Please help dangerous situation- switch wiring

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  #1  
Old 05-26-14, 07:14 PM
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Exclamation Please help dangerous situation- switch wiring

I'm new to this forum but would like to ask a question. I recently purchased an older home. The light didn't work in the bedroom downstairs that has a connected bathroom.

I pulled the switch out of the wall and to my surprise it wasn't hooked up. The 'line' wiring from the breaker box was capped and the wiring going to the light fixture was not even stripped at all. Curious got to me so I turned the power back on and test the line wiring with a multimeter. Here's what I found:

Going white to black I have 90.1 volts
Going white to ground I have 116.3 volts
Going black to ground I have 15.7 volts

From what I can guess (everything is drywalled) the breaker only runs the bathroom and bedroom. As it is the only things in the house that lose power when the breaker is off. But going back to the theory here if I have a short or a ground-fault I wouldn't think the bathroom lights would even work. Everything else that is visible has normal values.

My next step is to get a thermal imaging camera and try to find a hidden junction box. So my question would be is there any advice or ideas you guys would have on my situation.
 
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Old 05-26-14, 07:28 PM
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Lets not look for zebras yet.You have only looked at half the known circuit. The other known half is at the light.

Are you using a digital multimeter? They are more prone to false readings. Verify it is working correctly by measuring a known good circuit. Don't trust voltages readings less than 90 volts as accurate if digital. If you have an analog multimeter use that.
 
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Old 05-26-14, 07:47 PM
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Do you have a single two wire cable there ?
You're describing a switch loop.
 

Last edited by PJmax; 05-26-14 at 08:46 PM. Reason: gone zebra hunting
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Old 05-26-14, 09:16 PM
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Ok here we go. I checked a known circuit, meter seems good. It's a digital multimeter.
The only three wire cable from what I can see goes from the junction box behind the bathroom light to a outlet in the bedroom. I will try to upload some photos to hopefully make sense of it all.
 
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Old 05-26-14, 09:19 PM
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In the junction box for the bathroom light, the red and black wires that are crimped together have continuity with the black (switched wire) on the bathroom light switch.

So the whole reason for this post is to try to make sense of the bedroom wiring before installing the switch. Would you say I'm safe to connect the blacks in the bedroom light switch then put the switch in between the whites? The weird voltage readings is what stopped me in the first place.

I'm positive the un stripped cable in the bedroom light switch goes directly to the fixture. On the un stripped cable I got 22 ohms from black to white and OL when I removed the bulb from the fixture.
 

Last edited by rsagen; 05-26-14 at 09:32 PM. Reason: Added info
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Old 05-26-14, 09:58 PM
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I see what is probably two switch loops in the third picture. In the picture of the switch I see a typical switch loop with expected voltage readings. The white brings power in and the black carries it back to the light. Have you tried wire nutting those together to see if the light works?

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Old 05-26-14, 10:16 PM
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Which wires did you want me to connect together? The bathroom light works off its switch already. I only opened it up to attempt to make sense of it all. I haven't tried connecting anything for the bedroom light switch. (The photo of the un stripped cable) I wasn't sure which wire should go where in that case.

Thanks for your help so far. I have to work in the morning so I will check back tomorrow evening and hopefully make something happen without burning the house down. Lol
 
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Old 05-26-14, 10:30 PM
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Connect the two wires I marked as a switch loop to see in the bedroom light comes on. Forget the unstripped cable for now. On the slight chance this may cause a short only flip the breaker on for a few seconds. If it trips don't try again. A safer way is to connect a light fixture with a 60 watt incandescent bulb to the two wires and use a 60 watt bulb in the bed room. If both glow only half bright then you are good to go to install a switch.

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Last edited by ray2047; 05-26-14 at 11:01 PM.
  #9  
Old 05-27-14, 07:06 PM
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I connected the wires and nothing happened with the light. So I rechecked everything. Turns out I didn't have any power to the bedroom outlet with the wires disconnected. However when they were connected I did have power at the outlet. So this leaves me to believe that sometime in the past a switch was installed to create a switch loop with the outlet only. So when the previous owner wired in the new light at the same time as dry walling the basement, he terminated the wiring in the switch box for the outlet switch loop. As well as unhooking the old switch for the outlet.

I verified the "unstripped cable" does in fact go to the light fixture for the bedroom by the ohm meter and an old extension cord.

From what I can see, the black wire from the switch loop goes back to the bathroom light junction box, is crimped to the only red wire, then proceeds to the outlet.

So I will try to explain what I would like to do in simple terms to see if it is proper.

Inside the bathroom junction box:
Remove the white wire that goes to the bedroom switch loop while leaving the bathroom white wire connected to hot.
Connect the now unhooked white to neutral.
Disconnect the only red wire from the black and connect the black to the hot bundle.
Terminate and cap the red wire

Inside the bedroom wall plate:
The white is now neutral and connect together with the white from the un stripped cable.
The black is now hot and connect with the switch and the final black with the switch.
(So it should remove the switch loop wiring for that switch and replace it with regular style. In turn the light fixture should work.

Now I'm left with an unpowered outlet.
So inside the outlet:
Remove the red wire from the hot side and cap it.
Remove the wire nut from the two black wires in the black of the box (hoping they are power) and either pigtail in a third for the outlet or wrap them around the outlet screws.
Leave white connected to neutral.

Wow what an essay this turned out to be. I think after two days I finally understand this mess.

What do you think.
 
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