Unexplained electrical danger in double box install

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Old 03-17-18, 11:11 PM
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Unexplained electrical danger in double box install

I am converting a duplex outlet into a quad with GFCI controlling both. I thought it was going to be easy but it is laborious. I
Anyway, there are three cables that converge in the old box and each is connected together by color, and a bare copper ground wire which is seperate from the cables. (Originally a two wire setup.
So I turned the breaker off and verified that the receptacles were dead. Also the bathroom light went out but not the bathroom outlet. But I was working on it and suddenly it threw an arc. When I checked the breaker box a second breaker was thrown.
At the current moment, with the breaker off but the second alluded to on I tested with an ac voltmeter and found no voltage on any of the wires or ground in any combination. So I am satisfied it is now dead.. I was very lucky not to get a shock.
Can anyone explain how it could be wired for this to happen? I discovered earlier that the water heater would still be partly alive if another breaker besides the normal one is not thrown.. In the long run I would like all these issues dealt with. In the present moment I am just installing a quad outlet in the kitchen where I won't need to keep unplugging things.
 
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Old 03-18-18, 03:07 AM
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Pictures would help but it sounds like you have 2 circuits going into box.
 
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Old 03-18-18, 04:55 AM
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I'm confused by this statement .......

So I turned the breaker off and verified that the receptacles were dead. Also the bathroom light went out but not the bathroom outlet. But I was working on it and suddenly it threw an arc. When I checked the breaker box a second breaker was thrown.

....... if you verified that the receptacles were dead, why did it throw an arc?

If the outlet you tested was a GFCI outlet, the GFCI outlet may have been tripped (dead) but not the breaker feeding power to the outlet? I suspect you turned off a 15 amp breaker that powers the lights to the bathroom and not the 20 amp breaker than powers the outlets.
 
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Old 03-18-18, 06:18 AM
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IF there was three cables (each with black, white and ground) and all the wires were connected by color (black to black, white to white, etc) the arc could have because you opened the neutral connection and there was a load on it. This will happen on a multi wire circuit.
 
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Old 03-18-18, 06:19 AM
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It is not unusual for two or more branch circuits to have wiring into the same box. Ideally things should be labeled but there is no code requirement.

But when two live cables enter the same box, their neutrals (and their hots) must not be tied together in any way, shape, or fashion. So you may see two wire nutted bundles of white wires. And a receptacle or other load connected to a given neutral must have its hot feed from the same circuit or feeding cable.

An all electric water heater and also a multiwire branch circuit is properly controlled by a double wide breaker unit or sometimes two single breakers that should be next to each other. The breaker handles should be tied together if it is not a double wide breaker with just one handle. If the water heater innards are still live until a third breaker somewhere is turned off then there is a wiring error or fault somewhere.
 
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Old 03-18-18, 08:40 PM
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I think you have nailed it, AllanJ. So all I need to do is run one of the pairs to the outlet and the other two pairs together? But whithout know where any of them go I am at a loss to know which pair belong together and which separate. They were all bundled together by color to begin with.
I now have it together and it works but I will take it apart again if I can correct it.
The same with the electric heate. The breakers are very different style from each other probably why they are not tied.
Ok, I get it. The two sets at the bottom each come from a separate fuse. The one at the top goes to the bathroom ceiling light. So it only matters which fuse they are on. I will route the one nearest the GFCI and route the other straight up. Then I should be cooking with gas! Thanks for the help.
But thid is assuming the power comes in from below. WhenI open it up and voltage test wires versus breakers all will become clear.
 

Last edited by richard123vmt; 03-18-18 at 09:00 PM.
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Old 03-19-18, 04:16 PM
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No, the two power line idea did not pan out,. I tried testing for voltage using both the breakers and only the crrect one produced voltage. The upper cable clearly controls the bathroom light. And furthermore, it is 14 wire suitable for the light but not to bring power in. Of the other two cables, I have verified that one goes to a second outlet at the other end of the counter. That leaves only the one cable to bring power in. So the wires are correctly bundled together and this is as it was before. It all works as it should so it leaves unexplained the arcing and the second breaker throw. My best explanation is I had failed to turn off the breaker, it arced and the second breaker went in sympathy from the vibration. Not satisfying but that is the best I can do.
Best conclusion yet: *i accidentally flipped the wrong breaker. Then I blew the correct one and both were tripped. I know that there is nothing else wrong.
 
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Last edited by richard123vmt; 03-19-18 at 07:03 PM.
 

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