Withdrawable air circuit breakers

[Perthboy]

Can anyone guide me to good information regarding the "finger cluster" connections at the rear, where the ACB connects to the main busbars. I have a problem where they have failed and I want to change to a new technology. Someone has mentioned that this technology has failed in the past but I can't find any information.

 

[DougMSOE]

The weak point of the finger cluster design is the spring tension. Years ago when I was in field service we rec'd a bunch of "new" springs. These "new" springs failed very quickly because they could not keep tension within the req'd temp range. This lead to failures in the contact areas of the clusters. When we replaced the springs with the correct springs, the clusters worked fine with long life.
This whole episode lead to a better way of testing contact resistance both on the finger clusters and the contacts themselves. This new way uses the voltage drop across the subject "joint" when rated frame current is applied.
The Ductor method missed the "new" springs problem but was found with the voltage drop method.
Doug