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Old 11-15-2009, 08:12 AM   #1
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Switch Question


Hopefully quick, easy questions:

I've just moved into a new house (built 1990) and found a bedroom with a switch that does not appear to do anything - doesn't turn on a light, doesn't power an outlet (or at least in that room).

I wanted to use the switch to add a light fixture, but found the multimeter shows a voltage of 0V from black to neutral, but 120V from black to ground, or 120V white to ground. So both are hot.

So questions - is the hot white ok? and if so, do I install, treating it as though white were neutral?

Thanks for any help

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Old 11-15-2009, 08:15 AM   #2
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Switch Question


How many cables go into this light switch?

If it's only 1 cable - black/white/ground then it is a switched loop
Both white & black will be hot when it is on

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Old 11-15-2009, 08:16 AM   #3
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Switch Question


There is just one cable into the box. black, white and ground.
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Old 11-15-2009, 08:29 AM   #4
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Switch Question


Then most likely you do not have a hot/neutral/ground
--unless it was an outlet & someone removed the outlet to put a switch in

Did you test for power with the switch off?
Switch on both will be hot
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Old 11-15-2009, 08:38 AM   #5
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Switch Question


I actually ended up disconnecting the switch entirely and testing.

White / Black are both hot. Show 0V to each other, and each shows 120V to ground.
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Old 11-15-2009, 08:41 AM   #6
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Switch Question


Quote:
Originally Posted by gordseskimopie View Post
White / Black are both hot. Show 0V to each other, and each shows 120V to ground.
Put a 100w incand. bulb across your voltmeter and remeasure.
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Old 11-15-2009, 09:04 AM   #7
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Switch Question


It's a switch loop. The power is a the source of the cable. There is no neutral.
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Old 11-15-2009, 01:25 PM   #8
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Switch Question


I'm trying to get the consensus here... With a switched loop, I've read on other sites that it's a hazard, but a very minor one - I take it as most would go ahead with the install, rather than make a significant effort to rewire.
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Old 11-15-2009, 02:14 PM   #9
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Switch Question


The switch loop likely comes from a receptacle that is supposed to be half switched but they didn't break the tab (between the brass colored screw terminals on the hot side of the recep).

To use this switch to power a ceiling light fixture you must find the receptacle in question are rewire it.

One of the receps in the room will have the white tied to a black. If you change this to black/black, white/white, you will have a hot and a nuetral in the sw box.
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Old 11-15-2009, 03:51 PM   #10
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Switch Question


I think I could figure out which receptacles are on this circuit by just shutting off and testing the reasonable areas. But how do I know which of the receptacles would be the one that should have the tab broken?
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Old 11-15-2009, 05:47 PM   #11
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Switch Question


Look for a white and black tied together in the receptacle to find the one that should have the tab broken. If there are any red wires in the receptacle boxes then there could be more than one switched receptacle.
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Last edited by joed; 11-15-2009 at 05:51 PM.
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Old 11-15-2009, 07:55 PM   #12
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Switch Question


Quote:
Originally Posted by gordseskimopie View Post
I think I could figure out which receptacles are on this circuit by just shutting off and testing the reasonable areas. But how do I know which of the receptacles would be the one that should have the tab broken?
We must do some good old fashioned leg work (or brain work). After all the great advice you've gotten from joed and 220/221, all that's left is to find the receptacle whose tabs are to be broken; The one that has both the black and white wires on the HOT side, in addition to the supply wires. (No matter what) Don't drink and Drive, Ever!!!
p.s.: The devil (can't bring up that icon) is in the details:
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Old 11-15-2009, 09:27 PM   #13
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Switch Question


for sure.. great help here. Thanks to all, very much appreciated.

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