Replacing old dimmer ran into incomprehensible tangle of wires

Question

There are two old dimmer switches in this box, I wanted to remove one and replace it with a normal switch and now I am facing this -- I accidentally removed two of the three wires of the dimmer I want to keep.

There are four holes in the box.

The one on the bottom has two red wires and a white (the white is a bit off color but it's old enough that I think it's still white).

Then a white and a black leaves on the left.

A white and a black leaves on the top.

Another hole features a yellow-with-black-stripe (that's a protective ground, isn't it) and a white.

Finally we have a naked copper wire connected to a screw in the box. That's also some sort of ground, I would guess.

The whites from all four holes are connected together, I don't think I touched this because it still has the cap on and I doubt I need to.

Dimmer #2 has a bottom red wire connected to one of its black wires. It has another black wire and a green wire. I need to connect these but I can't figure out where.

Switch-to-be-installed has three wire nuts, one for ground and two for switching.

I don't get it. My guess would be that the two lights are powered by a black and a white wire exiting to the left and to the top. But that's not possible because the black wires are fixed to the red wire from the bottom which is ought to be phase 1 based on its color and then they would be powered always. I just don't understand what I am looking at. Dimmer #2 actually switches an outlet and currently there's no power in it.

Answer 1

I'd say those unusual-colored wires are actually reclassified hot wires, and are most likely the load for your switches. Since you said one switch controls outlets, that leaves the 4th bundle of wires as the connectors for your non-switched outlets. Since you're not installing smart switches, motion switches, or lighted switches, you can leave the neutrals as they are.

Your home uses metallic conduit and terminates in metal boxes, so you won't have ground wires. Instead there'll just be a single bare wire connected to the junction box. Both switches will connect to this using a wirenut.

I would assume the bundle of 3 cables at the bottom is for your switched outlet, and since red is currently connected to line, that leaves the orange-black wire as your outlet load, which you still have hooked up to a dimmer (which isn't allowed). On your replacement non-dimming switch, connect the orange-black cable to one black lead, and connect the other black lead to the bundle with the red wire (this is your power source).

That leaves the dimmer. The lights are most likely the yellow-black wire, which is your light load. If your dimmer switch specifies a terminal for load, then the yellow wire connects there. The other black lead is power in, which will pigtail with the red bundle just like the other switch.

Make sure this connection is very secure, since this is line voltage to everything in that room. Double check the wirenut you use too, since some of the wires look frayed from being disconnected. You don't want this bundle touching the metal of the junction box.

Finally, all greens (your ground connections) will pigtail with the bare copper wire. Technically this isn't necessary depending on the design of the switches, since the box itself is grounded, but if they provide a ground wire then better safe than sorry—especially on dimmers, which might have a separate internal ground. Plus, your box looks rather recessed, so I wouldn't trust the effort it would take to ensure a proper connection against the rim unless you know the screws aren't also isolated.

Answer 2

Your house is wired in the EMT metallic conduit wiring system. The EMT shell carries ground everywhere. Switches ground off their mounting screws. (receptacles do if they are marked "self-grounding"). All your conduits have [1-2] colored wires + 1 white wire.

That means all white wires are in fact neutral.

All the colored wires are hots. Yellow w/black stripe is a valid HOT color. In conduit, all wires' native insulation states which they are of

• neutral (white or gray) and
• ground (bare, green, yellow w/GREEN stripe).
• any hot (any other color)

The colors do not indicate what kind of hots they are (switched hot vs travelers).

I see 3 hot wires from 3 pipes grouped together. I gather these will be always-hot from supply and onward to 2 outlets or other points of use.

That leaves 2 hots unaccounted for. I see space for two switches. Those must be switched-hot for 2 loads.

The yellow-black makes perfect sense as a switched-hot color. So does orange (that is not two reds, it is red-orange).