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Circuit Breaker – POJ with perfect test results

Sometimes MIDWEST’s Engineering Technicians in our Switchgear Shop like to do what the Engineers call “Play.”  The technicians call it serious research.  Sometimes their adventures are quite worthwhile, even enlightening.  Recently an Engineering Technician dropped a circuit breaker test form on an Engineer’s desk and said, “Would you take a look at that and tell me if you think it’s okay.” The test results were excellent.  The contact resistance, insulation resistance, over current test results, reset tests, all the test results were excellent.  So why in the world was the Engineering Technician dropping it on the Engineer’s desk when the test results were so good?  The results looked like those for a new circuit breaker.  What they had done was test an old Westinghouse circuit breaker that had been practically crushed.  The case was broken and the arc chutes damaged.  It looked like it had been dropped from 50 feet and hit on one corner.  But, oddly enough, against all reason, it operated mechanically and the test results were all good.  But, of course, it failed the visual inspection.  When the Technician dragged the Engineer to the Switchgear Shop to evaluate the breaker, everyone had a good laugh.  This was good fun and the technical evaluation was unanimous, POJ, Piece of Junk.  One of our favorite highly technical terms.  In this case it was very obvious.  But frequently we find defects in used circuit breakers and in brand new circuit breakers, and other electrical equipment, that would never be revealed by testing alone.  That’s why the experience, training and knowledge of the Technicians and Engineers are extremely important.  There is no perfect test standard for every POJ.

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