Isolating a specific electrical cable

Stan in Oly, WA

Well-known Member
Is there a simple, non-destructive way to find out whether a 12/2 W/G electrical cable in a house is carrying current? I need to find a run of cable on a particular circuit in my awful crawl space. It would be much simpler if I could just turn off that circuit at the breaker and find the cable not carrying current. The alternative will be to start where the cable drops through the floor from an outlet I know to be on the circuit I want, then follow it back to the point where I need to tap into it. But that means starting on the far side of the house in a crawl space which is too low to get around in on hands and knees, and trying to follow cable which is concealed by fiberglass insulation between the joists. I used to not hate this kind of project, but those days are past.

Stan
 
(quoted from post at 22:38:55 09/10/18) Is there a simple, non-destructive way to find out whether a 12/2 W/G electrical cable in a house is carrying current?
Yes, there is. You'll need a tool like this:
https://www.amazon.com/Fluke-1AC-A1...&sr=8-3&keywords=fluke+voltage+tester

There's 2 ways you could go about it. You could turn off the breaker you want to find, then check to see which wire isn't powered. The other way is to turn off all circuits that you DON'T want to find, leaving power only to the one you're looking for. Then go and check for a powered wire.

The difference between these methods is, if there happens to be a wire that is not connected or is no longer used, but still exists, then you might erroneously choose the wrong wire if you leave power on to all circuits except the one you're looking for.

As a safety, once you find the wire in question, do a reverse check - turn off power to that wire, then check for power. If there is still power, you know something ain't right!

This is a very valuable tool to have any time you work with electrical wiring, as using it helps prevent the chance of getting electrocuted due to carelessness, simple mistake, or outright bad wiring job.
 
A way is to use a clamp on amp meter. You do not have to damage the insulation in any way. you just need to be able to get completely around the wire with the clamp. It has to close to read correctly.

I use one pretty regularly. I hate working on stuff that some one has "probed" with a sharp probe. Ruins the insulation.
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Get yourself a non-contact voltage sensor. I am partial to the Fluke but Klein makes a decent one also. You can get them at Lowe's or Home Depot for under $30. You will wonder how you ever lived without one. You simply hold it up to a wire and if there is AC voltage present it will beep and flash a red light.


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The problem with a clamp-on meter is you have to clamp it around a single conductor. You can not clamp it around a sheathed pair of wires. Also, it is for measuring current (AMPS). The circuit the OP is testing may not have any loads on it. PS: I know the OP used the word "current" which would be AMPS but I think he really meant to say "voltage". Unfortunately a lot of folks use the word "current" when talking about household AC wiring and it can make things confusing. :)
 
I?ve been locating and tracing wires most of my life. There are toners that phone and cable tv techs use but you must remove the voltage from the wires before use in most cases. There are as many kinds of locators as there are prices of locators. From a few hundred to thousands of dollars. For what I?m hearing you say I?d look at the link below. It?s made for your project. But for a one time use it is pricey. So I guess it will be a trade off comfort (spending money on a new tool) vs crawl space (saving the money and crawling on your hand and knees). By the way, you can trace the wire though the floor with this machine. So you can do most of your tracing out of the crawl space.
Wire locator
 
Our fire department came out to help find a hot wire smell in our house. They had a heat finding deal and showed every current carrying wire in our walls. They found a slightly loose lug in one of our service boxes that caused a wire going to a bathroom receptacle where Dixie had a hair curling brush thingy plugged in with the switch on to get hot. Where there were several wires running thru a wall, the screen on their heat checking deal the higher the load the brighter the wire was on the screen. They were in and out in minutes.
 
Stan,

Can you get to the end at the breaker box? If it were me, I would lift the hot wire at the breaker and use a circuit tracer such as the Fox and Hound by Triplett to trace the wire. Attach the Fox at the end of wire you disconnected from the breaker and use the Hound to find it under the house. You can get the Fox2/Hound3 online or other generic circuit tracers from Home Depot or Lowes for about ~$80.

Triplett makes a more expensive "Hotwire" version that will work on live AC circuits if you cannot get to the breaker panel to shut it off. More like ~$150, but you can clip it onto the hot wire anywhere and trace it back with the Hound. This sounds more like exactly what you need.

Hope this helps.

Cliff(VA) soon to be (NC)
Fox and Hound Hotwire
 
You say you need to tap into the wire? As in cut and splice into it?

That is not a good practice to have a splice in an inaccessible area. Usually not enough slack to make the splice in an enclosure.

Couldn't you just run a new wire from one of the outlets, down through the floor to where you want the new outlet?

Or am I not following the question?
 
I've got a gadget that I bought when we needed to identify circuits in our church. It's designed to plug a signal generator in a live outlet and take the signal tracer to the breaker box to find the correct breaker for the circuit in question. Flip off the identified breaker and the signal goes silent. I've also used it to trace circuits in attics. The tracer will sound anywhere along the live circuit. I'm not sure how the insulation would affect your search - I've never used it when the wires were covered by insulation, so not sure of the range away from the wire. I think this thing cost around $40 about ten years ago. I can't remember the name, but if you're interested I'll dig it out and get more info for you.

One of the little pencil proximity testers would work if you could kill every circuit but the one in question. Some of them are hotter than others. I have two, and one needs to touch the cable sheath before it beeps. The other one sometimes beeps before I pull it out of my shirt pocket. Both are handy for different reasons.
 
Steve; You're following the question correctly. I struggle to keep my posts reasonably short because I'm inclined to want to explain more than I need to. I wrote "tap into" the line because my question was about how to find the line, not how to make the connection. I would put in two accessible (to the extent anything in my crawl space is accessible) junction boxes so there would be no need to try to make any connections with too little wire. I think it's fairly likely that I'll find the line I need in the general area of the new 12/2 cable I dropped through the floor because that's on the path to the electrical panel. The other way of doing it---taking my power from one of the outlet boxes above the opposite side of the crawl space---would be a difficult job even with an experienced helper, and I'll be working alone. And then there's the problem that every cable staple I would use to secure the new line to the side of a joist would require me to move insulation.

I appreciate knowledgeable observations, though, because people sometime bring up issues I didn't previously know about. Thanks.

Stan
 
Harbor freight sells a cheap circuit detective. You plug in the transmitter in an outlet and then take the receiver to the breaker box and it will tell you which breaker that outlet is on. Then shut off all the rest of the breakers and you would be able to tell which wire is hot in the span between the outlet and the breaker box with a non-contact voltage tester.
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(quoted from post at 09:10:22 09/11/18) I struggle to keep my posts reasonably short because I'm inclined to want to explain more than I need to.
Join the club. I could probably write 3 or 4 chapters (unknown paragraphs!) just to say it's hot outside. :roll:
 
(quoted from post at 22:19:54 09/11/18)
(quoted from post at 09:10:22 09/11/18) I struggle to keep my posts reasonably short because I'm inclined to want to explain more than I need to.
Join the club. I could probably write 3 or 4 chapters (unknown paragraphs!) just to say it's hot outside. :roll:
ife always tells people, "don't ask him what time it is....he will explain how a clock works!"
 
I want to thank everybody who responded to my question. Several of the devices suggested here would have done the job, but the easiest thing in my situation was the non-contact voltage tester. I would have been glad to pay the $30 or so that Home Depot (or Amazon) wanted, but Harbor Freight had one for $5.69 and the reviews of it all said it worked as well as a reputable brand. I got one and it did. It solved the problem.

I'm sure not as good at crawling around in that crawl space as I was fifteen or twenty years ago. It seems like it's
gotten longer and wider and lower. You don't notice it so much in the house.

Stan
 

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