Two pairs of Romex wires into box -- not a 3-way or switch loop -- help!

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Old 10-06-12, 08:36 PM
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Two pairs of Romex wires into box -- not a 3-way or switch loop -- help!

I am replacing an outside light fixture and the electrical box has two sets of romex wires. One of the wire pairs (the grounds are capped together) is controlled by a wall switch but the other wire pair seemingly does nothing. If it were a switch loop one black would be hot when the switch was off -- which it is not. I am pretty sure this isn't a 3-way either since there is only one switch.

When I took the original fixture off I believe (not sure about this) that both blacks went to the fixture (one hot and one neutral presumably) and the whites were tied together.

Any ideas or suggestions as to what is going one here and how I should mount my new fixture that requires one hot wire (standard fixture)?

Thanks.
 
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Old 10-06-12, 08:45 PM
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When I took the original fixture off I believe (not sure about this) that both blacks went to the fixture (one hot and one neutral presumably) and the whites were tied together.
A black is never a neutral so your statement doesn't make sense. What color wires on the switch? What other wires in the switch box?
 
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Old 10-07-12, 08:53 AM
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Ray, thank you for your response.

There are two sets of wires going into the box: two black, two white, and two grounds. I realize what I said above about the black being used as a neutral is nonsense but that is what I seem to remember. Unfortunately I was overconfident with this task and didn't take careful note of the original wiring to the original fixture. Note that I attached a lightbulb to one set of wires and I can switch it from the wall switch. I am stumped about the second set of wires. All I remember for sure is all the wires were connected in some way, that is, the second set of wires was not simply capped and unused in the original fixture.
 
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Old 10-07-12, 09:25 AM
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Please tell us the wiring at the switch. It sounds like the second cable feeds another fixture that is or was controlled by the same switch. Baring any new revaluations I would cap off the second unknown cable and connect the known cable only. You can if you want look for the mystery light powered by the second cable or just wait till you accidentally find it later. I would not leave the cable connected because there is a possibility the other end is not terminated in a code compliant and safe way.

There is an outside possibility the second cable goes to a switched or half switched receptacle not a light but it would be unlikely in my opinion.
 
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Old 10-07-12, 09:36 AM
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I just had a look at the switch wiring and both wires connected to it are black (the switch only has two screws).

There is another switch in the same box with associated wiring but it controls an unrelated light.
 
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Old 10-07-12, 09:47 AM
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Thanks again for your help Ray. With regard to that outside possibility..., I just remembered (viz you reminded me) that there are two outlets in my garage that are controlled by the same switch that controls the fixture light. I never liked this since to use the outlets my light has to be on, but I guess this was done so the switch could control lights plugged into the outlets for additional outside lighting (the outlets are near the garage opening on either side).

Now what?
 
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Old 10-07-12, 10:07 AM
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Now I am looking at the garage outlets. When I wire up a bulb to the white/black pair that the switch controls the bulb goes on with the switch in the on position but the garage outlets are off. Thus, the second wire pair is needed for the garage outlets to work.
 
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Old 10-07-12, 12:12 PM
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Thus, the second wire pair is needed for the garage outlets to work.
I would abandon that second cable at the light and connect the garage receptacles to a constant source of power.
 
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Old 10-07-12, 12:30 PM
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Thanks Ray, I totally agree. I am now reasonable sure that the original installation had the two blacks tied together with a pigtail going to the fixture and the same set up for the whites. In this configuration the switch controls the light and the outlets simultaneously. Thus, I don't think I can abandon the cable and still get power to the outlets. For better or worse I may just wire the new fixture in the old configuration (blacks joined with pigtail to fixture) since I don't know how to get the outlets on a constant source.
 
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Old 10-07-12, 02:00 PM
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I don't know how to get the outlets on a constant source.
There are many ways. You could replace the 2-conductor cable from the switch with a 3-conductor cable. Do you have access from above to do that? Another and best would be to run a new circuit from the breaker box.
 
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