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other50V measured on wire even when disconnected at both ends (self.DIY)

submitted by 404_not-found_

Question in title. Wiring a switched light in a ceiling box that has been capped for a while and when measuring the switched circuit I always have 50V if on or off. At first I thought it was a faulty switch but I tried 3 with the same issue. Then I just unwired the switch and have a my wire connected to load in the ceiling, both ends disconnected at the switch (wire sticking out at the wall), and when i measure the switched load to neutral in the ceiling it’s STILL 50V. Struggling to troubleshoot where this is coming from

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[–]kugelvater 7 points8 points  (0 children)

It could be induced voltage if the wire is running parallel to a current carrying conductor

[–]fredsam25 1 point2 points  (0 children)

Google ghost voltage.

[–]TemporaryBoyfriend 1 point2 points  (1 child)

Can't believe I'm the only person saying this... But maybe the switch isn't broken, and the wire doesn't go where you think it goes, and is connected to something else? I lived in a really old house (1920s/1930s, on the cusp of electrification) when I was a kid, the nothing made any sense about how the house was wired.

[–]404_not-found_[S] 0 points1 point  (0 children)

I did validate the wires were what I thought and disconnected on both ends. I could see it in the attic and down through the wall. “Shake test” confirmed nothing crazy going on for what wire was going where. Based on still getting 50V even when nothings tied in made conclusion it was induced.

[–]nixiebunny 2 points3 points  (0 children)

Voltmeters are high impedance. They will read a substantial voltage coupled capacitively from an energized wire next to the wire you're measuring, if the two wires are in the same cable. Connect an old fashioned incandescent light bulb to the ceiling wires and see if you still get 50V.

[–]Diligent_Nature -1 points0 points  (6 children)

It is not uncommon. Your meter probably has 10 million Ohms input resistance. Wires can pick up electricity from adjacent wires. It is safe because the current induced is very low. Some meters lave a low impedance mode to eliminate this ghost voltage.

[–]RnDanger 5 points6 points  (4 children)

Please don't tell people voltages are safe when you don't know their source

[–]Diligent_Nature 0 points1 point  (3 children)

It is safe in that it doesn't mean there is something wrong. OP stated that both ends were disconnected. Capacitive coupling between wires is the source.

[–]RnDanger 1 point2 points  (2 children)

You could give them a way to test that safely if you think it's true. I don't feel good assuming anything is safe or correct with mains until I verify it, especially when I'm not even with the problem and I've never met the person diagnosing it.

[–]Diligent_Nature 0 points1 point  (1 child)

As I said, some meters lave a low impedance mode to eliminate this ghost voltage.

[–]RnDanger -1 points0 points  (0 children)

you didn't say they should measure it differently, you said other tools exist. (I am happy being a stickler about this because mains voltage is dangerous and this person may be a novice)

[–]umiotoko 1 point2 points  (0 children)

I ran into something similar in an older house, early postwar black Romex wiring. Two wire, no ground and consistently got ~50 volts on the neutral to plumbing ground. A whole rewire was out but checked all accessible connections and put GFCI outlets in, didn’t have any issues with tripping so I called it a day there.

The trick with the low impedance testing is cool, I’ll remember that for next time.

[–]Nice-Mode-8585 -1 points0 points  (0 children)

Measure the voltage between neutral and ground you may have voltage on your neutral?

[–]an_onanist 0 points1 point  (0 children)

Is it possible to wire runs from the breaker box to the light before going to the switch? Try flipping the breaker see if that removes the voltage from The Wire