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I have a "dead" line wire in my GFCI outlet. What now? Answered

I used a tester to find the line wires in my GFCI outlet.  I have a live black wire but both of the white ones are dead.  Does anyone have a suggestion or do I need to call an electrician?




2 years ago

Voltage is always a differential quantity, meaning how much between 2 points. That is why a voltmeter always has 2 probes, not one. The black is often considered the common, or ground. It is what all other voltages are often compared against.

-Max- this is important !

In USA house wiring BLACK is Not a common or ground

but it is always the dangerous HOT BLACK wire !!!

I am referring to the multimeter itself, in my last post I did point out that black is the live. Regardless thanks for explicitly pointing this out in case this was not clear to any other readers.

The white colored wires are supposed to be "dead", so to speak. The black colored wires are the only ones that should be "live". So what you have described is consistent with an outlet I would expect to be working.

By the way, these GFCI outlets have a tiny circuit breaker inside. If one of these outlets is not working, it may be because that little breaker has been tripped. The way to reset this breaker, is to push the little button on it labeled "reset". If it resets successfully, then the outlet should work.

The button labeled "test", is there so you can intentionally trip the breaker, to turn the outlet off, or to test if the ground-fault sensor is working.

In summary:

Push "test": Click! Outlet turns off.

Push "reset": Click! Outlet turns back on again.

If an outlet of this kind is not working, the little buttons on the front are a good place to start, just to check if the breaker inside has tripped off.

I apologize if any of this seems obvious.

I would enlighten Sherry about what the GFCI does to protect carbon based living beings from lethal electrical shocks.

There is an electronic circuit inside the GFCI that monitors if the current flowing through the black wire is the same as the current flowing through the white wire.

Should there be a difference of current between the wires there is a possibility that difference of current is flowing through a person and the GFCI immediately disconnects both sides of the power line (ie the black and white wires) !!


2 years ago

What wires are neutral, and should be at the same potential as earth ground. You can even lick those and you would not be in any danger. (not saying you should though!!!) The green or bare wires are almost always earth ground, again, perfectly safe. It is the black wires that carry a voltage with respect to both ground and neutral. Only difference between the neutral and the earth wire is that current is not allowed to flow through the ground wire, and if it does, it should trip the GFI.


2 years ago

Very difficult to understand how a tester can detect a live black wire without the white wire to measure voltage against.

What I'm saying is, you really need an electrician, who I'm sure, also understands how to use a tester...

A non-contact voltage tester can do this. You have probably seen one of these before. If not, here are some pictures of "non-contact voltage tester",


It has this little plastic tip, and the tip lights up when it is in the presence of alternating electric field.

This might be the kind of tester OP is using. Just a guess.

I take it you are testing black to ground and white to ground.

Well white is connected to ground at your service so you should not get a voltage testing white to ground.

If you are testing between white and black or black to ground you should get a voltage.

How a GFCI works is it compares the power coming in on black to the power going out on white. If any of the power goes out on ground there is less power going out on white, and there is a short in what you are using, this should pop the GFCI faster than blowing a fuse.

Stay save and call a sparky.
Not worth risking a house fire or electrocution to save a few bucks.