1

I moved in to a new apartment a couple months ago and noticed one of the LED light fixtures never really turned off, there was always a faint glow from it. Today I went to install some smart dimmers inside the fixtures to connect the to my Philips Hue lighting system. Unfortunately I dont have access to the load centers, so I had to just shut off the light fixture at the switch, work carefully and hope for the best. Before running some additional wire in to the fixtures to acommodate the dimmers, I decided to hook up a multimeter and see what was going on since the light never really turned off. To my surprise I read that the hot to neutral voltage was 65 volts, and the neutral to ground voltage was 124 when the circuit was supposedly off! What is going on here?

How it was wired, ground was never connected: How it was wired, ground was never connected

Hot to neutral reading 65 volts with the switch off Hot to neutral reading 65 volts with the switch off

Neutral to ground reading 124 volts with the switch off Neutral to ground reading 124 volts with the switch off

  • 2
    If this is a rental, bring this to the landlord's attention..... many places have laws against renters doing electrical work in their unit. – JACK Oct 21 '20 at 1:06
  • 2
    Check at the switch. That will tell you for sure whether you've got neutral switched (because the wires at your switch should be hot, so you should get ~120 to ground (switch box) and if you get close to 0 then you know that's neutral being switched. That will also let you verify the color of your switched "hot" (whether it is hot or neutral). I'd also suggest checking all your receptacles with a magic 8-ball (easier than a multimeter for a quick test) to see if they're normal or reverse. – manassehkatz-Moving 2 Codidact Oct 21 '20 at 1:45
  • 1
    Regarding your request to check at the switch, it looks like they're probably switched neutral, colored wrong and the fixture was wired backwards. One of the wires to the switch is white and the other yellow. I didnt really want to undo the wirenuts to check for certain, since the wiring is live and if I blow a breaker I dont have the means to reset it. I have one of those magic 8 balls and will certainly take your advice. – Matt Oct 21 '20 at 2:57
  • Did the old switch have a "night light" so you could see it at night? In the past (incandescent days), a tiny neon night light could run a tiny bit of current thru the fixture to power the night light and not affect the fixture. With LEDs being so efficient, that strategy doesn't always work right. Also, older dimmer switches didn't always have a very "positive off" and allowed tiny bits of current thru, again affecting LEDs. – George Anderson Oct 21 '20 at 11:52
  • Nope, no night lights on the switches, and there isnt any dimmers either, just a 3 gang box with one disconnected switch and two switches jumpered together switching neutral. – Matt Oct 21 '20 at 13:37
3

You used a high-impedance digital voltmeter (DVM), which can pick up induced or capacitively coupled current from nearby wiring. Put a resistor, perhaps 470 kilohms or 1 megohm, across the leads, to effectively "short out" the very low coupled voltage.

  • 2
    The meter (Fluke 117) has a low impedance function (Auto-V/LoZ - fluke.com/en-us/learn/blog/digital-multimeters/…). When measuring it with that, hot to neutral is 0.1 volts with the circuit off, and neutral to ground is still 124 volts. So whats going on here, is neutral being switched, and the wiring colors are wrong and it was wired backwards? imgur.com/a/fiNaAKU – Matt Oct 21 '20 at 1:23
  • 1
    It could be that the switch was placed in the neutral line... not good! As you surmised, the wiring should be checked... and be extremely careful, in the meanwhile! – DrMoishe Pippik Oct 21 '20 at 4:08

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.