I'm trying to replace a dimmer switch in my house and what I expected would be a really easy job is looking more complicated than I expected.

The current switch is a simple rotary dimmer. It has two black leads and a green. The green isn't attached to anything (the house is 100+ years old, though the wiring is redone).

The wall box has a white and a red wire coming in on one side and a white, red, and purple wire coming in on the other side. The two white wires are spliced together. The two red wires are also spliced together, but also have one of the black wires from the switch spliced in. The other black wire from the switch is spliced to the purple lead.

The new dimmer switch has red, white, green and black leads. I expect the white would splice in with the two white wires, but what about the red and the black?

From reading the forum I'm wondering if this might be wired as a three way switch, but there's nothing else that controls the light.

I've attached a couple of photos. They aren't great, it's rather dark where the switch is located. Hopefully they're good enough to make out what's going on.

Any help would be great. Thank you!

 

Is it a motion sensor or dimmer. I never heard of the two being combine. Black should be power in, the wire in your box that is always hot. Red should be power out to the light. White is the neutral and goes to your other neutrals as you wrote.

 

I think I'd start by reviewing the schematic that should have come packed with the new dimmer. As far as your house wiring at the box, I think that the two reds are power in and power out to the next box. Each would have a white neutral associated with it. The purple is probably the switch leg. So.........I am just guessing that the black wire on the dimmer goes to the two reds in the wall box and the red on the dimmer goes to the purple in the wall box. The white on the dimmer would connect to the two whites in the wall box. The green on the dimmer would attach to the metal box as I believe this wiring is in conduit and there are no ground wires entering or leaving the box. You really need a meter to determine if my assumptions are correct before proceeding and above all else, be sure the circuit breaker is OFF before trying to wire a dimmer. This is only a guess on my part, you really need to check the schematic.

 

Thanks you for your replies.

The new switch is indeed a motion sensing dimmer. It acts as a motion sensor that dims the light to and from full brightness and also has a dimming control setting. Here's the exact product: Cooper Wiring Devices OS106D1-GY 600W PIR Occupancy Sensor Dimmer Switch - Gray - Smarthome

The schematic is as follows, and sounds like it matches with CasualJoe's assessment:

Hot Black -> Hot Black on switch
Ground bare -> Green on switch
Neutral White -> Neutral White on switch
Output Red on switch -> Black on Fixture

 

Welcome to the forums!

From your description of the wires, the appearance of the box in your photos and your location in Illinois, it appears that you have wiring run in grounded conduit. Given that, use a rated ground screw to terminate the green wire on your control to the grounded metal box. Because your new switch incorporates a motion sensor, it needs power. To provide it a complete circuit, ad the white wire on it to the splice with two white wires in it now, as you said.

That leavesThe red-wire splice is ungrounded power entering and leaving. Add the black wire on the switch to that splice. Splice the red wire on the switch to the single purple wire.

 

Thank you all very much for your help!

 

You're welcome. Did you get it to work?

 

Yes, it worked great. All your help was very much appreciated.

 

Great. Thank you for the feedback.