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Any way to send a small current down a wire to identify it?

Any way to send a small current down a wire to identify it?

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  #1  
Old 06-16-11, 05:07 PM
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Any way to send a small current down a wire to identify it?

I have three individual wires that run from my house to a garage building about 200 feet away. The wires were broken at their midpoint by a tractor a couple of years ago and I'm just now patching them.

One of the wires has a yellow stripe so I can easily match the end of that wire where the break occurred to its other end at the main panel and sub panel in the garage. But, the other two black wires look identical so how do I know which is which?

Is there a simple way to send a small current (like a 9 volt battery) down the wire and then check for it at the other end with a clamp meter?
 
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  #2  
Old 06-16-11, 05:22 PM
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How are you planning on patching it? Were individual conductors in conduit or a cable used, and what type? How deep are the wires buried, and are they gfci protected?
 
  #3  
Old 06-16-11, 05:26 PM
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Justin, I'm all ok with doing the patch from a previous posting I made back when the break happened. I'm using Polaris Blue connectors.

I just need to figure out how to identify the wires. This must be something that telephone and network guys do all the time given how many wires they have to deal with.
 
  #4  
Old 06-16-11, 05:43 PM
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If these are hot leads, and the third your neutral, you won't need to sort them. Both will carry 120 volts to the subpanel. But to answer your question, a signal generator will do the job you want.
 
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Old 06-16-11, 05:49 PM
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Since you already know have one good path, you can use a continuity tester from one end, and connect wire 1 & 2 on the other end, then connect 1&3. With a few permutations, you can figure out which wire is which.
 
  #6  
Old 06-16-11, 06:26 PM
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Zorfdt----that sounds like a good idea since I already know one of the three wires (the one with the yellow stripe). But, I'm not sure exactly how to use a "continuity tester from one end" as you mentioned.

My Sperry DSA-500 clamp meter says it tests for "resistance" and "continuity" so it looks like it will do what you suggest.

I think this is what you are suggesting I do:
From the trench outside (where the wires were broken), I'd twist the yellow striped wire with one of the other two black wires. Then go to the main panel, undo all three wires and touch one probe of the clamp meter to the yellow striped wire and the other probe to one of the two black wires and look for a reading. Whichever of the two black wires gets a reading from the clamp meter is the one that is twisted to the yellow wire out in the trench.

Does that sound correct?
 
  #7  
Old 06-16-11, 06:56 PM
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Yes, but since each wire carries one leg of your 240v it doesn't mater which is which.
 

Last edited by ray2047; 06-16-11 at 08:17 PM.
  #8  
Old 06-16-11, 07:25 PM
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To redefine my earlier post #4, I should have said EACH will carry...... not BOTH. Ray is more correcter than I are.....am.
 
  #9  
Old 06-16-11, 08:15 PM
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But only relative to neutral. To each other it is 240v. Have we confused you enough? {LOL}
 
  #10  
Old 06-17-11, 08:58 AM
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I'm going to try what Zorfdt suggested but it would be nice to buy a device to test each individual wire. I looked at tone generators and Greenlee makes one I've seen for $35. but are those only for small network Cat5 type wires or would they work on heavier AC current wiring as well?

Even better than buying something like this would be to create a simple "signal generator" using a 9 volt battery to use on one individual wire without having to create a complete circuit between two wires. Does that sound possible?
 
  #11  
Old 06-17-11, 10:07 AM
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But as stated there is no need to identify the individual wires if one has a yellow stripe and is used for neutral. Just be sure to conect the yellow stripe to yellow stripe. The other two just connect. No need to identify. Each just carries one leg of the 240v and since this is single phase it doesn't matter.
 
  #12  
Old 06-17-11, 10:16 AM
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From your helpful suggestions I understand that its ok to mixup the two black wires for what I'm doing but I'm thinking of other uses where it would be nice to have such a way to trace a wire when you have only the ends available and you're not sure if the two ends go to the same wire. For instance, I have several unused wires running in my house (doorbell, phone, disconnected electrical circuit), all of which are no longer used----it would be nice to easily and quickly identify each when only the ends are exposed. It would be hard to run new wires in those places where these wires are and I could reuse these older wires for some home automation stuff I'm planning. For example, I don't know of an easy way to know if the wire I'm looking at in the wall of the living room is the same one I'm seeing at the other end of my basement----I think it was an old doorbell wire that no longer has current in it but it looks just like some other wires I'm seeing in other places.

Is there an easy way to send a tiny current down it and then measure that current at what I think might be the other end of that wire? Or, is buying a "signal generator" or "tone generator" the only way?
 
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Old 06-17-11, 10:48 AM
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Connect the nine-volt battery to the two unknown wires noting that one will be connected to the positive terminal of the battery and the other wire will be connected to the negative terminal of the batter. Go to the other end of the wires and by a process of elimination find the two wires that register nine volts on a digital DC voltmeter. When the red lead of the voltmeter is on the wire connected to the battery positive the digital display will read + 9.0. If it reads -9.0 then swap the red and black leads of the voltmeter. You may then mark the wires with labels using a similar label on the same polarity wire at each end.

Example: Mark the wire connected to the battery positive terminal with an A. Mark the wire connected to the battery negative terminal with a B. Go to the other end and when you find the wires that give a reading of +9.0 mark the wire connected to the red voltmeter lead with an A and the wire connected to the black voltmeter lead with a B. Continue for any additional wires using different lettered labels.
 
  #14  
Old 06-17-11, 10:59 AM
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Thanks a lot Furd----that is very helpful.

Now, is there any way to do something like this but with just a single wire?
 
  #15  
Old 06-17-11, 11:28 AM
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If the single wire is in a metallic conduit then connect one battery terminal to the conduit and the other to the wire in question. Use the voltmeter at the other end connecting one lead to the conduit and the other to search for the single wire.

You may also be able to use a bare copper equipment grounding conductor instead of the conduit if one is present.
 
  #16  
Old 06-17-11, 11:56 AM
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What if I have just a single wire that is not in conduit?
 
  #17  
Old 06-17-11, 04:13 PM
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Originally Posted by fromhollywood View Post
What if I have just a single wire that is not in conduit?
You are making this a lot more difficult than it really is. With your latest question, ground one end of the single wire and ring it out with a meter to ground at the other end. Your multi meter is your friend.
 
  #18  
Old 06-17-11, 04:41 PM
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Thanks for the replies. Sorry to make things difficult. That wasn't my intention. I'm still on the learning curve. I've always been told I ask too many questions but I guess I'm the curious type.

I'm not sure what "ring it out with a meter to ground" means but I will figure it out.

Thanks guys. I appreciate your help.
 
  #19  
Old 06-17-11, 04:44 PM
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Ring it out means to impress a signal on a line which can be picked up by a detector. Meter it out to ground means a continuiy check to ground with a meter set to resistance(Ohms).
 

Last edited by ray2047; 06-18-11 at 06:04 AM.
  #20  
Old 06-17-11, 06:33 PM
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You may be able to trace a single wire using a tone generator and amplifier probe. The tone generator has two-wire output. One you'd connect to your wire, and the second to a ground (cold water pipe, etc). The tone generator sends a frequency-modulated current down the wire, which you would use an amplifier probe to 'listen'. Due to induction, all the wires in the conduit may 'ring', but the one that's connected will be the loudest.

To be honest though, I don't think I've ever used a tone generator on a single wire before - so while I believe it will work based on reading manuals, your mileage may vary.

Example tone generator kit:
Amazon.com: Extech 40180 Tone Generator and Amplifier Probe Circuit Finder Kit: Home Improvement
 
  #21  
Old 06-18-11, 04:56 AM
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If you have only one wire, it would be easy to identify. It's the only one there
 
  #22  
Old 06-21-11, 05:12 AM
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An ohmmeter or continuity meter sends a small current down the wire in question. You do need a return path, thus the one wire you know goes between the two locations twisted to one of the unknown wires at the far end. You put the two meter probes on the two wires at the near end.

Always disconnect the power before doing ohms or continuity measurements.
 
  #23  
Old 06-21-11, 08:10 AM
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I have even found a minature christmas light and two aa batteries to work well. Use some scrap wire for a return path.
 
  #24  
Old 06-24-11, 06:41 AM
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Per prev posts you could get a tone generator and filter probe but that's a really expensive way to determine continuity. If I were you (I assume you have an ohm meter with a continuity tester) attach one lead the the meter and grab a long piece of small gauge wire like 24AWG or whatever you have around and tie it to the far end and carry it back to where the meter is. Touch it to the other lead on the meter. If you have continuity you are good.

Thought number 2 if its a long run. Tie one black to the yellow you've id'd and do the same thing.

If you don't have a meter you should get one.

D
 
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