Found out my $40 voltage tester was reading false positives for months

I was out on a job downtown last Wednesday, hooking up a new DSC alarm panel in a 3 story walkup. Got to checking the transformer voltage like I always do with my little Klein NCVT-3. It was beeping like crazy on the low voltage wiring. I thought for sure there was a short. Spent almost an hour tracing wire runs and swapping out resistors. Turns out the tester was picking up phantom voltage from a nearby fluorescent ballast in the ceiling. The actual line was dead clean. My buddy Steve laughed at me and showed me his Fluke meter that has a dedicated LoZ mode for stuff like this. Has anyone else had a cheap non contact tester steer them totally wrong like that?

3 comments

3 Comments

benc5322d ago

Yeah that's a classic case of relying on a tool that just wasn't built for the job. Those little non contact testers are great for finding live wires in a wall but they're basically just fancy antennas. Any stray field will set them off even if there's no actual current flowing. Fluorescent ballasts and nearby Romex can totally mess with them. A buddy of mine calls them "ghost detectors" for that exact reason.

rowanellis21d ago

Ha, ghost detectors. I mean sure they can be fooled sometimes but is this really that big of a deal? Every tool has its limits. You wouldn't blame a hammer for not turning a screw. People act like these things are useless but for a quick sanity check they're fine. If you're using one to do actual troubleshooting without a meter that's on you not the tool. It's like getting mad at a level because it doesn't tell you if a wall is plumb through drywall. Just know what it's good for and move on.

skyler_smith8522d ago

Ghost detectors, that's a good name for them. Had an old timer on a job once who swore his tester was picking up "bad vibes" from a wall. Turns out it was just a hidden junction box with a loose splice throwing off a field. He spent an hour tracing nothing while I found the actual problem with a meter in five minutes. Made me appreciate a good multimeter even more.