Color of wiring

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  #1  
Old 09-22-05, 09:25 AM
ronaldneil
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Color of wiring

I am trying to put a new fixture in , I find white wire, black wire and a red. What is the red wire used for? I am used to the white , black and ground. Thanks
 
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  #2  
Old 09-22-05, 09:42 AM
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It would help if you provided more information. What type of fixture are you trying to add? Are you replacing something, or trying to add new wires to add a new fixture somewhere else?

If you are replacing something, just wire it the same as what you are replacing. If this is new then you need to full understand the wiring in place.

Generally speaking, cables that contain a red wire are used for two main purposes in residences. They are used for three way and four way switches (where a single load can be controlled by more than one switch) and they are used where it is desired or necessary for there to be switched and unswitched power or two separate switched power runs. When used for switched and unswitched power it is generally the red wire that is switched.

Provide some more details and we can probably figure it out.
 
  #3  
Old 09-22-05, 09:47 AM
ronaldneil
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I hired a handy man to take down a hunter fan (no light attached)and replace with a hanging Light fixture. He took down the fan but never retured
to complete. There are 2 blacks 2 whites an one red.I do not know how the were originally attached. Thanks For your reply
 
  #4  
Old 09-22-05, 09:56 AM
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Most likely the red wire is switched by the wall switch and the black wires are always hot. Power may come in on one set of black and white wires, or power may go on to another item on the circuit.

Use a tester to confirm this before you begin, but you will probably find switched power between the red and white wire and unswitched power between the black and white wire.
 
  #5  
Old 09-22-05, 11:12 AM
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I believe that racraft is wrong in his description of what the wires do, but the fact of the matter is that both he and I would be guessing without further information. Testing is called for.

You will need to examine the wires going to the switch, and you will need to use an electrical tester on the bare exposed wires _with the circuit on_. If you are not comfortable with this sort of testing, then call an electrician now.

As racraft said, the red wire is _often_ used where you want a single circuit to carry both switched and unswitch power. But in general, a red wire may be used anywhere a black wire is used, and for any purpose that a black wire may be used, and the only reason for the red is to make it easy to separate whatever two functions you've assigned to the red and the black.

A _very_ common use for a red wire in a ceiling fixture is to permit two separate switches to control two separate loads, for example, the red wire might control the fan, and the black wire might control the light. It is quite common for this sort of cable to be installed simply to allow the possibility of having a separate control for the fan and the light; if a single load only is installed, then one of the wires will simply be capped off and unused.

My _guess_ is that you have a switch loop on 3 conductor cable. Power is supplied to the ceiling junction box on one cable, and then fed to the switch using another cable. This other cable provides for two separate switches, but only one is used. Again, this is just my guess.

The first thing that you need to do is make sure that the power is off to this circuit. You do this with an electrical tester, testing between every pair of exposed wires, and between every wire and ground. Nothing should turn on the electrical tester.

Next make a complete map of the wires in the ceiling junction box. Describe the color of the wires, and where the wires feed from. Usually wires are fed in cables or conduit, and so will be in defined groups. For example, you might have two separate cables, one with a white and a black, the other with white, black, and red. Look to see if there are bare ground wires pressed into the box, of if the wires are fed in armored cable (looks like metal hose), or if the wires are fed in conduit.

Next take the switch out of the wall, and look in the switch box. Do not disconnect any wires from the switch, but just look. Describe every wire that you see, how it is connected to the switch, if it bypasses the switch, or if it is 'capped off'. If wires are running in cable or conduit, describe which wire goes to which cable or conduit.

Now replace the switch safely back into the wall. Make sure that all of the wires in the ceiling box are separated. Turn the power on, and carefully test each pair of wires and each wire to ground. Note which pairs of wire provide power. Again record wire color, and what conduits or cables the wires are associated with.

With this information, we will be able to tell you how to connect the wires.

-Jon
 
  #6  
Old 09-22-05, 11:29 AM
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Jon,

I did consider the possibility of a switch loop, but did not mention it to keep from muddying the water.

Obviously the best and most appropriate solution is to examine the wiring at the switch to know how to proceed.

Other clues could be gained from the existing connections in the ceiling box.
We know that a fan was removed that had no light. Most likely the guilty party who removed the fan did not mess with any wiring not connected to the fan's wires. We could gain much if we knew what the other connections are in the box. Unfortunately we were not provided that information, and in fact rarely are.

I was attempting to keep it simple. Perhaps I over simplified it. I hope not.
 
  #7  
Old 09-22-05, 11:51 AM
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IMHO entirely reasonable to keep things simple.

I was focused more on a detailed 'this is how you get the additional data'.

Perhaps we both should have said 'there are lots of possibilities for that red wire, we need to know more to figure out what it is'.

*grin*

-Jon
 
  #8  
Old 09-22-05, 01:51 PM
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99% of the time, you'll be right if you:
  • Connect both black wires in the ceiling to each other, but not to your fixture.
  • Connect both white wires in the ceiling to each other, and to the white wire from your fixture.
  • Connect the red wire in the ceiling to the black wire from your fixture.
  • Connect all green and bare grounding wires in the box.
 
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