Ouch


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Posted by D Sherman [72.47.9.228] on Tuesday, August 09, 2011 at 18:09:14 :

In Reply to: Re: O.T. old welder problems posted by Jerry in Idaho [64.139.238.43] on Tuesday, August 09, 2011 at 17:40:46 :

Compressors REALLY don't like undervoltage. Brownouts are killers on refrigeration equipment for that reason. A few years ago we had a lot of trees falling across the wires in Wallace for several days. One of the trees apparently broke only one of the 3 distribution wires. Our electrical system downtown still consists of a sort of semi 3-phase system with open deltas and 2-pot banks -- one larger main transformer for most of the load, which is single-phase 120/120, and a smaller "stinger" transformer for the third phase, which there aren't too many of downtown. In this system, the center of the single-phase transformer is grounded, so all of the "corners" of the three-phase system are floating and of course a 4-wire wye is impossible. Somehow with this funky distribution system and one 12 kV wire broken, we were getting 60/60 out of the single-phase side of the system for quite a while until somebody or some automatic switch cut it off. All kinds of weird things happened: fluorescent bulbs stayed lit at full brightness. Regular bulbs were dim, but stayed on. Computers kept trying to reboot but never could. We went and unplugged all the refrigerators in the coffee shop as quickly as possible before their compressors burned up.

Your carpenter electricianing used to be the standard way to do it. I have old panels that were wired by union electricians decades ago that have neatly-installed pieces of copper wire to tie the breakers together. The system is okay if the wire is stiff enough (a nail is better), but usually it's too limp or loose and only one breaker trips. Still, it's strange that your compressor kept running because usually they're tied right across the 220 with no connection to neutral. I'm wondering if maybe you have a ground fault somewhere within your compressor? Check the side that tripped the breaker. If it shorted to ground, it would not only trip the breaker on that side, but it would then carry the current from that side to ground/neutral and allow the compressor to try to keep running at half voltage. You may have an intermittent short there that's going to cause more trouble in the future.



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