My husband and I recently decided to build a small pantry closet in our kitchen/dining room area. We decided that the pantry needed a small light. We changed our 1 gang box to a 2 gang box that would house a switch for our dining room light AND the new pantry light. The dining room light has been wired the same for the 25 years we've lived here and have never had a problem with it. This is what we do know . . . the power source FIRST goes to the dining room light and THEN to the switch. This is a 12/2 wire. Upon investigation, there was a junction box in this line between the light and the switch, so we thought we could run 12/2 wire from the junction box to the new pantry switch then to the new pantry light. Well, we've got a problem and I need some help in navigating how to fix this. The switches work independent of each other. If I only use the dining room light, were good. If I only use the pantry light, we are also good. BUT, if I turn on the pantry light and then turn on the dining room light, the pantry light shuts off and the dining room light comes on. I have created a very amateur looking picture of my set up. Any help that anyone can offer would mean so much. I've wired alot of stuff, but this just seems impossible for me to understand. Thanks in advance!
Let's talk about wires, and their purposes, and let's mark wires according to color. (note that they are NOT so marked right now).
- Neutral (white) is the current return: it's "the way home" for current, which always travels in loops.
- Always-hot (black) is hot all the time. Of limited use for lights.
- Switched-hot 1 (red) is hot when you want light 1 on.
- Switched-hot 2 (blue) is hot when you want light 2 on.
Supply brings always-hot and neutral.
A lamp wants switched-hot and neutral.
A switch needs always-hot and switched-hot (but not neutral).
Here's the problem. Note the junction box to the switch. There was only ever 1 cable coming through there, and now you added a second parallel cable. This buys you nothing. The added cable won't have any wire functions in it that the original cable did not have.
How things were before
Before, the cable on the left brought always-hot and neutral from supply. So those were black and white, and they were accurately colored.
Then, there was a simple branch to a switch. There were only 2 wires, so they must be the wires they have to be: always-hot (black) and switched-hot 1 (red). They are not colored that, obviously, but it would behoove you to buy some colored tape and color them that.
As you can see, neutral is not present at either the junction box or the switch box. Running a redundant cable from junction box to switch buys you absolutely nothing: you are simply doubling wires you already have at the switch box: always-hot and switched-hot 1. Bringing them a second time is futile.
Getting what you need where you need it
What you need over at the new lamp is always-hot 2 (blue) and neutral (white). You have the right idea sourcing always-hot 2 from the switch, but this leaves off any way to bring neutral - and all related wires must travel in the same cable! You're not allowed to have loops, triangles etc. (the parallel wires between junction box and switch are kind of a loop, and as said, pointless; they should be removed.)
The /3 method
As you can see, the only place to source neutral (right now) is from the original lamp. If you can upgrade the run from that lamp via the junction box to the light switch, into /3 cable (black white red), then that will bring neutral to the light switch and all this will work out. That will also bring you into compliance with NEC 2011 rules about neutral at light switches, which is for just this sort of situation.
The smart-switch/module method
The other option I see is to rewire the original lamp so it operates with a smart-switch and partner control module sitting up in the lamp ceiling rose. At that point, we will re-task the wires from lamp via J.box to switch, to be Always-Hot (black) and Neutral (white). The smart switch will need this anyway for power.
At that point, always-hot and neutral are present at the switch, and again your plan works out.
You are trying to feed your new light from a switch loop and as you've found out, it doesn't work. You have your source, hot and neutral, going to the hanging lamp. There, the neutral is tied to the lamp.The 12/2 going to the junction box and to the switch box is the always hot, probably the white, and the switched hot, probably black. That's what you spliced into, there is no neutral and you need one. One solution is to run a 12/2 source, hot and neutral,from the lamp to the light, hook your neutral to the lamp and then run your switch loop to the switch box. Disconnect the wire you ran from the junction box to switch 2. When running a switch loop, the always hot is supposed to be the white wire and it should be marked with some black tape to differentiate it from a neutral wire.