MCCB Stress on Contact Terminals

What sort of stress electrical or mechanical. Be more precise.

1/ do you mean the connection terminals or the contact tips

2/ what is the rating of the MCCB

3/ loading

4/ frequency of operation

Without information we can't give an answer!

1/ Between MCCB connecting terminal and panel busbar

2/ 450A, 3pole ABB make Breaker

3/ 250A - Constant Load

4/ per day min 5 times

I take it this is a follow on from your last thread, have ABB given any explanation for the failures?

What is it that is actually failing?

The closing mechanism can be stressed by bus bars putting torsional strain on the connections. I would suggest a short section of braided copper between the MCCB and bars.

But MCCB's aren't designed for repeated switching (check the MTBF)

To be honest this is a matter between you and ABB.

Rule #75.

Yes! Possible! Undue stress on the terminals might increase the temperature which might flow into the MCCB and char the inter-phase barriers. Thus causing MCCB Failure.

Possible, might, may, could be, maybe, if... there are myriad ways to say that anything is possible under certain circumstances, but I agree this is a matter to take up with ABB.

1/ how to check the stress between busbar and MCCB contact terminals?

2/ what is the tolerance?

If there's going to be any stress it will be apparent when the bus bars are offered up to the terminals. If you have to use any force to align the connections you will have stress. Incorrect termination, IE placement of washers, over tightening etc, will cause stress.

If there is any tolerance for stress it will be specified in the ABB handbook.

Get an ABB engineer in to show you how to fit a MCCB, with 4 failures you obviously don't know how to.