What is red wire on old BX cable for?

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Old 07-15-08, 07:14 PM
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Question What is red wire on old BX cable for?

I am tryingto fix an old ceiling light. There are 2 BX cables coming into the box. One has 2 wires (1black and 1white) but the other has 3 wires. 1 black 1 white and 1 red. My plan was to make a diagram before I took it apart so I could put it back together again with out a lot of problems.
My plan failed because the wires were old and the colors on them were gone. I had to pull more cable down and cut it back to where it was good again. I understand he concept of black to black and white to white, but what the hell is the red wire for and where do I connect it? At first I grouped it with the white wires and it blew the breaker, so I grouped it with the black. Now I can't turn the light off once I get it on. 1 set of wires goes to a wall outlet (I think) and the other (I know) to the light switch.
I can't seem to find where the other end of this red wire is. The guy at the local hardware said to just put a wire nut on it (the red wire) and connect the others. One of my old electrical books said that sometimes when a red wire is present it's hot. Putting a wire nut in a hot wite and just leaving it sounds like a fire waiting to happen.
Any help would be greatly appreciated.
 
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Old 07-15-08, 07:30 PM
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Without knowing where the other end is will make this harder but not impossible.

It may be a switched hot wire for the light. The black most likely is a constant hot.

Can you test between the red and white while someone operates the switch?
 
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Old 07-15-08, 10:54 PM
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Any three-way switches? Does the room have two switches, one which doesn't do anything?
 
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Old 07-15-08, 11:47 PM
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Often this would indicate another switch in a 3 way arrangement. Old homes often used 3 or 4 way switches, one at every door to control a light. They can be confusing to a layman and often are wired in screwy ways. Check to see if there are any other switches or boxes that were closed off.

Where was the red wire connected before you started? Do you have any way of measuring the voltage? This possible could be a 220 shared neutral circuit. In which case there would be 220 between the black and red and 120 between the white and black and white and red. the 3 or 4 way is much more likely though.

If you absolutely cannot fine an answer and everything else is working, wirenutting the lead is not a problem. Add some tape to make sure the wirenut stays on over time.
 
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Old 07-16-08, 06:18 PM
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I turned the main power back on and flipped the breaker to that light. I found myself standing in a dark basement so it's obviously on that same line.
I was looking through some old home repair books I had in my work shop. A 3 way is a possibility, there are 2 places where an old doorway was removed from the room. One led outside, the other into the kitchen, but I couldn't find any boxes that had been closed off.
In my book, 1 diagram shows a box where the power comes through the light and back to the switch, instead of from the switch to the light. Which makes sense now that I looked at a picture because otherwise I'd only have one set of wires running into the light box. In this case though one of the white wires is recoded to black and runs from the light back to the switch. If that's the case would having the white wire from the power source hooked to the other white wires (at the light) cause the light to stay lite?? I can't turn the light off with the switch Since I'm not using any 3 way I think I'll just wire nut and tape that red wire off.

I don't know where the wires ran before I started tinkering. The color was worn completely off. In hindsight I should have seen if I could pull more cable out first, striped off the armor, THEN looked to see what color went where. Being the moron I am I didn't do that . Usually I either make a diagram or take a close up picture with my camera. The batteries in my camera were dead so..... Like I said I couldn't tell what color anything was either so making a diagram wouldn't have worked. WON'T MAKE THAT MISTAKE EVER AGAIN!!I foolishly thought black to black, white to white. They were twisted together with wire nuts and the electrical tape was fried right to it. Something in there got really hot , that's what worried me about taping off that red wire.
 
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Old 07-16-08, 07:43 PM
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If it got hot enough to do that it must have been a poor connection at the wirenut. Arcing causes heat. Also sometimes very old tape may look heated when it is just old and dried up.

Do you have a meter or indicator? A meter would be better.

You can carefully scope out each wire. Separate the 2 and 3 wires. Have the ends of all wires bare, separated and well away from the box. Make sure there are no kids or anyone else that is in the area and will touch the wires. Turn the circuit on. On the two wire cable in the box there is a black and a white. Measure between them and from each to the box. If you get voltage here, hopefully on the black lead, then this is the feed BUT also measure the other 3 wires from the other cable in the same way.

Report back what you find. Don't forget to turn the power back off and cap the wires.
 
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Old 07-17-08, 11:29 AM
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I took the switch box apart and found the red wire
I am attaching a diagram of the whole mess.
http://i118.photobucket.com/albums/o...ghtdiagram.jpg

I don't have a meter, but I do have a bulb tester that I can use to find what wires are hot.

Any idea why the switches are hooked up like this???
At least now I know where that red wire goes. Does that mean I should group it with the other hot wires? I did that but it kept blowing the breaker. How do I determine which way the juice is flowing now? Switch to light or light to switch.
 
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Old 07-17-08, 11:41 AM
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The drawing shed some light but adds more questions. You show the red wire (and cable) going to the box drawn at right. Is this the light fixture? How are the wires connected in that box? This looks like a classic 3 way hookup. If there is not now it apears there was at least one other switch for the garage and this light - both switches are 3 way (3 connections) that you show.

If NO other known switch exists for these lights then you need to access the wiring and put just single pole switches in there. But ito do that you need to determine where the wires go, open the other boxes ans do some rewiring.

Any further information woul dbe helpful. Yes you can use a light for testing.
 
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Old 07-17-08, 11:44 AM
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As I suggested in post #2 the red looks like a switched hot, and the black is a constant hot.

If you want the switch to operate the fixture attach the fixture black to the ceiling red. Attach al whites together. Connect the 2 blacks together and cap.

The 2 blacks on one end of the switch are basically connecting power in and continuing it to another part of the circuit. as power out.
 
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Old 07-17-08, 12:31 PM
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I think pcboss has it. Another possibility is that there used to be a fan at the ceiling box and the black powered the fan and red the light.
 
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Old 07-17-08, 01:22 PM
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yes now that I reread your post with drawing that makes sense.

BUT is the black wire from the ceiling fixture the feed? Are there other wires in the ceiling fixture besides the cable from the switch (blk, red, wht) Your drawing shows other wires.

What might be the case here is that the blacks and whites from the two cables are connected in the ceiling fixture. This brings a complete circuit to the switch box. There the black (hot) lead is switched and sends current back up to the light fixture box, where it is used with another wire there to the white neutral to run the light.

Then back in the switch box the black hot loops to another switch. The other end of that switch and a neutral (white form light fixture) go to the garage light.

This is what I mean.

(Resize photo to 600x400)
 

Last edited by HotxxxxxxxOKC; 07-20-08 at 06:42 PM.
  #12  
Old 07-17-08, 07:03 PM
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Thanks dsc, I think that's probably how it was wired before I tinkered.
I did check today and the red white and black set of wires were all cold. I had them all separated and I used the light tester, the power source coming into the fixture box is the black and white set. I'll hook it up your way tomorrow and see if it works, sounds right though.
 
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Old 07-18-08, 11:02 AM
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dsc: THANK YOU THANK YOU!!!!!!
The light switch works, light now goes on and off like it's supposed to. That diagram was a great help so again thanks.

I still have to chase down where those other 2 wires go to on the garage part of that circuit. There is the possibility there may have been a 3 way at the entrance to the house and for what ever reason it was closed off. Is that an ok thing should I find that to be the case????
 
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Old 07-18-08, 11:59 AM
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I think you are talking about the left switch in the drawing? The wire out the left of the box? Are you sating the left switch does nothing?
 
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Old 07-18-08, 02:28 PM
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Actually the switch on the left operates the light fixture and the switch on the right goes to the garage. Don't ask me why it's set up that way I didn't wire it. I think this house was wired before indoor plumbing.
The switch to the garage has 2 sets of wires coming into the box. (see diagram again) 1 obviously goes to the light in the garage. I don't know where the other black and white wire hooked to that (garage) switch goes.
 
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Old 07-18-08, 04:35 PM
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OK so the right switch controls the garage light then?
and there is another cable - black and white that goes out of this box besides the one controlled by the switch?
 
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Old 07-18-08, 07:16 PM
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The switch for the garage has 2 black and 2 white wires coming into the box. 1 goes to the garage lights. I can't find where the other goes, or am I looking at this incorrectly? If the other (light fixture) switch powers the garage switch then the wires at the top of garage switch box are going "out", or is that wrong????
Maybe I should just up my fire insurance and be happy you got the light back working right for me and not worry where those wires go. Am I making a mountain out of a mole hill? Where ever they go they've been going there for a real long time. I've tried every switch in the house and I can't find one that works with it or isn't doing anything at all. The only other light on that circuit is a light in the pantry and it has a pull chain.
 
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Old 07-18-08, 08:34 PM
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My drawing showed just one cable out the left side. I did not label it but in my mind it was the garage. I have it as the left switch but position does not matter.

Is this what you have or is there yet another cable out the left to wherever?

If you have another cable and you cannot determine what it is you can disconnect it and cap it. That might make you feel better. Just remember later if you find an outlet or light tha does not work, that you did that!
 
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Old 07-19-08, 11:00 AM
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As near as I can tell the power comes into the fixture box first. Then it goes into the switch on the left which operates the light with the red wire. The black wire loops around the bottom pole and does a hop over to the bottom pole of the garage switch (right side switch). On the garage switch there are 2 sets of wires. Whites are all tied together. 1 of the black wires goes to the top pole and the other black wire goes to the bottom pole where it joins the wire that hopped over from the light fixture switch.

I have another question while we're at it. The breaker to that whole circuit is a 20 amp. The switches say 15 amp on them. Does it make a difference if the breaker is of a higher amperage?
 
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Old 07-19-08, 09:12 PM
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Originally Posted by Home wrecker View Post
As near as I can tell the power comes into the fixture box first. Then it goes into the switch on the left which operates the light with the red wire. The black wire loops around the bottom pole and does a hop over to the bottom pole of the garage switch (right side switch). On the garage switch there are 2 sets of wires. Whites are all tied together. 1 of the black wires goes to the top pole and the other black wire goes to the bottom pole where it joins the wire that hopped over from the light fixture switch.

OK. Well this (garage) switch does control a light right? If so, then take the other black wire going towards the garage or wherever, that you cannot identify, off of the bottom pole and cap it. then go around to every possible outlet, or wired light and make sure they work. If you cannot find anything that does not work then leave it capped - but remember you did that just in case six months from now you find something that does not work.

I have another question while we're at it. The breaker to that whole circuit is a 20 amp. The switches say 15 amp on them. Does it make a difference if the breaker is of a higher amperage?

No that is OK but is the wire #12??? If it is #14 it should have a 15A breaker. Old wire like this is often #14. You can compare it to a piece of known size or use a wire gage. Also a wire stripper will work in a pinch. It should fit just over but not nick the proper size bare wire.
 
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Old 07-20-08, 07:25 AM
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Thanks I'll check the wire size today.
What happens when a breaker has a higher amperage than necessary? Will it cause a possible fire in the walls or box?
 
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Old 07-20-08, 08:10 AM
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If the breaker is oversized in regards to the wire too much current could flow causing the wire to heat up too much before the breaker would trip. This could lead to a fire.
 
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Old 07-20-08, 04:23 PM
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I'm really glad I asked what felt like a dumb question. I checked and you were right it is # 14 wire. I'll pick up a new 15 amp breaker tomorrow, have to go to Lowes to look for a new door anyway.
 
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Old 07-20-08, 06:17 PM
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There is no such thing as a dumb question! Glad you got things back together there.

As you have time you should probably check other circuits. Most old house wiring was #14, so most breakers will be 15A. It is often good to rewire the kitchen and bath, basement, outside to bring them up to code with GFCI's and 12 gauge 20A circuits qwew required.
 
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Old 07-20-08, 07:24 PM
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Will do and thanks again for all of your help. You've been most helpful!!
My Grandpa used to say the only dumb question was the one you didn't ask, but then he'd slap me up side the head when I bugged him with my "dumb" questions.
 
 

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