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Old 09-16-2012, 08:02 PM   #1
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Wiring a new light fixture, not what I expected


Good evening all,

We're wiring a new dining room light fixture. We did not have the luxury of seeing the previous fixture installed when we moved in so we're not sure how it was wired.

Here's the setup: In the box on the ceiling we have a three wire (W, B, G) and a four wire (W, B, R, G) cable in the box. The blacks are capped together. The whites are capped together. The grounds are screwed together and the red is capped alone. There is a rotary dimmer on the wall. Looks like 3-way wiring in the box and I suspect there is another switch in an adjacent room but have yet to find it. There are several switches that seem not to power anything at all. We just moved in recently so there's still much to be done.

The Black on the three wire is hot.

Config 1: At first I thought it was supposed to be W-W-W, B-B-B, G-G-G and R capped by itself. In that configuration the light is on and cannot be turned off or dimmed at the dimmer.

Config 2: B on fixture to R on 4-wire. Ws capped. Bs capped. Light is not on, and dimmer does nothing.

Config 3: On another forum someone suggested that the correct configuration was B on the 3-wire to W on the 4-wire. Remaining B, W ,G/G in box connected to B, W, G on the fixture. Red capped. Can't do that. Hot B on 3-wire shorts when connected to W on 4-wire.

What do I need to determine in order to move forward and wire this properly? Any insight at all would be appreciated.
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Old 09-16-2012, 08:14 PM   #2
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Wiring a new light fixture, not what I expected


Connect the fixture to the white bunch and the red wire.

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Old 09-16-2012, 08:31 PM   #3
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Wiring a new light fixture, not what I expected


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Connect the fixture to the white bunch and the red wire.
Hi Joe, I did that in Config 2 mentioned above. Black on fixture was connected to Red on 4-wire. 2 blacks in the box were capped as well as the remaining 3 whites.

The light was not on and the dimmer did not control it. I was certain this configuration would work. Is it possible that whatever other switch is on the circuit (broken, miswired) is preventing this configuration from working as it should? I'm not even sure how I'd test it since there are at least a half dozen other switches in the adjacent rooms that do not apparently control anything at the moment. Any one of them could be on the circuit.

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Old 09-16-2012, 09:10 PM   #4
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Wiring a new light fixture, not what I expected


Could be a bad dimmer.
What wires are connected at the dimmer?
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Old 09-16-2012, 09:27 PM   #5
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Wiring a new light fixture, not what I expected


Hi jbfan,

The dimmer has just two black wires on it.

Two cables into the switch box. One 4-wire and one 3-wire. Grounds from both are screwed to the box housing. Whites from both cables are capped together. Black from 3-wire is connected to black from the 4-wire as well as one of the blacks on the dimmer. Other black from the dimmer is connected to the Red on the 4-wire.

Strangely, none of the wires on either cable appear to be hot. Breakers downstairs are fine.

So I assume the 4-wire in the switch box is the same 4-wire in the ceiling box. 3-wire in the ceiling box (the one with the hot black) must be from another source, no?

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Old 09-16-2012, 09:39 PM   #6
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Wiring a new light fixture, not what I expected


You do not have a 3 way set up.
With the breaker off, bypass the dimmer then turn the breaker back on.
Everything sounds like it is wired correctley
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Old 09-16-2012, 11:17 PM   #7
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Wiring a new light fixture, not what I expected


Replace the dimmer with a regular switch and test. I suspect a bad dimmer.

Configuration 2 should be correct.
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Old 09-16-2012, 11:43 PM   #8
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Wiring a new light fixture, not what I expected


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You do not have a 3 way set up.
With the breaker off, bypass the dimmer then turn the breaker back on.
Everything sounds like it is wired correctley
Quote:
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Replace the dimmer with a regular switch and test. I suspect a bad dimmer.

Configuration 2 should be correct.
Thank you both. I'll try the bypass/switch replacement in the morning.
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Old 09-17-2012, 08:41 AM   #9
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Wiring a new light fixture, not what I expected


The red wire in the dimmer is the switched power to the light. The dimmer is bad if connecting to the red and whites did not work.
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Old 09-17-2012, 08:52 AM   #10
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Wiring a new light fixture, not what I expected


You were absolutely right. Bad dimmer. First, I bypassed it this morning and the fixture lit. Then I installed a new dimmer and voila, it worked fine with config 2 as it should. Thank you both for pointing me in the right direction! I appreciated it. Seems obvious now, but when I was working on it yesterday I made the incorrect assumption that the dimmer was functional.
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Old 09-17-2012, 08:52 AM   #11
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Wiring a new light fixture, not what I expected


Quote:
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Hi jbfan,

The dimmer has just two black wires on it.
All the dimmer switch does is interrupt the hot wire. One hot to one wire on the switch, the other wire is the hot out or in...doesn't usually matter. Shut off breaker when doing any connections.





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Old 09-17-2012, 10:47 AM   #12
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Wiring a new light fixture, not what I expected


Quote:
The dimmer has just two black wires on it.
josephmartins, just for clarification, the dimmer itself has two black wires coming out of it, but one of those wires is connected to a black wire and the other a red wire, correct?
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Old 09-17-2012, 11:09 AM   #13
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Wiring a new light fixture, not what I expected


Black power in, red power out.
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Old 09-17-2012, 12:24 PM   #14
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Wiring a new light fixture, not what I expected


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josephmartins, just for clarification, the dimmer itself has two black wires coming out of it, but one of those wires is connected to a black wire and the other a red wire, correct?
Yes, one of the Bs from the dimmer was connected to the R on the 12/3 cable that runs from the switch box up to the ceiling box. The other B was capped together with a B on the 12/3 and another B on a 12/2 cable that I assume continues power over to some other fixture.

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