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Old 01-18-2009, 04:14 PM   #1
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Black or white to switch outside the main run?


I have looked through NEC, but have not found anything that specifies how to install a light switch a certain way. Look at http://www.doityourself.com/stry/h2installswitch under "INSTALLING SWITCH OUTSIDE MAIN WIRING RUN" for a diagram of what I am talking about. Intuitively, there are 2 ways to do this.

1) You can connect the black(hot) from the source to the wire going to the switch, and the other wire from the switch to the light. This is how this page says to do it, and how I have always seen it done.

2) You could instead connect the white (neutral) from the source to the wire going to the switch, and the other wire from the switch to the light. I haven't seen this done, but am surprised this is not slightly preferred for safety, since less wire is attached to power when the light is off.

Just curious why #1 is the standard, and what NEC has to say about this if anything.

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Old 01-18-2009, 05:16 PM   #2
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Black or white to switch outside the main run?


Think of the switch in a loop water system. Water flows past the bulb, through the switch, but if the valve is closed, it does not flow back to the other end, which is when a switch is off. When the switch is on, which is like a valve that is open, then the water flows through, past the bulb, and exits out of the pipe at the other end.

What you are looking at is esentially what I described. Power comes into the light, Black on one side, White goes to the Switch Black leg, with Return back as White from the Switch to the other side of the light.

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Old 01-18-2009, 05:30 PM   #3
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Black or white to switch outside the main run?


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Originally Posted by gregzoll View Post
What you are looking at is esentially what I described. Power comes into the light, the Black continues to the switch, with the return back on the white. The white at the switch is connected to the light, with the other white for power connected to the other side of the light You turn off the switch, and stop the flow. When you run power to the switch first, the Blacks connect to the switch, but White continues to the light, which they are tied together.
Greg,

Using the white as the switched return to the light is prohibited by the code. The white can only be used as the supply to the switch. The NEC has also added an article that addresses re-identifying the white as it is not a neutral.

Using your procedure above both the wires connected to the fixture would be white.
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Old 01-18-2009, 05:34 PM   #4
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Black or white to switch outside the main run?


I think that I fixed it. I did not notice it until I went back to reread what I had posted. This is why I always hated Switch Legs, and never did like them in the Navy.

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Old 01-18-2009, 05:47 PM   #5
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Black or white to switch outside the main run?


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What you are looking at is esentially what I described. Power comes into the light, Black on one side, White goes to the Switch Black leg, with Return back as White from the Switch to the other side of the light.
Power comes into the light. White from ceiling goes to white from fixture. Black from ceiling to white going to the switch. Return back as black from the Switch to the black on the fixture.

Both ends of the white used in the switch loop should be re-identified by a color other than white or green. I use a black, red or blue sharpie marker.
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Old 01-18-2009, 06:39 PM   #6
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Black or white to switch outside the main run?


I want to clarify, I am not asking how to wire this or how it works. I am asking why people do it this way, instead of running the neutral to/from the switch.
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Old 01-18-2009, 06:48 PM   #7
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Black or white to switch outside the main run?


Nobody except stupid people switch the neutral. I would like to see what happens when you switch the neutral on a MWBC....
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Old 01-18-2009, 06:48 PM   #8
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Black or white to switch outside the main run?


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I want to clarify, I am not asking how to wire this or how it works. I am asking why people do it this way, instead of running the neutral to/from the switch.
The switch does not need a neutral so there is no need to run it to the switch. This saves on materials and cuts down on box fill. Often times it is just the way that the boxes are laid out.
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Old 01-18-2009, 07:50 PM   #9
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Black or white to switch outside the main run?


That is because who ever designed that site did it wrong. Even when I first typed it out, until pointed out that I stated the hook up incorrectly, I had to go back and edit.
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Old 01-18-2009, 09:23 PM   #10
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Black or white to switch outside the main run?


Guys, the OP is asking why we switch the hot instead of the neutral, not about wire colors.

The reason is because the fixture would still be live, but appear to not be. We never switch the neutral unless we switch the hot at the same time.
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Old 01-18-2009, 10:46 PM   #11
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Black or white to switch outside the main run?


Thanks InPhase277, that makes sense.

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