Whole Box became Hot

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  #1  
Old 04-21-04, 03:20 PM
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Whole Box became Hot

I am changing some wiring in a workshop that has a seperate 100amp service, with breaker box set-up for it. Several of the boxes were just wired and covered without any outlets installed. I selected one today - a single 12/2 wire from Breaker to box at wall. Wired a 20amp outlet - black to bronze screw, white to silver screw, pigtailed bare to a piece of bare to ground screw attached to box and piece of bare to ground screw on outlet. When I plugged in a trouble light and turned on breaker the bulb blew. I rewired with a different NEW (out of the box) outlet - this one a 15amp outlet with back stab connections - same type connections. Turned breaker on without having light plugged in - grabbed metal box to plug in light and got major shocked. It's almost like the ground wire is hot? I have not traced the wire from the outlet box all the way back to breaker (have to move some insulation out of the way to do that) - Any ideas what I might have going on here? I do not know what this circuit was used for before - as I said, it was left unhooked and covered when I got there.

Thanks in advance for your help - you've all been very helpful.
 
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  #2  
Old 04-21-04, 03:35 PM
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You have a short somewhere on the circuit, either because two wires are accidentally touching, or because you connected something together that should not be connected together, or because somebody drove a nail through a cable.

It's also likely that your ground wire isn't really properly grounded. Perhaps because somebody incorrectly thought you could ground it by attaching it to a plumbing pipe or a ground rod in the earth or to the neutral wire (which might be open). It is a common misconception that you can ground an outlet this way, and this kind of thing happens all the time. Rather than adding safety, it adds danger as your experience indicates.
 
  #3  
Old 04-21-04, 03:40 PM
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Questions:

1) Metal box with romex feed, or metal box with metal raceway (conduit), or something else?

2) Describe the breaker that you turned on to send power to the box.

3) Did you bother tracing _in the panel_ the cable that feeds the box?

It is entirely possible that the panel is wired incorrectly, and that the bare wire is connected to a supply bus rather than the grounding bus. Additionally, since this is a sub-panel, it is possible that the subpanel is not properly grounded. I would suggest turning off the feed to the subpanel, opening it up, and tracing the wiring.

Make certain that the feed to the subpanel has separate ground and neutral wires. Make certain that there are separate ground and neutral buses. Finally, make sure that the white wire to your receptacle is going to the neutral bus, and the bare wire to your receptacle is going to the ground bus.

-Jon
 
  #4  
Old 04-21-04, 03:59 PM
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Using metal outlet box - wire is romex cable - runs from the breaker box and is stapled along the length of a ceiling beam. The breaker is labeled 20amp, but, I did notice that it looks different than the other 20amp ones (the toggle switch is more rounded rather than square like the others).

I am going to trace the wire all the way back to the breaker and see if I can find something wrong with it (staple or nail causing short) - and I will check the grounding situation at the breaker box too.

I'm pretty sure I have the outlet wired correctly - I've installed several others exactly the same on a different circuit for lights and all is good.

Thanks - sound like I have a couple things to look for.
 
  #5  
Old 04-22-04, 08:34 PM
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Something else that I would strongly encourage you to check:

Make certain that the subpanel in the garage is _properly_ grounded. This means an equipment grounding conductor that goes from a ground bus in the subpanel all the way back to your main panel. This conductor must be separate from your neutral conductor and must go back to your main panel, not to any other 'ground' electrode.

Also make certain that the box that you connected was properly bonded to the bare wire in your Romex. The fact that the box was electrified suggests to me that you do not have a proper ground which returns current to your main panel.

-Jon
 
  #6  
Old 04-23-04, 07:08 AM
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Is it possible that the original 12/2 wired box you attached to is wired for 220 volts, and that you put 220 volts across the light bulb? That would surely blow the bulb.
 
  #7  
Old 04-23-04, 07:49 AM
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I agree with racraft. The only reason for the bulb to blow is if the circuit is wired for 240 volts. Any other problem such as shorted wire or no ground will not cause the bulb to blow.
 
  #8  
Old 04-23-04, 10:26 AM
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Wow, you guys are right. I totally misread this one.

However, the grounding problem remains. In fact, the grounding problem and the high voltage problem may share a common cause. This could occur if the power company's neutral is disconnected. If you haven't solved this yet, I strongly suggest you call your power company to have them check their equipment and connections. This is a routine free service all power companies provide to their customers. If this theory is correct, the appliances in your house are at greater risk of damage the longer you wait. What happens to your lightbulb today could happen to your microwave tomorrow.
 
  #9  
Old 04-29-04, 11:44 AM
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You guys got it right. I checked the breaker more closely and see that it is a double pole - the circuit was set-up for 220. I am replacing it with a single pole 20amp to fix that part but am still nervous about the grounding situation. I will definately call the electric company and have them check the line coming into the house.

I opened up the sub-panel (it is 100amp from the main box). And checked all of the wires coming in, looks to me that all of the ground wires are attached properly. I also traced the 12/2 romex from the receptacle across the ceiling and to the box. I can't find any obvious damage, no staples through the casing or anything that looks like it might be shorting it out.

I thought about putting in a junction box between the breaker and the receptacle - I could try to ground it there and then run a couple seperate wires to the outlets from there - or completely replacing the 12/2 wire all the way from the breaker to the outlet.

Thanks - I'm getting closer.
 
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