# Does it matter where power source is introduced in a three-way circuit?

I am in the process of replacing a single stairway light with a series of three lights (spaced apart). The previous setup included two switches and one light. One of the switches at the bottom of the stairs and one at the top of the stairs.

The two switches are connected with 12-3 (I tested continuity with a long wire). The power source was wired into the light along with wiring from the top switch.

When installing my three lights, I roughly followed the diagram directly below. My one deviation is that the power is introduced at the second light of the circuit and not the first.

Below is another diagram I created that is more accurate to my exact setup. As you can see in the diagram, I am getting light to the middle and lower lights, but not to the top light.

This brings me to my question: Does it matter where power source is introduced in a three-way circuit?

Edit #1 – Updated Diagram

Edit #2 – Updated Diagram of Potential Solution What if I keep the existing /2 cable going to all of the lamps and instead splice into the existing power source (inside a junction box) and run the now longer power source to the switch at the top of the stairs? Below is a diagram – I think I have everything connected properly.

Edit #3 – The solution proposed directly above (and depicted directly below) worked.

• Yes, it matters. But you need to show us a more complete drawing of what you've actually done, without handwaving away the details - because the details matter. Please Edit your question with more info. Commented Mar 13, 2022 at 23:00
• If you have existing wiring to work with it matters. If installing new you can place the feeder at any location, the easiest method for new wiring is to use “Smurf tube” it is a flexible nonmetallic conduit that you put the wires you want in and save \$\$ over X-2-2 with ground. Commented Mar 13, 2022 at 23:21
• Per last diagram, there's no neutral at the light that does not light, so no surprise it does not light. You need a 12/3 to the right of that to the power supply. You are evidently connecting it between switched hot and hot. Commented Mar 14, 2022 at 1:01

3-way circuits work like this. Note the 2 travelers.

Black = always-hot
Red = switched-hot
Yellow = travelers
White = neutral
Grounds not shown.

Now when the 3-way group is on the end like that, you can treat the group like 1 simple switch that either connects always-hot to switched-hot, or does not.

So now the question is, "how do we wire several lamps when the switch is at the end, and power comes into a middle lamp?" The same way we wire any other supply-switch-lamp arrangement:

• Always-hot goes from power supply to the switch.
• Switched-hot from the switch to every lamp.
• Neutral goes from power supply to every lamp. And the switch.*

Go ahead and draw this out, each wire in turn.

You will see that you needed /3 cable from power supply to lamp 1, and from lamp 1 to switch.

I'm sorry you didn't put it in there and you have to fish the correct cables in there, or bust up drywall. I would bill that website.

This sort of problem can sometimes be corrected with smart switches, but I don't see a way here, unless you wire the bulbs to be on 24x7 and use smart switches talking to smart bulbs.

You just pinched the pennies a little bit too hard by trying to get it done with /2 cable and not researching or testing before the drywall went back up.

* As per NEC 404.2(C) which took effect in NEC 2011. That wiring diagram you linked is wrong, and ignores this decade-old requirement - no excuse. Given the source, I am not surprised. Many people have yelled at them about their wrong diagrams, but they either will not relent, or these are secondhand or thirdhand copies. I would bill them for the rework.

• Thank you for the educational breakdown. I have updated the post with a proposed solution. Thoughts? Commented Mar 15, 2022 at 22:38

You've identified a difference between the two diagrams, but it's not the important difference. The important thing is that the switch loop needs to be present in the same junction box as the power source.

Look at the first diagram closely. See how the incoming black hot wire is connected to the white wire going into the switch loop, then the black wire ("switched hot") returning from the switch loop connects to the black wire feeding all the lights? That's what I'm referring to when I say the switch loop and the power source are present in the same box.

The wiring of the second diagram can be corrected in one of two ways: re-route the 12/2 switch loop cable or the 12/2 power source cable so that they both arrive into the same box, or else use 12/3 cable for the stretch between the two boxes. (If this were done in conduit rather than NM cable, one could pull another single conductor into the conduit.)

If the walls are open so that cable can be easily re-routed you really should make arrangements so that a neutral is available in both of the switch boxes. Current electrical code requires this so that (for example) there's a neutral available for powering smart light switches.

• Unfortunately, the walls are not open. I cut a channel from the top switch to the three lights and guided the 12-2 through holes in the studs. The bottom switch would be tougher to access as access would be below subfloor. Editing the post in a minute with an updated diagram for clarity. Commented Mar 14, 2022 at 0:20