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One of my home's 120v circuits measures:

  • Line to neutral = 120v
  • Line to ground = 52v
  • Ground to neutral = 45v

What should I look for to resolve this issue?

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  • 2
    disconnected wires
    – jsotola
    Aug 21 at 19:27
  • 3
    those have to be phantom readings with virtually no current, otherwise it would be on fire.
    – dandavis
    Aug 21 at 20:14
  • Solenoid voltage testers don't give you phantom readings. Go big, go home, or go die.
    – Mazura
    Aug 22 at 22:01
10

Open ground somewhere. Digital multimeters are very sensitive and the tiniest of leaks can mislead you. Best to put some sort of small load (like a 25 watt incandescent light bulb, NOT LED) across the line to ground and ground to neutral...separately of course and see what happens. To be fully safe, you'd need to buy a 3 prong (grounded) plug, some wire and connect it to a bulb socket, one time from line to ground for the first test, then ground to neutral. I'd be really surprised if the bulb lit up at all. Most likely the voltage across the bulb will drop to nearly zero in both tests. Phantom, induced voltages are common when there are loose or missing connections and can be very misleading. If the bulb didn't light up and the voltage dropped to close to zero during your tests, all you can do is check every device (outlets, switches and fixtures) on that circuit for a disconnected ground wire. If the bulb lights up, I don't have a clue what your problem is!

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  • 8
    It may be simply that the ground socket on this outlet was never connected. Perhaps a previous owner installed a three-pin receptacle in a box that only had a two-wire cable.
    – CCTO
    Aug 22 at 4:38
  • 1
    @CCTO Indeed, I'd start by making the wires on the receptacle visible. A missing wire would be a giveaway.
    – Mast
    Aug 22 at 12:10
  • The light bulb test showed no light and close to zero voltage. I will inspect the receptacle box but it and the other one in the circuit are blocked by heavy cabinets. Looks like I will need to make them accessible.
    – Michael
    Aug 22 at 16:41
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    I can't say I'm a fan of the idea of deliberately placing a low impedance load between live and a known-dodgy ground, thereby making anything connected to said dodgy ground live. Aug 22 at 18:04
  • @PeterGreen I thought about for quite some time before posting my answer.Maybe I should have included in my answer to be careful around other grounded appliances on that circuit. But I felt the risk was minimal enough not to include the warning. But I respect your comment. + Aug 23 at 1:20
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It's a side effect of DVMs (which includes most cheap meters). They're so sensitive (so high impedance) that they see "float voltages" on entirely disconnected wires, which are merely from capacitive coupling of nearby wires. There is no current behind them.

Any actual load will tamp down that phantom voltage. With 120V/230V you don't want to fool around with putting resistors across test leads, so stick to plug-in loads. Most of those only load hot-neutral... but a common, cheap 3-light tester will place loads across all 3 sides.

enter image description here

On most of these, the 3 lights are marvelous, but I call them "magic 8-ball" testers because the label explanations are misleading and waste hours of your time. (they're tuned for wiring errors in new construction, not wiring failures). This one has a less misleading label.

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  • Harp: I agree with most everything you said, except for the common misuse of the term "capacitance". It's inductance. Wires/cables aren't capacitors. Aug 23 at 1:24
  • @GeorgeAnderson: It's not possibly to inductively couple to an open circuit.
    – supercat
    Aug 23 at 9:35
  • @supercat True, but It may be a open circuit for now, we don't know yet, but the voltage potential is there. I know that personally because I got zapped pretty good a few times helping a master electrician at my church doing some re-wiring. Got a reading of 170 volts on a circuit that was turned off. I put an incandescent light bulb across the circuit and it dropped to almost zero. Aug 23 at 12:04
  • "It's not possibly to inductively couple to an open circuit" Isn't that exactly what a transformer is?
    – Duston
    Aug 23 at 14:05
  • @Duston: The two ends of a transformer secondary are necessarily conducted by a current path (the secondary coil).
    – supercat
    Aug 23 at 14:53
3

look for loose/broken connections, it may be located at a different point in the circuit than the receptacle you are looking at. Also make sure there is nothing else plugged in anywhere else on the same circuit when you are checking voltage, that can rule out a faulty appliance causing the issue.

If the problem goes away when nothing is plugged in then the wiring is likely fine and something that is plugged in is at fault. I would go this route first as it is easier than ripping everything apart.

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As long as you're checking voltage, the next logical step is to simply remove the outlet cover, visually inspect the connections, and test the voltage on the screws. When finished, you can safely reset the cover. I believe this is much more likely to reveal potential causes of any problem than by fooling around with lamps and grounded loads.

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