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.
A customer called MIDWEST to ask why we did something called a “Reset Test” on his circuit breaker. He said he has had circuit breakers tested by switchgear service companies for nearly 30 years and never ever saw something called a circuit breaker “Reset Test.” He has Square D circuit breakers, Westinghouse circuit breakers, General Electrical circuit breakers and newer Cutler Hammer circuit breakers. He checked some of his old test reports and found no “reset tests.” He had never used MIDWEST before, so he was pretty interested when we explained the reason and procedure for the reset test. The reason was a very pleasant surprise because it gave him greater confidence in the proper performance of his circuit breakers. MIDWEST started using the circuit breaker “reset test” many years ago. It’s not a standard test procedure. You won’t find it in the text books or instruction manuals. You will find it in MIDWEST’s Training Manual under ‘Scars,’ meaning experience. It’s a carry over procedure from testing old dashpot type air circuit breakers and insulated case circuit breakers and molded case circuit breakers. The reason for the test is that occasionally, seldom but occasionally, a circuit breaker will nuisance trip when put back into service after it has been high current tested. For example, a 1600 amp air circuit breaker, after high current testing, might nuisance trip instantly at 500 amps. Basically the over current device failed during the high current testing. This was far more common with older “non electronic” over current devices. New electronic over current devices are more reliable, but not perfect. Strange things happen. We are not talking about the service technician forgetting to put the settings back to the correct positions. We are talking about an actual defective device. The test only takes moments. In the interest of quality control, the reset test addresses the “consequences of failure” as opposed to the “probability of failure.”
Yes, we are paranoid about safety and quality.