Re: finding 2 bucking circuits.
I love a good trouble shooting challenge. . .and this is one of the classics. Two breakers connected to what, arguably, should be two separate circuits.
The only reason that the trouble showed up is that the two breakers are on opposite sides of the panel, creating a 240 Volt short when both breakers are turned on. When only one breaker is on, everything is on. . .no outage area to help locate which openings to explore on that long circuit.
tshea's suggestion is good, and will help, if the occupants have knowledge of what has happened in the past. But sometimes no one knows.
I had a little old lady call 'cause she overloaded the circuit her computer was on, and, when she went to reset the circuit breaker, sparks and light erupted at the panel.
When I arrived and went to reset the two breakers that were tripped, the first one went fine (I heard the refrigerator kick on) and then, resetting the second gave me the visual and sound of a 240 Volt bolted fault. . .light and sound, flash bang.
Asking the lady about what might have happened informed me: </font>
- <font size="2" face="Verdana, Helvetica, sans-serif">She was a widow a year now.</font>
- <font size="2" face="Verdana, Helvetica, sans-serif">Her dead husband had done all the mechanical things.</font>
- <font size="2" face="Verdana, Helvetica, sans-serif">She didn't have much money and was trying to learn about taking care of things herself as best she could.</font>
- <font size="2" face="Verdana, Helvetica, sans-serif">The computer was on the kitchen table on a circuit with the toaster, refrigerator, coffee maker, microwave. . .six duplexes in all.</font>
- <font size="2" face="Verdana, Helvetica, sans-serif">The 240 volt fault had scared her badly and she was imagining financial ruin.</font>
<font size="2" face="Verdana, Helvetica, sans-serif">Well, I got to know her and the situation, but I didn't get the exact tech for which opening to go to first. So I started at the circuit breaker box, and traced the wires out into the circuit. . .well, well, they share a neutral. . .I looked at three j-boxes in the open basement ceiling and then separated the biggest splices, one each in the two hot conductors. I looked for continuity between the two hots and it was only in one pair. This lead me to the receptacle at the computer, and while I started to open it, the little old lady started reminiscing about how her hubby had done that receptacle over 12 years ago. . .
By now I've got the receptacle out of the wall, and, low and behold, there's the breakout tab still in place. I handed her the little piece of metal, remounted the receptacle and covered it; closed up the j-boxes in the basement; examined the breakers and bus. Here I found that hubby had tried to get by after giving up on finding the problem he had created. One breaker was loose and badly burned at the bus connection. He had blown the circuit a lot of times and finally left the one breaker on, but not in contact with the bus.
When she had done the first breaker reset, she had not known to leave it alone, and had wiggled it down to the bus while resetting the breaker handle. . .kapow!
All told, I spent 40 minutes, and I doubled the power available in her kitchen, taught her a lot about her system, helped her back to calm, and felt proud of myself.
In some respects, I was lucky on that one troubleshoot, but, the basic tools are there. Had the wiring between j-boxes been covered, that would have slowed me down.
