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Old 06-15-2010, 06:58 PM   #1
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"switch loop" wiring questions


Ive noticed my house is wired with the "switch loop". I want to know if someone can show me some diagram of how the "switch loop" wiring works. I dont understand the concept of the wiring. I cant find a diagram on the internet.

When i went to change a light, i turned off the switch, went to take out the light, before unscrewing the marettes i took my voltage detector and it beeped. So i turned of the breaker and unhooked it. Im used to seeing one set of wires in the ceiling box, but not two sets of wire. Im confused on the concept of how the wiring works.

Does the power go through the black wires in the ceiling box down to the switch, then when the switch turns on, the red wire sends the power to the light??

I'll briefly describe how one set of my lights are wired.

In the ceiling box theirs a 14-2 and 14-3. Theirs 2 black wires spliced together, theirs 2 whites and the white from the light spliced together, and the red from the 14-3 is spliced with the black from the light. The light switch has the black and red wire wired, the white is connected with another white in the box.

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Old 06-15-2010, 07:09 PM   #2
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"switch loop" wiring questions


Not hard to describe. The wire from the panel is actually up in the junction box, not at the switch. From there, you have a length of wire that interconnects between the Black "hot". Thus a "Switch Loop". There is actually diagrams on here and in Black & Decker's book on wiring.

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Old 06-15-2010, 07:13 PM   #3
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"switch loop" wiring questions


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Originally Posted by gregzoll View Post
There is actually diagrams on here and in Black & Decker's book on wiring.
Their's diagrams on the diychatroom??what would the name of the diagram be??
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Old 06-15-2010, 07:14 PM   #4
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"switch loop" wiring questions


YOur description is one way it works if there is a three wire cable used. If only a black and white wire cable is used then power goes to the switch on the white wire and comes back on the black wire.
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Old 06-15-2010, 07:18 PM   #5
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"switch loop" wiring questions


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YOur description is one way it works if there is a three wire cable used. If only a black and white wire cable is used then power goes to the switch on the white wire and comes back on the black wire.
The ceiling box has a set of black/white/ground wire. And another set of black/red/white/ground wire. The switch is wired with the black and red on the switch, the white is connected with another white.
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Old 06-15-2010, 07:49 PM   #6
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"switch loop" wiring questions


Given your setup the circuit is being continued somewhere else using the black and white. The red is just a switched hot back to the fixture box.
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Old 06-15-2010, 09:05 PM   #7
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"switch loop" wiring questions


Evolution of the switch loop.

Normally the white neutral follows the hot wire everywhere. But to avoid wasted wire, when the power enters at the light fixture, we don't have the neutral follow the hot down to a switch and back.



For premade cables (like Romex) but not individually strung wires in conduit, the white wire may be used for the raw power down to the switch using a switch loop when no other colored wire is available. A white wire in such a hot role must be marked with colored (not green) tape or stain at both ends.

For diagram 3 it doesn't matter whether the red between the switch and the fixture is used for the switch loop return or for the hot feed that also continues beyond the switch.
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Last edited by AllanJ; 06-15-2010 at 09:15 PM.
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Old 06-16-2010, 11:04 AM   #8
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"switch loop" wiring questions


thanks for your answers, i understand the concept now.

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