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Discussion Starter · #1 ·
So I go over a property that belongs to a friend (rental) because the tenant was complaining about the bathroom gfi not working. So I get in there and it's one of those gfi, switch combos. The switch controls the vanity light and is operational. I pull out the device to find one piece of 2 wire romex (old cloth kind) coming into the box. My first thought is the switching is being done either in a hidden j box in the wall or the fixture box for the vanity light and some idiot threw in the gfi combo deal to satisfy an inspector that never bothered to test an outlet. I wish I could remember the exact configuration of the wiring on the device but I can't. I know the ground was connected to the neutral screw and the white wire to the hot screw of the gfci, and the black wire to one of the little wires that comes out at the top. Just to make sure of my theory I do a continuity on the black and white wires, and my thoughts are confirmed. So then I test voltage between black and white and I get 120!????? So I pull the light off and it appears to be what I think with the power coming into the fixture box, going down the black and coming back on the white to the light. So I began to investigate further into this box (there were more splices) but the tenant starting raising hell (it was late, I came after work) so i put the light back, installed a regular switch and told them I'd be back on Monday. So I'm thinking a back feed issue but still I'm confused how across the 2 wires is 120 yet I put them together and the light turns on. Any ideas??
 

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Mad as Hell Member
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When you tested for voltage between your white and black, was the light fixture still in the circuit?

You could be reading through the filament and picking up the neutral. Giving you around 120, probably a little less depending on exactly what type of lamp was installed.
 

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You are reading through the fixture. The voltage reading you are getting is exactly what I would expect you to read across an open circuit (ie. open switch). You do not have a problem, your readings are normal. It sounds like the only issue you have is the non working gfci due to not having a neutral in the switch box.
 

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Flex Bits & Blindfolds
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It sounds like a switched neutral. The hot is feeding the fixture with constant power, the neutral goes through the switch and to the fixture. So, the hot is going through the fixture, through the filament on the bulbs and back through the neutral wire that is at the switch. The other wire at the switch is connected to the neutral bar. If you pull the bulbs and retest the two wires at the switch you won't get 120, it will be dead.
Bank on it
 

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Flex Bits & Blindfolds
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So you could have answered this your first year in?

Thank you for explaining
No he couldn't, but he is going to tell you you should have your journeyman there. My advise to you, ignore him, keep learning, and asking questions. He undoubtedly learned the same way, by trying and asking.
 

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Mad as Hell Member
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MTW thinks he's God's gift to the trade ever since he got out of residential and started as a labourer with an industrial shop.

He still isn't running work or doing any of the big boy jobs. But he's always around to snap a picture or two, until his dad tells him to get back to work.

His biggest accomplishment in the trade is maintaining a 14 post per day average on Electriciantalk.com
 

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Discussion Starter · #14 ·
When thought out this is really quite simple. And I'm fine with a little ball busting, I don't take myself that seriously.
 

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MTW thinks he's God's gift to the trade ever since he got out of residential and started as a labourer with an industrial shop.

He still isn't running work or doing any of the big boy jobs. But he's always around to snap a picture or two, until his dad tells him to get back to work.

His biggest accomplishment in the trade is maintaining a 14 post per day average on Electriciantalk.com
You couldn't wire a single pole switch if your life depended on it.
 

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So you could have answered this your first year in?

The rest of you guys thanks for explaining
Im sure he was thinking about electricity before he even got into the trade. Hes flippin brilliant.

Anyway, are you reading this with a high impedance meter? Try a wiggy, also watch the lights.
 
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