Why a Red Wire in Box? Newbie

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  #1  
Old 10-11-04, 04:01 PM
capitolhill
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Why a Red Wire in Box? Newbie

I'm replacing a light fixture in a bathroom. (It's an old house, but I'm not sure how old the wiring is.) There are white, black and red wires coming into the box. There is a wall switch that contols the power to the light.

The fixture I'm replacing used the white and RED wires. This confused me -- I thought that the white and black wires were ALWAYS used. The fixture was acting up -- maybe this was the problem. There is no ground wire connected to the box itself.

Can I safely assume that the red wire is ground? Why red? Is this a standard color? How could I confirm this safely? I have a digital voltmeter and know how to use it.

Thanks.
 
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Old 10-11-04, 04:11 PM
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Is there a second wall switch that controls that same light? In that case the red is a "traveller" wire.

Explain the layout of the box in more detail.

The red may be a hot wire.
 
  #3  
Old 10-11-04, 04:31 PM
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NO NO NO the red wire is not a ground. Connect the new fixture the same as the old one. Use the red and the white. Connect the red to the fixture black.

Is there a receptacle beside the switch. The black wire is carrying power to the receptacle. The white wire is the neutral for the receptacle. The red wire is the switched power coming back from the switch.
It could also be an unused wire ready to be connected to a fan.
 
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Old 10-11-04, 05:08 PM
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Treating the red wire as a ground would be a quite effective suicide attempt!!

I'm guessing that the old fixture had an integrated receptacle, and the new fixture does not. True?

Joe's instructions are correct. Connect the red to the fixture black. Be sure to put a wire nut securely on that black wire in the box. It's hot (even with the wall switch off) and you don't want it to touch anything or there will be fireworks.
 
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Old 10-11-04, 05:52 PM
capitolhill
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Red Wire

Thanks guys, for the quick and helpful responses.

You asked if there was an "integrated receptacle" in old fixture: do you mean a non-switched electrical outlet? Yes, there was one. I suppose that then you were saying that the box has white (ground), black (always hot, for outlet) and red (switched hot, from wall switch). This makes sense to me now.

What throws me is that in my limited electrical experience I've not see the red wire or a mention of it in 'home handyman' type books. Is red a standard color for the wire that comes off of a switch?

Also, the lamp has a bare braided ground wired and a metal bracket with a screw that the ground wire is supposed to be attached to. I'm assuming that I do not need to run another wire from the bracket to the box, since ground would be completed once the bracket is screwed into the box, right? Do some homes have a dedicated ground wire in the box? If not, can I assume that the box itself is grounded?

Thanks again.
David




Originally Posted by John Nelson
Treating the red wire as a ground would be a quite effective suicide attempt!!

I'm guessing that the old fixture had an integrated receptacle, and the new fixture does not. True?

Joe's instructions are correct. Connect the red to the fixture black. Be sure to put a wire nut securely on that black wire in the box. It's hot (even with the wall switch off) and you don't want it to touch anything or there will be fireworks.
 
  #6  
Old 10-11-04, 06:48 PM
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Is red a standard color for the wire that comes off of a switch?
I'm not quite sure I'd call it "standard", but it's very, very common.

Do some homes have a dedicated ground wire in the box?
Most homes outside of Chicago built in the last 30+ years do.

If not, can I assume that the box itself is grounded?
You cannot assume it, but you can test for it.
 
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Old 10-11-04, 06:52 PM
capitolhill
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Job finished - final question

Thanks again for the assistance.

One last question: what's the best way to test that the box is grounded, since there's no ground wire? Do I use a analog meter and check for 0 ohms between the box and a pipe or outlet ground pin?

David
 
  #8  
Old 10-11-04, 06:54 PM
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First a correction on your terminology. The white wire is not a ground. It is a neutral, or return wire. It carried the current back to the panel after it powers the light to complete the circuit. It is grounded, which may be what is confusing you, but it is not a ground wire.

A ground wire would be a separate bare or green insulated wire. Ground wires were not used years ago, so your bathroom may not have them. Connect the ground wire from the light fixture to the metal box.

As for red wires, they are quite common, and I am surprised that you have not heard of them. Red is typically the first color used when a normal NM type cable has more than two wires. A red wire is a hot wire. It can be always hot or switched hot, but it is a hot wire. It should never be used as a ground wire or as a return wire. Most of the time it will be used as a switched hot wire in a cable that has an always hot wire and a neutral/return.
 
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Old 10-11-04, 11:05 PM
phillyguy
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To test if the box is grounded simply touch one end of a multimeter to a hot wire and the other to the box itself. If you get 120v then the box is grounded.
 
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