wall switch - power in when off but no power in when on

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Old 02-28-13, 04:02 PM
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wall switch - power in when off but no power in when on

Interesting situation I've not come across in the past. I've got a single pole light switch which operates several high hats. The lights were working erratically and not at all now. I suspect a bad switch. I pulled the switch cover and when the switch is in the off position, I've got power to the switch, however, when I flip the switch to the on position, my hot lead dies. When the lights were flickering, there was some buzzing coming from the service panel. I removed the cover and saw no carbon tracks or evidence of breaker failure to that circuit so I'm assuming this could only be a bad switch but the fact that I lose power to it when I flip it on doesn't make sense.

Ideas?
 
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Old 02-28-13, 04:11 PM
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No....the switch is ok. When you turn the switch on your applying a load to the circuit. That load is causing something loose or corroded to fail.

Probably best to start at the panel with a test meter or wired voltage tester.
 
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Old 02-28-13, 05:00 PM
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You mean check for 110 coming off the breaker and then trace it back to the switch to find the problem somewhere in the middle?

Also, I forgot to mention but, at the switch, there was the black hot lead coming to the switch and leaving the switch was a white wire taped black. Because of this, I drew what I believe the circuit must look like. I've attached an image. Does it sound like the switch is likely at the end of the circuit like I've illustrated. If so, does that change anything?

Thanks PJhttp://static.inky.ws/image/3744/photo%284%29.JPG
 
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Old 02-28-13, 05:07 PM
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Yes.....check the breakers for 120 vac.

You have a switch leg in that box. The hot wire goes to one of the light fixtures first and then a two wire switch leg is brought to the switch. Your taped wire is the blue one in my pic.
 
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Last edited by PJmax; 02-28-13 at 09:08 PM. Reason: clarified drawing
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Old 02-28-13, 06:43 PM
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when the switch is in the off position, I've got power to the switch, however, when I flip the switch to the on position, my hot lead dies.
It sounds to me like you are switching the neutral conductor and not the hot conductor. IF you are, with the switch off, the power will feed thru the light bulbs and come all the way down back down the neutral side to the switch and you'll get a 120 volt reading. Turning on the switch completes the circuit and the lights will come on, but you are switching the neutral side so you'll not get a 120 volt reading to ground with a meter.
 
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Old 02-28-13, 07:53 PM
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I highly doubt that Joe. Not to mention a properly wired switch will show 120v across the screws when off.. A high resistance connection somewhere along the line sounds much more plausible.
 
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Old 02-28-13, 09:14 PM
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I came back and redrew my illustration. Based on that it shows you that the hot feed is in one of the lights and a two wire switch leg is run down to the switch.

So the problem can also be at that fixture.
 
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Old 03-01-13, 04:48 AM
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@PJmax
I'll check it this weekend. Seems ridiculous to wire it this way. why would it have been done like that? so the hot feed goes into the fixture, then connects to what?
 
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Old 03-01-13, 05:00 AM
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Seems ridiculous to wire it this way.
Not ridiculous . Very common. This the way probably over half of all lights are wired. It uses less cable and is in some ways easier to wire.

so the hot feed goes into the fixture, then connects to what?
The switch loop (and often to the next light fixture in the next room of the house that needs power).

 
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Old 03-01-13, 03:19 PM
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so the hot feed goes into the fixture, then connects to what?
A wire feeding the switch.

If you look closely at the drawings that PJ and Ray posted you'll see that PJ shows the power going to the switch on the black wire and returning to the lights on the re-designated white wire (shown in blue). Ray shows the power going to the switch on the re-designated white wire and returning to the lights on the black wire.

That's not an error or sloppiness on their parts. PJ was drawing what you likely have now. Ray was drawing the way it should be done.
 
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Old 03-01-13, 06:37 PM
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I highly doubt that Joe. Not to mention a properly wired switch will show 120v across the screws when off
I'm not saying that is the problem, just saying it sounds like it would be worth checking. I've seen this mistake more than you might think and not always by DIYers.
 
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