Posts Tagged ‘interlock system’

Circuit Breaker Will Not Reclose

April 16th, 2010 Comments off

An all too frequent scenario experienced by customers working in power distribution involves an air circuit breaker which after having tripped open fails to close again. When racked-in and the breaker charged it may trip free when the close button is engaged. 


Running down the list of possible factors, there are several key culprits which come to mind. Topping the list is the breaker racking-in interlock mechanism.  This interlock system is designed to ensure the breaker is fully in the racked-in position, the contact fingers fully engaged with the bus contact stabs, before closing.  What often happens is all too typical. The close tolerances designed in the racking-in mechanism can get out of tolerance through use if you so much as breathe on it wrong, or so it may seem. Even out of the gate as new equipment, they can be quite finicky birds requiring some TLC to keep them working smoothly.


The fix can be as simple as removing the front cover of the circuit breaker and lubricating the racking mechanism allowing its resets and mechanicals to function properly. The mechanism’s dogs can get stiff preventing the mechanism from seating properly.


In other cases we look for evidence the breaker may be over-racked in the racked-in position, throwing the interlock system out of alignment.


The circuit breaker proper may be out of alignment in its cell. This is very bad and runs the risk the load side connections (the finger clusters) may not be seated properly on the bus stabs. This is a nightmarish scenario if somehow the breaker manages to close and becomes energized.


When part of a good maintenance program, an air circuit breaker can be expected to delivery good reliable service for many years to come.