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Alarm on Hitachi can be tripped by breaker only, but breaker was not tripped.


Hitachi Generic alarm generated.

The alarm that was being generated had no description at all. On this particular Hitachi machine tool you must look at the diagnostic addresses on the Fanuc side which will tell you the alarmed bit. On this machine I had an alarm that could only be generated from a breaker trip circuit according to the electrical prints. However when the alarm occurred the breaker did not trip. I looked at what was in this breakers circuit and found that it was for multiple things. Air cooler exchange fans, cabinet fans, machine light and several other things.


The first most obvious things to check were the fans. They commonly freeze up from sludge and often go bad tripping the breakers. After looking at all the fans I found three fans bad. One fan was humming and not turning and the others were dead. I disconnected the CNC fans and let the customer run until new ones could be installed. I had made sure all the connections were tight. I told the customer if the alarm came up to disconnect the signal wire on the breaker to see if the diagnostic bit goes low. Doing this will prove if the breaker is false triggering the input or whether something else is shorting the input to generate the alarm.

In the end even though the breaker did not fully trip the input broke for a split second apparently when the amperage was just high enough to trigger the contact but not actually trip the breaker. Sounds strange to you? Me too but that’s how it turned out.