Confused by Dimmer Wiring

Question

I have a light on a dimmer that flickers so I was going to remove the dimmer and put a regular single pole switch. I've changed switches before so I'm familiar with changing switches when the power goes to the switch or the power goes to the light. I was a bit confused by what's going on when I turned off the power, opened the switch and saw the following (image included):

Two 14/2 cables coming into switch box:

1. Two blacks from both cables are twisted together with yellow nut
2. Two grounds from both cables are twisted together. The first red from the dimmer is taped to the grounds (behind the orange nut on the left)
3. The second red coming from dimmer is unused and still has the sticker saying not to remove.
4. White from one cable is twisted to black from dimmer (orange nut on right)
5. White from other cable is twisted to green from dimmer (orange nut on left)

One 14/2 cable coming into the light fixture:

1. Black wire from cable attached to black wire on light fixture
2. White wire from cable attached to white wire on light fixture

Thanks for any help figuring this out!

Answer 1

Oh dear, some dim bulb wired this dimmer upside down and backwards

Whoever installed this dimmer clearly hasn't a clue, because they wired it in a way that's been forbidden for the past almost-a-century now! In particular, they put the dimmer in the neutral side of the circuit, instead of the hot side, where it belongs. The NEC prohibits this in section 404.2(B):

(B) Grounded Conductors. Switches or circuit breakers shall not disconnect the grounded conductor of a circuit.

Exception: A switch or circuit breaker shall be permitted to disconnect a grounded circuit conductor where all circuit conductors are disconnected simultaneously, or where the device is arranged so that the grounded conductor cannot be disconnected until all the ungrounded conductors of the circuit have been disconnected.

Furthermore, they managed to abuse the safety ground as a neutral (a working current return path) and the neutral as a half-hearted grounding attempt, giving this setup even more zap potential than it normally would have!

Getting this fixed

The first step in fixing this is to turn the breaker off, remove the errant dimmer from the circuit, and use a multimeter to check for continuity between the white wire that the dimmer's green wire was connected to and the bare wires in the circuit. If you don't have continuity there, the feed for this box will need to be reworked due to the neutral having gone bad.

If you do have both a good neutral and a good ground going back to the panel, though, we can move on with fixing this then. To get this into a proper state, we need to undo the dodgy tape-splice on the grounds and replace it with a proper wirenut, incorporating the green ground wire from the dimmer into this redone splice, then remove the wirenut from the two black hots and use a new wirenut to splice the white neutrals together. Once that's done, one of the black wires from the wall gets nutted to the black wire on the dimmer, and the other black wire on the wall gets nutted to the un-taped red wire on the dimmer. At that point, you can button things up, turn the power back on at the breaker, and enjoy your dimmer without having to worry about any shocking moments, during lightbulb changing or otherwise!