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A closed breaker has voltage on the line side but low or no voltage on the load side.

Product Line:
MCCB's

Resolution:
All contacts have a minimum voltage and current required before they will conduct.  Usually this number is low enough so there is no problem with reading open circuit voltage on an energized breaker with no load, but on rare occasions the open circuit voltage on the load side will be reduced or prevented by resistive films on the contacts.  This film comes mostly from oxidation but could contain other contaminants as well.  

The solution is to put some load on the breaker, as then the current flow driven by line voltage will burn through the resistive film and the breaker will conduct and act normally from then on.  The amount of load required depends on the amount of resistance, but a low to moderate load should be enough. It may also be helpful to toggle the breaker as doing so will re-seat the contacts and help break through the resistance.
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