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I have 12V AC landscape lighting. Some of the lights are not turning on, so I got one of these 12v AC non-contact testers to try to determine if the cables have been chewed through, etc.: https://www.homedepot.com/p/Klein-Tools-12-Volt-to-1000-Volt-AV-Dual-Range-Non-Contact-Voltage-Tester-NCVT-2PR/312649969?cm_mmc=ecc-_-THD_THANKYOU-_-V1_M1_CA-_-Product_URL&ecc_ord=W878088347&em_id=60b46fbe3a00a750b6b15514e556881a8d75050aa0be1f6cf69d349fac9c8867

However, even on some of the cables that are working, the device doesn't alarm (when used following the user manual and on 12v mode). I read that this could happen when the cables are shielded. Assuming this is the case, what is one to do? I didn't have any luck searching for similar devices that work with shielded cables.

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  • You may just have to go to a multimeter, which is quite safe when dealing with 12V instead of 120V. Nov 21 '21 at 20:51
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    But then it’s not non-contact, and I’d have to cut into the (potentially not broken) wires to measure, right? Nov 21 '21 at 21:06
  • All true. The idea would be to power it up and check at each endpoint or socket or whatever until you narrow down the problem. No simple answer. My hunch is that the 12V is, in addition to being at the low end of the voltage range, using so little current that the whole thing is hard to detect. Nov 21 '21 at 21:11
  • Note: HomeDepot links can't be seen by international users, so pictures & a general description of the info in the link would help. [Also, if the link goes dead in future - e.g. next time they change the site presentation, there's no question left to answer].
    – Tetsujin
    Nov 22 '21 at 8:11
  • it doesn't make sense to shield landscape wiring cables.
    – dandavis
    Nov 22 '21 at 18:03
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Not gonna work.

Electrical appliances don't run on voltage. They run on voltage difference.

Here's a relevant example. Suppose your transformer puts out +6V and -6V (that is to say, opposite phases). The non-contact tester wouldn't detect anything at all. But there would be 12V between the two wires which is exactly what the lights want.

See, current flows in loops. It's well and good for hot power to go out to an appliance, but if neutral doesn't come back, then your appliance will not work. And you see the problem? Neutral is supposed to be near 0 volts, so a non-contact tester won't detect it.

This is why non-contact testers are not useful for wire fault tracing Their job is to detect dangerous voltages, to warn you in advance that a wire is "hot" before it kills you. Its value in a 12V system is rather limited since nothing there will kill you... and I would expect poor performance anyway because 12V is on the bottom edge of its detection range.

To hunt down a broken wire, you need a toner, which injects a high enough voltage and frequency to be seen by a matching non-contact detector.

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