2011 NEC – 3 Way – Power Source and Fixture Feed at Different Switch

You will need…

1. A 3 wire cable that is routed between switch box 1 and switch box 2 – these wire cables comes with a black / red / white wire plus the bare equipment grounding wire.
2. A 2 wire cable that is routed between switch box 2 and the fixture box – this wire cable comes with a black / white wire plus the bare equipment grounding wire.
3. A circuit power supply source wire cable that is feed to the switch 1 box.
4. Insulated wire nuts to connect / join wire together, variety of sizes out there so make sure you obtain the correct size.
5. Wire staples, to affix the wire cables to wall studs as needed. Wire cable must be secured within 6 inches of entering the electrical box.
6. Wire cable / wire strippers.
7. Screwdrivers as required.

Holes drilled to feed wires through studs must be 1 1/4″ from edge of stud, in instances where the wire cable is closer then the edge of stud must have a 1/16-in. thick protective metal plate over the area where the cable is being feed through (may want to notch the stud so that that the protective plate does not create a bump on the drywall). Also read the article called ‘Wire Routing Basics’

Wire cables entering the electrical box – secure the cable clamp at the box snug enough that the cable cannot come out but not too tight as to pinch the cable and break through the insulated cover of the cable.

You must have at least 6 inch length of wire inside the electrical box, it can be a bit more but not less, it can fail an inspection if the length of each wire is less than 6 inches. Also read the article called ‘Box Fill Calculations’ as there is a limit on how many wires are allowed for a certain size electrical box.

STEP 1 – Make certain that the power supply cable is dead – turn off the electrical breaker at the service panel. Make certain that everyone in the house is aware of what you are doing so that they do not get the notion to reset the breaker when another light in the home is not working.

STEP 2 – Make the box openings (if a existing home)

STEP 3 – Feed / Route the wire cables.

STEP 4 -Mount / Install the Electrical Boxes (make sure the electrical boxes are secured as some fixtures are heavy and may require additional support) [The electrical box should not extend beyond the edge of the finished wall or ceiling so that the fixture can mount flush to the ceiling and the wall switch cover will mount flush – but it also should not be recessed too far into the wall or ceiling]; then feed the wire cables into the electrical boxes. Sometimes because of tight openings in existing homes, the wire cable may to be feed into the electrical box then the box put in position and secured.

STEP 5 – Connect the wires…

Connections Instructions:

At the Fixture box…

One cable entering this box coming from switch 2.

• a) connect the white wire to the grounded conductor (neutral) of fixture – if screw type connections then connect to the silver color screw.
• b) connect the black wire to the switched ungrounded conductor (hot) of fixture – if screw type connections then connect to the brass color screw.
• c) please see under important notes in regards to the equipment grounding conductor (bare wire).

At switch 1 box…

Two cables entering this box, one is the circuit power supply cable, one cable coming from switch 2.

• a) using an insulated wire nut connect / join the white wire coming from the ‘circuit power supply cable’ + the white wire coming from switch 2.
• b) connect the black wire coming from the ‘circuit power supply cable to the common screw of switch 1.
• c) connect the red wire coming from switch 2 to the one of the remaining main screws of switch 1.
• d) connect the black wire coming from switch 2 to the last remaining main screw of switch 1.
  *e) please see under important notes in regards to the equipment grounding conductor (bare wire).

At switch 2 box…

Two cables entering this box, one cable coming from switch 1 and one cable coming from the fixture.

• a) connect the black wire coming from fixture to the common screw of switch 2.
• b) using an insulated wire nut connect / join the white wire coming from switch 1 + the white wire coming from fixture.
• c) connect the red wire coming from switch 1 to one of the remaining main screws of switch 2.
• d) connect the black wire coming from switch one to the last remaining main screw of switch 2
• e) please see under important notes in regards to the equipment grounding conductor (bare wire).

Important Notes:

By electrical codes you MUST have at least 6 inches of wire in the electrical box itself, and also the wire must be able to reach at least 3 inches outside the box, it can fail an electrical inspection if the required min. wire length is not met. You may have the wires a bit longer (within reason) but they cannot be shorter. Also see the note on box fill further down in this article.

If the fixture has screw type connectors, the switched ungrounded conductor (hot) is connected to the brass color screw, and the grounded conductor (neutral) is connected to the silver color screw. If it has black and white wires coming from fixture, then just connect black to black and white to white. Use wire nuts of the correct size to join wires together.

The wire cable running between switch 1 and switch 2 has 3 wires in it – black / red / white (plus the bare equipment grounding wire)
What is not shown in the drawings to avoid confusion, is that each wire cable also has a bare equipment grounding wire included. This wire is connected to a grounding screw in each electrical box (if the box is metal), joined either through the grounding screws in the box itself or via a wire nut to the bare wire of the next cable entering / exiting the box, it is also connected to any grounding screw (if there is one) on the switch itself, as well as any grounding screw at the fixture (green wires that attach to the fixture are grounds). Now if using a plastic box, it is made of a material that is non conductive, however some plastic boxes have a metal strip inside that can still be used to connect equipment grounding wires, in the event that it does not use wire nuts to join the bare grounding wires together. The equipment grounding wire (bare in most cables) must be electrical conductively joined throughout the circuit. Green wires are also equipment grounding conductors.

At the switch itself there are 3 main electrical screws, one of these 3 screws is distinctly different in color (perhaps darker) than the other 2. This screw connection is called the common screw. It is very important that in order for the 2 switches to work as they are intended to that the correct wire is attached to the common screw. Basically as depicted in the drawings one switch has the ungrounded conductor (hot) from the circuit power supply cable attached to the common screw, where the other switch had the ungrounded conductor (hot) feed to the light fixture itself.

Please also note that there are a variety of manufactures out there that make 3 way switches so it is possible that the switch you buy may have the common screw located in a different spot or side of the switch then depicted in the drawings in this article, just make sure that the wire depicted to go to the common screw of each of the switches is actually connected to the common screw of the 3 way switch you bought. The other 2 wires going between the remaining screws of one switch to the other switch does not matter as long as one wire of the 2 remaining wires go on each of the remaining 2 screws of the screw.

If there is an equipment grounding screw on the 3 way switch it may be green in color and be separated away from the main connections of the switch and likely part of the metal frame that is also part of the mounting structure of the switch.

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Extensions to this Switch circuit…

Be Aware that there is a limit by code on how many wires can be in a given size electrical box, when adding more wires to the same box you may have to install a larger and / or deeper box to allow space for more wires coming and out of the box.

Here is an article / explanation in regards to box fill calculations ‘Box Fill Calculation’

The instructions here are based on the fact that the circuit has already been wired to the configuration shown in this article and we are now making the wiring changes for onward power.

From the switch locations….

Only always on power is available from the switch 1 location. Switch 2 only has onward switched power available.

Switch 1 options…

Onward Always On Circuit Power…

(showing bellow the switch portion of the circuit)

Not shown in the diagram but the onward cable also has a bare wire (equipment grounding conductor) that also must be connected to all the other bare wires at the switch electrical box.

Connection Instructions for onward cable (always on)

• a) Using an insulated wire nut, attach / join – the white wire of onward cable + the white wire from ‘circuit power supply cable’ + the white wire coming from switch 2.
• b) Using an insulated wire nut, attach / join – the black wire of onward cable + black wire connected to the common screw of switch 1 + the black wire coming from ‘circuit power supply cable’.

Identification of wires in onward cable….

Black – Ungrounded conductor (hot – always on)
White – Grounded conductor (neutral)

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Switch 2 options…

Onward switched power…

(example more than one light fixture controlled by the same 3 way switches)
(showing bellow the switch portion of the circuit)

Not shown in the diagram but the onward cable also has a bare wire (equipment grounding conductor) that also must be connected to all the other bare wires at the switch electrical box.

Connection Instructions for onward cable (switched)

• a) Using an insulated wire nut, attach / join – the white wire of onward cable + the white wire coming from fixture + the white wire coming from switch 1.
• b) Using an insulated wire nut, attach / join – the black wire of onward cable + the black wire connected to common screw of switch 2 + the black wire coming from fixture.

Identification of wires in onward cable….

Black – Switched ungrounded conductor (hot – switched)
White – Grounded conductor (neutral)

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From the fixture location…

At the fixture location only switched onward power is available.
(example more than one light fixture controlled by the same 3 way switches)
(showing bellow the fixture portion of the circuit)

Not shown in the diagram but the onward cable also has a bare wire (equipment grounding conductor) that also must be connected to all the other bare wires at the fixture electrical box.

Connection Instructions for onward cable (switched)

• a) Using an insulated wire nut, attach / join – the white wire of onward cable + the white wire connected to the grounded conductor (neutral) of fixture + the white wire coming from switch 2.
• b) Using an insulated wire nut, attach / join – the black wire of onward cable + the black wire coming from switch 2 + the black wire connected to the switched ungrounded conductor (hot) of fixture.

Identification of wires in onward cable….

Black – Switched ungrounded conductor (hot – switched)
White – Grounded conductor (neutral)

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Foreign Users:

The colors of the wires depicted are based on the standards and code requirements / configuration in the United States and Canada. If you are viewing this site from a foreign country, your wiring standards and color of wires may be different but the principal and sequence of wiring will still remain the same. Therefore the information in this article may still be of use to you regardless of what country you may be in. Just translate the colors used here to the color of wires used in your country in regards to ungrounded (hot) conductors / grounded conductors (neutral) and equipment grounding conductors as well know applicable code requirements in your country.

WHILE EXTREME CARE HAS BEEN IMPLEMENTED IN THE PREPARATION OF THIS SELF-HELP DOCUMENT, THE AUTHOR AND/OR PROVIDERS OF THIS DOCUMENT ASSUMES NO RESPONSIBILITY FOR ERRORS OR OMISSIONS, NOR IS ANY LIABILITY ASSUMED FROM THE USE OF THE INFORMATION, CONTAINED IN THIS DOCUMENT, BY THE AUTHOR and / OR PROVIDER.

By: Donald Kerr