Confused about Light/Switch wiring in existing home...

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Old 04-16-16, 01:19 PM
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Confused about Light/Switch wiring in existing home...

I'm trying to learn more about wiring in my house due to a couple of changes I want to make and a general interest as a DIY'er. My house was probably wired around 1970.

The light in my Bedroom has through-power at the Junction Box and a switch wired for the light. I've got two white leads? One is the Neutral white cluster and the other is the white of the switch wire going to the bottom of the switch?
The black from the top of the switch is wired directly to the power source at said Junction Box.

I'm confused because I thought the white lead from the bottom of the switch is supposed to connect up to the Hot black grouping and the black from the switch should go directly to the light -- with the white from power source directly to the light.

Yet I checked my other upstairs bedroom and that is the way it is wired and works.

Thanks for any help understanding what is going on here!

I had forgot after pulling the light out, and after my recent studies this looks weird!

I thought it would work backwards this way with the switch turning on in down position.

If you look closely in the picture you can see the white lead instead of what I thought was supposed to be a black lead for connection to the light fixture..

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Last edited by plumsmooth; 04-16-16 at 01:38 PM.
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Old 04-16-16, 01:27 PM
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I thought the white lead from the bottom of the switch
Top and bottom are meaningless when talking about a standard SPST switch. The terminals are interchangeable.
I thought the white lead from the bottom of the switch is supposed to connect up to the Hot black grouping and the black from the switch should go directly to the light
That is standard wiring convention to avoid confusion because most installers do not remark the white as an ungrounded conductor* but electrically it doesn't matter.

*Code requires the white to be remarked when used as an ungrounded conductor but it often isn't done.
 
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Old 04-16-16, 01:29 PM
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Disregard. Reply in progress. I type too slowly.
 
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Old 04-16-16, 03:38 PM
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less complicated version

Light Switch Wiring Power into Box...

White from Power Source to Light, Black from Power source to Black at Top of Switch, White from Bottom of Switch to Light

or

White From Power Source to Light, Black from Power Source to White and Bottom of Switch, Black from Top of Switch to Light.

Each one creates a circuit. Light works either way up/down normal?
 
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Old 04-16-16, 04:05 PM
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White From Power Source to Light, Black from Power Source to White and Bottom of Switch, Black from Top of Switch to Light.
That would be the normal way to do it but as far as I know it isn't a code requirement just beast practice.
Light works either way up/down normal?
If you mean the switch turns the light on and off connected either way, yes. A single pole single throw switch is "color blind".
 
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Old 04-16-16, 04:34 PM
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Thanks I think I get it...

The color coding principle has "thrown" me a bit.

But now understanding that the SPST-switch wire location -- top and bottom respectively means nothing.

Combine that with no color coding in my light/switch configuration and the situation is most likely under control...

White goes to the light!

Without color coding, the black wire from the power source just stayed a black wire to the top of the switch. But it could have gone to the bottom right?

And the white wire from the bottom of the switch went back to the light Hence two white leads to my light...
 
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Old 04-16-16, 04:58 PM
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Without color coding, the black wire from the power source just stayed a black wire to the top of the switch. But it could have gone to the bottom right?
Correct.

Usually we change the color of the white wire so it's not confused as a neutral. I like to remark it with blue tape but even a Sharpie marker works.
 
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Old 04-16-16, 05:53 PM
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It works either way.

But the rule is that you may not have both of the wires going to the light socket being white. So you need to exchange the switch wires up at the light fixture so the black from the switch goes to the light fixture black lead (or the light fixture darker colored terminal screw) and the other wire from the switch goes to the power cluster of blacks.

In addition, both ends of the white wire going to the switch must still be marked with colored (not green) tape or stain. Long ago, this last rule was not always the case because a white wire connected to a switch terminal or to colored wires is not to be considered a neutral.

Oh, by the way, whether the switch is "on" with the toggle up or "on" with the toggle down depends on the physical position of the switch in the box, not which wire is connected to which terminal.
 

Last edited by AllanJ; 04-16-16 at 06:09 PM.
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