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I am installing a new exhaust fan into my bathroom. I plan to use a 2 function rocker switch to operate the fan and light independently. The power passes through the light first, and then to the switch. Can anyone provide a diagram to help me complete the circuit from the light to the switch and to the exhaust fan? Thanks!

  • Have you run the wires already? Where are you on this planet? – ThreePhaseEel Jan 29 '18 at 4:47
  • ThreePhaseEel - location is bham, al. Wire was run in '73 when house was built. No complete attic access, but I can get wire to new fan from new switch. – Jason Smith Jan 30 '18 at 1:26
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The diagrams below show how to wire the circuit. For simplicity I have not drawn in the electrical grounding conductors (green or bare Cu wires).

Note that the 2011 NEC introduced a requirement to provide a grounded conductor at the switch location (see this answer and this outside link for more details). You can avoid this requirement if you install the circuit before January 1, 2020 but there are good reasons to follow the new code if it's not unduly burdensome. You may upgrade the switches in the future with a smart switch that requires a grounded wire. Or you may need to branch off this box in the future to run additional switched or unswitched circuits.

For a pre-2011 NEC 3-wire install the switch loop can be run using Type NM-B 14/3 with ground. Re-identify the white conductor in the switch loop cable as ungrounded (on both ends) and connect to the ungrounded conductor from the branch circuit. Then connect the black and red wires as indicated in the diagram.

For a 2011 NEC 4-wire install the switch loop could be run using Type NM-B 14/2/2 with ground. Connect the grounded (neutral) wire from the branch circuit to the white wire in the switch loop. Connect the ungrounded wire from the branch circuit to the white wire with red stripes. Connect the black and red wires as indicated in the diagram. As I write this, it is hard to find 14/2/2 cable and often more economical to run a pair of 14/3 cables. In each case we are running an grounded (neutral) wire inside the cable that has the ungrounded wires for each switch loop. This is required by code to avoid inductive heating.

Prior to 2011 NEC

2008 NEC Schematic

After 2011 NEC

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  • You'd use 14/4 instead of 14/2/2 for the post-2011 case – ThreePhaseEel Jan 29 '18 at 12:44
  • The cheap way is just to feed power to the switch first and then from there to the loads with that you only need /2. And for two loads switched from the same location you can use two /2 runs. Switch loops are false economy. – Dan D. Jan 29 '18 at 14:03
  • Just to clarify there are grounded and grounding conductors the grounded conductor is the neutral (usually white sometimes gray) and the grounding conductor is the green or bare copper. Many DIY folks don't understand that they are different and beyond the service panel they should not be connected (when they are connected it is referred to as a bootleg ground that can create a hazard). – Ed Beal Jan 29 '18 at 14:27
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    @DanD. I’m not sure if what you propose would adhere to NEC 300.3(B) req’t to keep all grounded and ungrounded conductors of the circuit in the same cable. – Stanwood Jan 29 '18 at 15:05
  • What I proposed would meet NEC 300.3(B), in fact that is of primary concern. But you are reading it to mean something it doesn't. It means that the ungrounded and their matching grounded conductors must enter and leave a box in a cable together. It does not mean that one can't branch out twice from one box and enter another twice. You just have to keep both pairs separate in the second box. Don't go connecting all the neutrals together. – Dan D. Jan 29 '18 at 15:52

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