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Contact Resistance Testing and Circuit Breaker Performance

Product Line:
MCCB

Resolution:
Contact resistance testing is intended to be a predictor of breaker thermal performance while in service.  However, it is not a design specification and new-breaker contact resistance is subject to wide variation due to factors such as resistive oxidation from the manufacturing process and environmental factors after manufacturing.  The arbitrary standards suggested by NETA and other testing procedures result in many false negatives and should not be relied upon as the sole predictor of breaker thermal performance.
 
For those customers who want to do contact resistance testing, we recommend accepting the breakers that are within the limits acceptable to the customer on the first pass, and for those breakers that are outside those limits on the first pass we recommend load bank testing at rated voltage and current, or conditioning the contacts as described in the letter and re-testing.  Breakers with acceptable performance in service or during load bank testing are good and will not be subject to warranty replacement due to contact resistance test results.
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