 400-500A?
4. What loads are breaker's feeding?
5. What is Instantaneous trip set at?

 

[beanland]

breaker Tripping

breaker Tripping

1. Only one breaker connected
2. Per manufacturer TC, long time element is 2 seconds or longer, trips are faster
3. Fluke 43B capturing inrush event (1/2 cycle 400A RMS)
4. Additional loads are off
5. MCB built in IT 1200A min, 2000A max

Tested two 200A MCB in shop using high-current tester. Forum file upload does not work for me.