Replace Electrical Light Switch
April 28, 2024 6:18 PM   Subscribe

I am replacing an old (though functional) dimming light switch. Photos here

You see that I have the new switch with green, red, and black wires connected. Note that there are a total of 4 wires for the black, 3 each for red and green. In this wiring configuration, the light is always on. The switch has no effect. I also tried switch places with red and green wires. Same problem.

What am I doing wrong?
posted by falsedmitri to Home & Garden (9 answers total)
I should be able to help but some more info would be very useful.

1. What country are you in?
2. How were the wires connected to the old switch?
3. Can you share a photo of the instructions for the new switch where the wires are labeled?
posted by dbx at 6:56 PM on April 28

Best answer: The wiring diagram for your switch is here.

Whichever two wires in the junction box that were connected to the old switch should be connected to the black and red (untaped) wires of the new switch. The green wire should be connected to the shared ground.

Your photos are blurry where it counts unfortunately. Is that a loose black wire on the right not connected to anything? Is your red wire connected to the whites? What is your green wire connected to?
posted by dbx at 7:09 PM on April 28 [1 favorite]

Best answer: Anyway, here's my best guess on the correct configuration for you. I won't see any replies until morning (eastern US) at this point.

The two black wires that are twisted together are probably hot. Those probably connect to the black wire on the new switch. The lone black wire on the right probably goes to the fixture and should connect to the untaped red wire. All white wires in the box should probably be connected to each other and not connected to the switch. The green wire should connect either to thebox or to a bundle of green or bare wires if one is present.

All of the above is based on standard practice in the US and may vary significantly depending on your location.
posted by dbx at 7:15 PM on April 28 [2 favorites]

Response by poster: Sorry should be said... U.S..110v
I'll get to this tomorrow. Too tired to be conscientious about this now
posted by falsedmitri at 7:31 PM on April 28 [2 favorites]

Never do anything with electricity without being conscientious about it!
(And kill the breaker)
posted by Windopaene at 8:31 PM on April 28 [3 favorites]

Best answer: Getting shocked is Not Fun. If you have a friend who knows what they are about, give them fifty bucks, make good coffee, be prepared to run to supply store for this or that.

I've spent a lot of my life in the trades, I have done some electrical fixes (changing out breakers, both main and breakers in the box}, I'm generally not afraid of tackling this and/or that. But I've been blasted a few times when fucking around with electrical jive and I tend to ask my friend Jimmy for help -- he is plumbing and electrical god.

I just don't like to get blasted, even at lower voltage stuff. I'll do it , I've done it, I'll do it again, but if Jimmy is around I'll smile at him et cet. I'm better at all kinds of carpentryll, and anything he needs from me he gets.
posted by dancestoblue at 12:51 AM on April 29 [1 favorite]

Best answer: House wiring has gone through at least three major phases. If the house is a few decades old, it may be in an earlier phase that is different from what is assumed by such instructions as may have come with the new switch, or what you are likely to find on YouTube DIY videos.

I ran into this while installing a ground fault interupter in my 1960 era house. The telltale was the house wiring was encased in a metal shielding which is the ground and attached to a metal junction box.

Home Depot has some info.
posted by SemiSalt at 5:15 AM on April 29

IMO, you need to get a tester - a multimeter. They are $10 on amazon, or probably the same at HomeDepot or Harbor Freight. It will make things like this much easier. Watch a youtube video on how to use them. You will use it more than once.

Black one goes to the line that is live when you test it with the power on.

Red one goes to the fixture.

Green is ground. It doesn't look like you have 3 wire, with a ground (not a 3 way switch, that's what the taped line is for on the switch), coming into that outlet. That stinks.
posted by The_Vegetables at 2:53 PM on April 29 [1 favorite]

The_Vegetables, it's possible that the house has metal conduit, in which case the junction box itself is grounded. The green wire would need to be bonded to the box in that case. The newish type of wires, combined with no visible sheathing, tells me that is a real possibility.

You are correct that the way to check for that would be a multimeter. falsedmitri, if you go that route I'll walk you through it.
posted by dbx at 4:29 PM on April 29 [1 favorite]

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