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I'm trying to replace an existing single pole switch with a dimmer switch for a 4 bulb vanity light. Trying to replace with a Lutron DVCL-153PR-WH switch. Upon opening the box I am faced with 2 red wires and a yellow wire. No ground and the beige wire is capped off in the box. New switch has a red, black, red/white striped, and green ground wire coming off it. Existing switch appears to be single pole as it doesn't control anything else except vanity light. The presence of the 2 red and a yellow is throwing me off. Looking for some help. I have included photos:

Wiring inside switch box

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    Beige is almost certainly aged white (and neutral, for sure, in conduit, barring code violations.)
    – Ecnerwal
    Oct 7, 2022 at 1:13
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    Good to see you replaced that switch because it was not wired very well. The wire should have been looped around the screw. Looks like the switch may have a clamp style screw on there which is why there's no loop. I point this out as you may have other switches/outlets that are a potential fire hazard. Oct 7, 2022 at 2:49
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    To reinforce what @PlatinumGoose said, please see this pic. As that wire was tightened down, the screw was forcing it out of the clamping area (see red arrow). The wire should have been inserted into the slot in the blue plastic (green rectangle) in the direction of the green arrow, and gone under the brass plate. Then when the screw tightened, the wire is clamped under the brass plate. (This would apply to all the wires on this switch. There's even a big yellow sticker that says how to do it...
    – FreeMan
    Oct 7, 2022 at 15:18
  • Fortunately several other switches have been replaced with home improvements over time but this is something I will keep in the back of my mind. Installing this dimmer switch really exposed me to some electrical knowledge. Thanks!
    – Bueller
    Oct 7, 2022 at 19:05
  • While I'm at it... I just noticed that in the next to last pic, there is some copper showing in the neutral wire bundle. That's a no-no. Either that one wire wasn't pushed up far enough into the nut (and electrical contact it minimal at best) or it was stripped too far and needs to be trimmed to match the length of the other wires.
    – FreeMan
    Oct 7, 2022 at 22:04

1 Answer 1

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Whites are neutral. If your new switch needs neutral, add a short white wire (pigtail) and connect it to the others.

Metal conduit + metal boxes = strange wire colors and grounded automatically. All switches, better quality receptacles ground automatically with metal boxes.

In the old switch, one red is incoming hot, one is outgoing hot, yellow is switched hot.

  • Connect the two reds to black of the new switch with a wire nut.
  • Connect yellow to red of the new switch.
  • Cap the striped red.
  • Connect the green ground wire from the new switch to a grounding screw in the metal box. If the green wire is removable (not clear with a quick look at the instructions) then you can remove it as the switch will ground to the metal box through the yoke.
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    Perfect! just wired the dimmer switch and it works exactly as desired. Thanks for the help and explanation. It made a ton of sense!
    – Bueller
    Oct 7, 2022 at 0:06
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    @Bueller, note that in this case red is incoming/outgoing hot and yellow is switched hot. The colors could be different in other boxes in your house, though one would hope the electrician was consistent. There is no requirement that he be consistent (other than the general "workman like manner" for doing work). If he ran out of yellow, he may have used any other color (except white, grey & green) as a switched hot...
    – FreeMan
    Oct 7, 2022 at 15:20
  • @FreeMan thanks for calling that out. I've already thought the same thing. I just recently replaced 2 light fixtures in the hallways and they were wired with he appropriate color wires. My initial thought was the electrician ran out of a color and just kept going. House is 40 years old, so who knows going back that far.
    – Bueller
    Oct 7, 2022 at 19:03

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