All, I would like to pic your brains. I acquired a stacco 5010-3Y, its labeled as a 240V 3 phase unit set at 0-280 out. 50A per core. Only 3 terminals per core. Clearly marked. I'm running it on a 30A breaker at the moment. With no load you'd think that would be fine. Sounds great, except I can't get the darn thing to operate. Pops the breaker every time. Makes a hellacious 60hz hum in the process on all the cores. This is with it connected to nothing on the output, just applying voltage. Logically I checked for anomalous resistances, everything showing proper isolation.Visual inspection doesn't show anything noticable, Brushes and contact surface looks good. One of the cleaner units i own.. Inrush current seemed to be the next logical thing to try, got a 35A CW rated varistor 2 to.02ohms (i only wanted to run these at 30A for the time being) which promptly exploded. A relay shorting a high power 6ohm resistor was the next step. Powered on at 240v with series resistor for about 5 seconds then kicked on the relay to remove the resistor, bzzzzzzz pop goes the breaker. No magic smoke or smells of burnt enamel. Unfortunatly I havnt been able to observe the actual current its drawing yet. But I will set up a scope in the near future to record it. I've brought many variacs back into service, as have many of you. But this is the only one thats been a real head scratcher. Next step is to pull the top plate and see if anything is going on in the middle with the connections, but alas Its not like I'm reading any shorts. There are 3 little inductors or something that seem to be inside each core. I assumed they were on each input/output to act as a current limiter of some sort. But ill have a better look when I pull the cover and go over a core with a fine toothed comb.Anyone have any ideas of what I could be looking for or potential causes. What ever the matter is, it seems to effect all 3 cores. Unclear if the effect is equal on each core, but the result is the same. -Jay
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