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High Current Testing Old Circuit Breakers at Low Voltage

October 20th, 2009 Comments off

MIDWEST was testing power circuit breakers for a large manufacturer.  The electrician working with us thought we were joking when we said we were putting 6000 amps through his 2000 amp main circuit breakers.  We told him to grab the bus from the test set to the breaker and he could feel the vibration and heat from 6000 amps.  He could hear the loud hum of the test set and the vibration of the old circuit breaker used in their foundry.  He wouldn’t touch it until we touched the bus first.  He had that strange look of “I see it, but I just don’t believe it.”  We told him the output of the high current test set was going into a direct short and the output voltage was only a couple volts.  We had him measure the output voltage with a voltmeter.  Then he understood what was happening.  It doesn’t take much voltage to push a lot of current through a dead short.