Introduction

In the electrical industry, contact resistance testing is often a component of an acceptance test procedure, and is intended to be a predictor of circuit breaker thermal performance when placed into service. It would be more properly called “pole-resistance” testing because in a sealed molded case circuit breaker it is not possible to isolate the contacts, and so the test reading reflects the resistance of the entire current path and may include lugs or other terminating hardware, all of which will affect the measured resistance value. Understanding the variable factors affecting pole-resistance and correctly interpreting the test results will help avoid time-consuming and costly circuit breaker returns and/or replacement.