What is the correct way to wire three way switches and a single pole switch?

Question

I have the above setup wired up. Here is a picture of the actual wiring of the right gang box.

But, the switches are clearly not wired correctly. What I am seeing when I test the switches is:

1 - the switch in the far left of my diagram

2 - the switch in the middle of my diagram

3 - the switch in the far right of my diagram

A - light on the left in my diagram

B - light on the right in my diagram

1	2	3	A	B
1Up	2Up	3Up	ON	ON
1Up	2Up	3Down	ON	off
1Up	2Down	3Up	off	off
1Up	2Down	3Down	off	off
1Down	2Up	3Up	off	off
1Down	2Up	3Down	off	off
1Down	2Down	3Up	ON	ON
1Down	2Down	3Down	ON	off

Looking at these results, light A is only on if the two 3-way switches are in the same configuration (both up or both down), regardless of how the single pole switch is configured. Light B is only on if the two 3-way switches are in the same configuration (both up or both down) AND the single pole switch is in the Up position.

I even climbed up into the attic to make sure there aren't any wires connecting the 2 lights. I can't figure out what in the world is causing these results. I especially can't understand how the second light (the one connected to the single pole switch) is being affected by the other switches.

Answer 1

Any color you want, as long as it's black.

- Henry Ford

No wonder you're confused. You have black wires doing 3 different functions. Let's grab our handy-dandy 5-pack of colored electrical tape, and re-mark the wires according to the job they are there to do.

• Black for always-hot
• White for neutral (required per Code)
• Red for switched-hot 1 (hot when you want that lamp 1 on)
• Blue for switched-hot 2 (hot when you want lamp 2 on)
• Yellow for the 2 travelers in a 3-way setup.

(standard 3-way diagram)

So let's re-mark the wires as needed with colored electrical tape. Now your drawing looks like this.

I only colored, I didn't change any wire routes... and so your drawing was completely correct. What went wrong is the confusion of black wires.

There is one special exception in wire marking. Your 3-way "spur" has white but it isn't neutral. In that case, white must be Always-Hot.* So, paradoxically, the white wire must be marked black** - and the black/red wires should be marked yellow.

Note that the use* and re-marking** of white wire black/always-hot is a Code requirement, not a Harper-ism. All other wire color markings are optional and are merely my suggestion.

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* Use white for always-hot: NEC 200.7(C)(1) sentence 3.

* Re-mark white: NEC 200.7(C)(1) sentence 1-2.

Answer 2

^{simulate this circuit – Schematic created using CircuitLab}

Figure 1. What you want.

^{simulate this circuit}

Figure 2. What you've got.

Answer 3

Your wiring diagram is in irreconcilable conflict with your truth table. I think your truth table is correct and your wiring diagram is wrong. Your circuit is actually wired like this:

As @Harper-ReinstateMonica has commented, you have mixed up the light-A cable with the power-in cable.

Power goes first to the common terminal of the near 3-way (switch 2), then via the travelers to the far 3-way (switch 1). The black wire in the 3-wire cable is not a constant-hot to switch 1, it is the switched-hot returned from switch 1.

You may find it hard to believe that you could have misdiagnosed your wiring this way, but this is one of those cases where you can stare at an error for days and not see it, while the first ignorant yahoo who comes along and looks over your shoulder points it out immediately.

You can verify this diagram by disconnecting the black wire from the common terminal of switch 2 and testing it for constant-hot.

Once you have correctly identified all the cables and wires, you should have no trouble connecting everything up according to the diagram in your question, which, as you have maintained all along, should work properly.

And you don't need to run any more 70-foot wires.