Electrical mystory

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Larry$

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Yesterday I went to the shop. There is some sort of electrical problem there. I can't tell what happened. Very odd. The breaker had kicked out to the CNC router, even though it wasn't being used. We turned the breaker back on and there was a loud buzz indicating a short circuit. But the breaker didn't kick out. Turned it off. That breaker serves a 208 to 480 volt, 3 phase transformer, that powers the router. On a totally different panel, a circuit for a 120 Volt outlet wasn't working, no breaker kicked. When the dust collector button was pushed (24 volt control circuit that operates the fan and rotary valve contactors) there was a noise and the lights in the laminating area blinked on/off, even though they were off. I turned the power on at my lathe. It made a buzzing sound. The DRO came on. When I tried the spindle motor nothing happened (3 phase.) I tried the Mill, which is on a different circuit and it came on fine (3 phase.) We tried the exhaust fan for the spray booth and it came on fine (3 phase.)

Strange series of things. The main breaker panel is 400 amp 3 phase Square D, I-line industrial grade ($400 breakers.) The panel that the CNC router is on was added when more power to the shop was needed. It is a totally separate feed from the utility. 400 amp 3 phase. There are several additional sub panels. The latest one added is for the new offices. A breaker on it tripped while no one was using anything. It was one of those damn GFI breakers that are overly sensitive.

I have no idea how all this could happen at once.
 
Any thunderstorms in your area lately?

Tom
 
I would second den-den's thought. I've seen lights in a building flash and burn out with a pop, one at a time in a row like the old time flash bulbs. On other circuits the lights were dim, and clocks wouldn't work. A little searching found several loose neutral wires. I tightened them all down and there were no more problems.
 
3 phase doesn't use a neutral! Multiple different grounds. No thunderstorms. Two different service lines from the utility! Multiple different breaker panels. :apologize: @ 8:00am the router was fine, office breaker not tripped two hours later multiple problems! Only one person in the shop, no equipment running.
 
The utility could be having an issue with one leg of the 3PH power. I have seen this happen at work One leg was down to 75V and it was messing up all kinds of things from 1ph 120 to 1ph 220 and everything 3PH. Every thing that used that leg was screwy.

Two line from the utility might still be fed from the same utility lines, Some things still draw power even when off
 
Flyinfool has a good point. Check the three phase voltages and see if they're equal (within reason). If they're good, I think I'd disconnect everything and check the voltages at each outlet before each device is reconnected, and also double check that each is being controlled by the breaker you think it is.
 
When we had the issue at work the utility found the problem about a half mile away from the plant in their lines. We were not the only plant affected.
 
Tomorrows project: start checking voltages but it will take a while. 25,000 Sq Ft. shop. A project that has been on the to do list forever is marking each outlet with the panel and breaker feeding. Then make a paper record, maybe a diagram. Several different electrical contractors have done work here. The last one just a week ago. My shop started out 4,000' 30 years ago. Many alterations since.
 
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