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I currently have a bathroom light and a single pole switch at the door. The power for the light first comes into the ceiling box directly above the light. The hot is tapped in right there by using the white wire of 14/2, said 14/2 then runs to the switch where both the white and black are used to run through the switch and then back to the light with now the black wire hot with switch on.

Now I'm putting in a light that has a vent fan attached. I will be installing a 2 function switch instead of the single pole so I can control the fan and the light separately. So, I'm thinking, why not just replace the 14/2 that runs through the switch now with 14/3 wire. I can do that in the attic. I'll use the white from said 14/3 to carry the hot to my switch securing on the the black switch screws (and not break off the tab). I'll then hook up the black and red from the 14/3 on the other side of the receptacle so they carry the power back to the fan or light. I will put black tape on white wires to designate hot.

  • Why do you want to use 14/3 instead of 14/4 here? – ThreePhaseEel Jan 30 at 23:55
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It's better (and to code for new construction) to run a 14/4 wire to get a neutral to the switch. In case you want to upgrade it to a smart switch or timer that needs that neutral.

You could leave the 14/2 in place as the unswitched feed and run a new 14/3 in parallel to carry the switched lives. However when you do so you must ensure that the neutral goes back to the through that 14/3 and that the lamp/fan is connected to that neutral and not the one feeding the 14/2.

  • I didn't know there was such a thing as 14/4. Good info. I'm hesitant to add yet another cable above the light, as there are 3 there now (one feeds vanity light) and I don't know how much space the wire box on the new fan/light combo will have. – Bob Jan 30 at 16:39
  • As long as it remains accessible from the attic you can add a junction box upstream in the run to T off to the vanity to reduce the fill in the fan/light box – ratchet freak Jan 30 at 16:54
  • Now you got me thinking. I'll do this right. I can easily reach the existing junction box that feeds power to the light box. I"ll remove that feed to the light box, and install a new 14/2 from that junction box and route it to the switch as power supply. Then I'll just replace the existing 14/2 that goes to the switch from the light with 14/3. Thank you for your help. – Bob Jan 30 at 17:18
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    I don't believe you can parallel two separate cables for the added conductor, that violates a basic rule of currents being equal amongst all conductors in a cable or conduit. However, because of the ease of cable replacement, i.e. Without removing any drywall, a neutral is not required at the switch. – Harper Jan 30 at 20:01
  • @Harper -- it's the box that needs to be exposed for the 404.2(C) point 2 exemption to apply – ThreePhaseEel Feb 1 at 0:24
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No, it can't be, not in your situation at least

NEC 404.2(C) is where the requirement for neutrals (grounded circuit conductors) at light switches is located:

(C) Switches Controlling Lighting Loads. The grounded circuit conductor for the controlled lighting circuit shall be installed at the location where switches control lighting loads that are supplied by a grounded general-purpose branch circuit serving bathrooms, hallways, stairways, or rooms suitable for human habitation or occupancy as defined in the applicable building code. Where multiple switch locations control the same lighting load such that the entire floor area of the room or space is visible from the single or combined switch locations, the grounded circuit conductor shall only be required at one location. A grounded conductor shall not be required to be installed at lighting switch locations under any of the following conditions:

(1) Where conductors enter the box enclosing the switch through a raceway, provided that the raceway is large enough for all contained conductors, including a grounded conductor

(2) Where the box enclosing the switch is accessible for the installation of an additional or replacement cable without removing finish materials

(3) Where snap switches with integral enclosures comply with 300.15(E)

(4) Where lighting in the area is controlled by automatic means

(5) Where a switch controls a receptacle load

The grounded conductor shall be extended to any switch location as necessary and shall be connected to switching devices that require line-to-neutral voltage to operate the electronics of the switch in the standby mode and shall meet the requirements of 404.22.

Exception: The connection requirement shall become effective on January 1, 2020. It shall not apply to replacement or retrofit switches installed in locations prior to local adoption of 404.2(C) and where the grounded conductor cannot be extended without removing finish materials. The number of electronic lighting control switches on a branch circuit shall not exceed five, and the number connected to any feeder on the load side of a system or main bonding jumper shall not exceed 25. For the purpose of this exception, a neutral busbar, in compliance with 200.2(B) and to which a main or system bonding jumper is connected shall not be limited as to the number of electronic lighting control switches connected.

Informational Note: The provision for a (future) grounded conductor is to complete a circuit path for electronic lighting control devices.

For your case specifically, since the box the switch is housed in is installed into finish materials, 404.2(C) point 2's exemption does not apply to your situation, which means you'll need to go get some 14/4 and put it in if you want a switch loop there, with the black as always hot, red and blue as the switched-hots, white as neutral, and bare as ground. Since you're using "dumb"/"steam" switches (vs. "smart" switches), the neutral simply gets capped off.

Of course, ratchet freak's alternative of running a 14/2 down to the switch for power and a 14/3 back up with the switched-hots and neutral works, provided you can keep your neutrals straight in the light box that is, which is why a single-cable approach is typically preferred here.

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There is 14/4 (white, black, red and blue) usually used for smoke alarm interconnect, but not necessary in this situation. Use 14/3 from ceiling junction box to tandem (twin) wall switches; one wire (lets pick white, to carry the power from the ceiling box to both switches. Pigtail this white wire with two short pieces of black wire inside the switch box on the wall. Give power to both switches with these short black wires. Tape both ends of the white wire with black tape to identify as HOT conductors. Now you can power the fan and the light independently with their own switches. Use black and red wires to give switched power back to the individual devices on the ceiling. This is known as a switch loop, actually its two switch loops. That being said there is a new code requirment in the U.S. that I am not familiar with. I'm in Canada.

  • He will need 14/4 for this.... – ThreePhaseEel Feb 1 at 0:17
  • Why will he need 14/4? – Chris Taylor Feb 1 at 4:48
  • See the Code reference in my answer – ThreePhaseEel Feb 1 at 12:37

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