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I have an exposed wire coming out of a wall, I believe the old owners of the house had a wine fridge or some other appliance installed in the space. I went to install an outlet on this wire and measured the voltage with a Klein Tools MM400 multimeter. When I measured the AC voltage, I measure about 12 V at 3 kHz.

Of course, thinking I wasn't measuring it correctly, I measured some other outlets with the same settings, and every single outlet measures 120 V at 60 Hz, exactly as you would expect.

What could possibly cause this reading?

The house has a solar PV system, but nothing from that system wires into this side of the house. The PV inverter is on its own breaker, so I don't see how this could be from the PV system (maybe I'm wrong).

The house also has an electric car charger that is wired into the circuit breaker cabinet in the garage, but it also has its own circuit, so I don't see how that unit could create any interference either.

I'm at a loss on this and would appreciate any insight on this. I'm requesting an appointment with an electrician, but I'd like to here what stackexchange thinks about it.

UPDATE Based on some other posts I was reading, I did some more investigation.

  1. The above reading was line-to-neutral, I measured the current and I get 365 mA. Now that it is morning and the sun is out, I'm measuring 12 V at about 10 kHz. I suspect that this is capacitively coupled noise from my PV inverter as this equipment uses a PWM driver for regulation, and they tend to operate at low kHz frequencies.

  2. When I measure line to ground, I measure 120 V at 60 Hz with 2.5 A current. Measuring neutral-to-ground gives 0 V.

UPDATE 2

While turning off breakers to start searching for a loose connection, I found that my problem wire is connected to a dedicated breaker, there is nothing else connected to the circuit. Apparently I was mistaken about where the line starts.

Since this is the case, I'm assuming my open neutral connection is exactly at the breaker. I suppose it's unsafe to just cap the neutral line and bridge the ground copper to the neutral screw and the ground screw on the new outlet...

For reference: Electrical: Can a neutral wire just be capped?

sparaps
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  • A long discussion about odd voltage readings here: https://diy.stackexchange.com/questions/232372/strange-voltage-at-receptacle/232440?noredirect=1#comment445245_232440 – Duston Aug 24 '21 at 15:02
  • Thanks @Duston, that was very helpful, please see my update above for more info – sparaps Aug 24 '21 at 15:47
  • Do you have continuity neutral to ground? – manassehkatz-Moving 2 Codidact Aug 24 '21 at 16:01
  • @manassehkatz-Moving2Codidact no, they aren't connected, I measured between neutral and GND with my DMM and I measure 0 V, so they appear to be at the same potential, but they are not connected directly. – sparaps Aug 24 '21 at 16:14
  • Neutral and ground are connected in one spot usually main panel. If everything is connected properly then you should get 0 (or very low) ohms neutral to ground elsewhere in the system. That's ohms not volts – manassehkatz-Moving 2 Codidact Aug 24 '21 at 16:18
  • @manassehkatz-Moving2Codidact I see, I misunderstood what you mean, I measure an open circuit between neutral and ground. – sparaps Aug 24 '21 at 16:28
  • Sounds like your neutral is not connected properly. **NOT safe** – manassehkatz-Moving 2 Codidact Aug 24 '21 at 16:40
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    Thanks for the update, I wrongly assumed the 12 V were relative to ground. I have deleted my dangerous answer. – TooTea Aug 24 '21 at 17:40
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    @TooTea good thing I didn't start playing with it! It's sounding like this is a bad neutral connection, would you agree? – sparaps Aug 24 '21 at 17:48
  • "When I measure line to ground, I measure 120 V at 60 Hz with 2.5 A current" - How *exactly* did you measure that current? With pictures of the meter connections, meter settings, and readings. You can't measure current between two points like that (and shouldn't try) - you must measure current in series with a load. If you put your meter across actual line and ground or neutral, you create a nearly dead short circuit that will either blow the fuse in your meter or actually blow up its circuit board. There may also be quite a spark at whichever probe makes contact second. – nobody Aug 25 '21 at 02:21
  • _I suppose it's unsafe to just cap the neutral line and bridge the ground copper to the neutral screw and the ground screw on the new outlet..._ You assume correctly. **DO NOT DO THIS** Ground should _NEVER_ be connected to neutral _anywhere_ in your wiring (except at the _main_ panel, never in a sub-panel). – FreeMan Aug 25 '21 at 12:59

1 Answers1

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Bad Neutral

Figure out what else is on the circuit. There is likely a loose, or bad backstab, neutral connection.

Definitely not safe to connect anything until you get a good hot/neutral reading. Do not bootleg neutral to ground - it will work but cause very unsafe conditions in the rest of the house.

According to comments, this is fed by LOAD of a GFCI/receptacle. If checking/reconnecting those wires does not solve the problem, pigtail the wires to LINE instead of LOAD. If that works then you have a GFCI issue. If that does not work then you have a bad wire (e.g., nail through a wire in between the two ends).

manassehkatz-Moving 2 Codidact
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    I can see exactly where this line starts, it comes off of another duplex GFCI outlet that is coming out of the wall about 4 feet directly above my wire. That upper outlet is working properly. Maybe I just have a bad connection on the load side of the other GFCI outlet? – sparaps Aug 24 '21 at 17:24
  • That's what it sounds like. Are you using backstabs or screws? If backstabs, move to the screws. – manassehkatz-Moving 2 Codidact Aug 24 '21 at 17:46
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    I will have to open up that outlet and look... – sparaps Aug 24 '21 at 17:47
  • My problem line is on a dedicated circuit with its own breaker, it has nothing else connected to it. Would it be possible to just cap the neutral line and connect the ground to the neutral screw directly on the new outlet? For reference: https://diy.stackexchange.com/questions/74091/electrical-can-a-neutral-wire-just-be-capped – sparaps Aug 25 '21 at 04:57
  • You can cap a neutral when you have a hot/hot/neutral/ground cable and the neutral isn't needed. But you have a hot/neutral/ground situation, so that doesn't work. In addition, you can't swap ground for neutral. While technically (assuming it is an insulated ground) it would *work*, it would not be to code. Code requires bare or green wires to **only** ever be ground and only white or gray for neutral. You might be able to wrap every inch of the wire with white tape - but it would be a whole lot easier to replace the cable. And most of the time the problem is at one of the ends & easily fixed. – manassehkatz-Moving 2 Codidact Aug 25 '21 at 05:00
  • How do you know it is totally dedicated and not passing through some other receptacle or junction box in another room? – manassehkatz-Moving 2 Codidact Aug 25 '21 at 05:02
  • I'm reasonably sure, I checked every outlet on that floor with the breaker turned off, all other outlets were still on – sparaps Aug 25 '21 at 20:47
  • Could be on multiple floors (some of my circuits do that) and could also be shared with some lights (some of mine do that too). – manassehkatz-Moving 2 Codidact Aug 25 '21 at 22:25