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.
We had a conversation with a maintenance mechanic. He said he was a carpenter one day and an electrician the next, so he needed a little advice. He had some plastic circuit breakers that got washed down during clean up and, after they dried off, they looked great. But he wanted to know if he could still use them or if we could tell if they were okay. They were small single pole circuit breakers, a couple 200 amp circuit breakers, and one 1200 amp breaker. We call these molded case circuit breakers, but they are what everyone typically just calls circuit breakers. They also had some old obsolete bus plugs and some small transformers used for emergencies, that he just threw out. We told him to also throw out the little breakers and the 200 amp. Actually we told him to smash them so nobody would be tempted to reuse them. We have torn apart old and new circuit breakers after water damage and they are nasty inside. You do not want to reuse them. Very dangerous… Even if they worked mechanically, they could easily fail to interrupt load and turn into fireworks. We told him, if he wanted to, he could send us the 1200 amp breaker and we could take it apart and see if it could reliably be reconditioned. The chances of that are less than 50%. The real concern is whether or not the over current trip element in the circuit breaker got wet. If it did, it is very time consuming to take it apart and restore it to perfect working condition. And the quality control tests after the repair of a trip device are also time consuming. Many new circuit breakers have electronics which make reliable reconditioning after water damage almost impossible. One could do a simple clean up of a water damaged breaker and test it and it may pass all the simple routine tests. But internal inspection shows immediately that the circuit breaker, especially the circuit breaker trip device, is not reliable. We have seen water damaged used circuit breakers pass the basic insulation resistance, contact resistance, and over current tests, but fail our own additional special quality control tests. The internal inspection shows them to be in horrible condition. We find rust, free water, mud, and usually slime. If you have water damaged circuit breakers, just destroy them so no one thinks they are okay and tries to reuse them.