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I have an GFCI outlet box wired with yellow coated wire, which I believe goes to a dedicated circuit breaker. When I turn off the breaker to the box, I still read residual voltage. Is this induced "phantom voltage"? Is it safe?

This outlet box is underneath a jetted tub, so I want to be sure there is no voltage in the box when I turn of the circuit breaker.

The 3 tools I used to measure the voltage are:

1) Gardner Bender GDT-3190 multimeter (10 MOhm input impedance) - when pluged in to outlet hot and neutral, multimeter reads 2.1V on 200V AC setting.

2) Klein Tools NCVT-2 proximity Voltage Tester - when close to the yellow wire, tester beeps for voltage reading on 12-48V scale, but not for 48 - 1000V scale.

3) SPERRY GFI6302 outlet tester - reads open hot, so not picking up any voltage.

Thanks for the help!

resident
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    if you plug in something small, say a night light, do you still read 2.1v? if not, it's probably not deadly; an induced current. if it does still have voltage, you need to get someone out to check it out. – dandavis Nov 03 '17 at 20:51
  • The #1 tool you used is probably the best, and ~2v is very low. That's like AA battery range, and probably phantom. – JPhi1618 Nov 03 '17 at 21:01

2 Answers2

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Using a Digital meter you can pick up phantom voltage fairly easily - an analog meter typically not so. Reading 2.1V is typical of a line that crosses any other circuits. Regardless of that reading - ALWAYS work on the lines as if they are hot! You never know who has done what - if the home was owned by someone else - maybe they did something 'creative'. Even some ' pro's ' if they are not followed up on might do something that maybe it is in code but not really what should be done.

Now it sounds like you are replacing that GFCI outlet- make sure you follow the instructions of the new GFCI outlet - your neutral is very important - of course so is your ground. Connect them correctly. In the USA White is neutral, black is hot and green (or un-insulated copper) is ground. The color of the Jacket that contains all three wires is not of any significance.

As an FYI: Your yellow wire as you call it ... You should have what is often called Romex wire - which is a collection of conductors each insulated in their own insulation material (in their own colors.) All contained with in a jacket assembly. See an example at this link.

https://www.homedepot.com/p/Southwire-1-000-ft-12-2-2-Solid-Romex-SIMpull-CU-NM-B-W-G-Wire-55048401/202528018

Ken
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    Thank you for the response! I bought a Fluke 117 multimeter and measured 3.6V on the V AC setting (input impedance = 5MOhms) and **0.2V on the LoZ setting** (input impedance = 3kOhms) between neutral and hot. So I am assuming this is phantom voltage. – resident Nov 06 '17 at 01:00
  • @resident the LoZ is a good place to read your voltage with a DMM ..it is just phantom voltage .. I work on ac lines as if they are hot even when I know it is not hot, this can save you trouble at times. You might for example think that a schedule label : receptacles room 2 means all receptacles, but instead only 3 of 4 are on that breaker.. sometimes getting in a hurry you might check a couple or three of them and assume - don't assume. Also you might be working and someone in the home decides they found your breaker off and go DUH. lets turn it on.. – Ken Nov 06 '17 at 18:38
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With AC, you may get phantom voltages as wires pick up signal from other wires adjacent to them. When measuring power circuits, a low impedance multimeter is often used. This basically draws a rather large current for measuring voltage - which is the opposite of what we want with a voltage measurement in circuit.

You can make your own low impedance multimeter, by connecting a normal incandescent light bulb in parallel with your probes, for instance to the same outlet as you are measuring. You can not use a LED lamp, or fluorescent, but any incandescent light or other ohmic load (e.g. toaster) will work.

If you are unsure, do not work with electricity. You ever only had one heart.

vidarlo
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