I have breaker that is 20 amps and is a 12 gauge copper wire that leads out of the box. Somewhere along the line in my upper crawl space it connects to a 14 gauge copper wire? What is the best way for me to find out where this connection has been made? Yes?

I have checked my whole house when I been replacing receptacles and switches and even the junction box except for the upper crawl space. What is the best way to trace this type of problem. If you used a multimeter it won't tell you if the gauge of wire is 14 or 12? Is there an instrument for tracing this kind of problem and identifying where the two 14 and 12 copper gauge wire meets--if not what would you suggest. Yes getting an electrician would be last resort but besides that I'm curious on what you guys and gals do when this happens. I'm sure it has to be a wire nut connection somewhere in the upper crawl space. This connection happened some 7 years ago when I had a new box installed but never checked the labeling until recently. This particular breaker actually connects to bedrooms and some hall lights. Thank u Larry

  • 2
    I think you pretty much have to get in there and follow it back. Presumably it's somewhere visible or you would see a patch somewhere.
    – Trevor_G
    Mar 3, 2017 at 2:27
  • 5
    Use a tool like this Tone Generator on the disconnected circuit to help you follow the path. You will need to trace the path of the wire and manually find the transition. -Or- simply downgrade the breaker to 15 amp and mark the wire with a tag that circuit contains 14ga wire so that someone in the future doesn't change it back to a 20 based on "wire leaving breaker is 12ga".
    – Tyson
    Mar 3, 2017 at 2:40

3 Answers 3


Putting this trick first but it is my last resort.

To find wiring when I don't have my scanner, a simple stud finder with a voltage alert. Turn all the other circuits off then using the stud finder watch for the voltage alert to light up. You can get within a couple of inches of the wire path through the walls and figure out where it goes. I have used this method several times where I was not planning on doing any electrical work. It is cheap and works well but you do need to turn the other breakers off for this method to work well.

To answer your question, here are my normal methods to trace wire and find circuit breakers.

I use a Greenlee CS-8000 it injects a signal on the wire and can trace wires through walls and even conduit. This tool is expensive ($995) and not worth it for homeowners.

When I am doing telecom I use a less expensive toner/tracer again made by Greenlee but there are lots of low voltage toner/tracers both of the above can be used with no power on the circuit or live. (The wand style for telecom is limited to phone line voltages not 120 volts.) These need to be in close proximity to the wire to use on 120 v wiring & the breaker needs to be turned off. These are less than $100.

The last circuit tracer I use is the cheapest made to find circuit breakers most of these cost ~60$ and require a live circuit to work you plug into an outlet with the transmitter and use the receiver to find the correct breaker.

  • It appears that all agree that I should use a tone generator or a circuit tester (which I do have). Again. Not sure how to use a tone generator, but willing to try. I agree on your assessment as well including a stud finder. Interesting idea. Mar 5, 2017 at 22:50

If there is any 14 AWG wire in the circuit, the breaker must be 15 amps. Now.

Since this is old wiring, you don't need to comply with current code requirements for 20A circuits in certain locations (e.g. bathroom). The important thing is protecting the 14AWG wire with a 15A breaker.

If at some point, later, you are able to fully investigate and replace all the 14AWG with 12AWG, then you could up-breaker to 20A.


I am guessing the wire goes to a junction box and is wire nutted with another circuit and the circuit was probably added by someone after the home was built. So I would identify what circuits the breaker controls. Then with that info at hand, I might be able to get a hunch as to where there is a junction for those two wires - like say they added a coach light, a porch light or outlet.

You can also use a Tone Generator / Tracer to track the wire down. Your lowes or home depot might carry an el-cheapo that possibly will work for you.


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