Two pronged outlets

The standard is that they can be changed to a GFCI outlet. When they are changed to a GFCI outlet and I put my outlet tester in it, the tester shows no ground (which is good), but is the GFCI supposed to trip when I try to trip it?

Should trip when you press the test button on the outlet, but it won’t trip if you use your little outlet tester thingy. (Hope my description isn’t too technical.):wink:

GFCI’s trip 2 ways.

Hot to Ground and Hot to Neutral.

Basic GFCI Testers only Test the Hot to Ground…

Huh? Sorry, no.
The two you just mentioned will create a direct short and trip the breaker, not the GFI.
A GFI is tested neutral to ground.

In a “no-ground” situation the test button on the device will work, but theplug in testers will not.

edit - sp. typo

How does a GFCI Tester test Hot to Ground if there is no Ground?

A GFCI receptacle, new or old, can’t trip with a plug in tester unless there is an EGC connected to the GFCI. There is no path for the test current to flow on without an EGC. When testing GFCIs with the internal test button, you must test for voltage on the GFCI receptacle after you push the test button. A GFCI receptacle that has the power connected to the load terminals will still have power( on older models) on the receptacle even when the button shows that the device has tripped.

The GFCI works because it detects the difference between the grounded and ungrounded conductor.

Here is a nice little article on it…I did not write this…


    GFIs and GFCIs are Ground fault interrupter and Ground faultcircuit interrupters. The ground fault interrupter is a receptacle that has the ability to open or disconnect the power from the output of thereceptacle. The ground fault circuit interrupter is a breaker that hasthe ability to disconnect the power from a circuit.        The ground fault senses a difference in the flow of current fromthe hot wire through the neutral, if that difference is about 5 milliampsor more the ground fault will trip the circuit out. It accually assumesthat if the current is not flowing in the neutral it is flowing throughsomething else. Some motor windings have sufficient losses to cause oneto trip out so don't use a gfi circuit for a refrigerator or washer outlet.You should use(and the NEC requires) the use of gfi protected outlets within6 feet of a sink, anywhere in a bathroom, in a garage or outside; anywherean outlet can be reached from a water source, a wet area, or earth ground,you should use gfi protection.        A gfi receptacle has a line side (incoming power) and a load side(outgoing power). The receptacle will not work if the incoming power is connected to the load side of the receptacle. Connect the incoming powerto the line marked terminals and the continuation of the circuit (the nextoutlet) to the load terminals. The one gfi will protect all the followingplugs or receptacles connected in this way. Even if you don't have a continuation of the circuit, connect the power to the line side of thereceptacle.        Gfi recptacles and gfci breakers have a test button that shouldcause the circuit to trip, operate the test button after installing and regularly there after to be sure it works properly."

The first part is in reply to the statement made in the quote referring to how a GFI trips.

The second part I wrote is in relation to the “no-ground” situation. Which is why I put “no-ground” in quotes.


If a GFCI only detects a fault to ground, why is a GFCI recommended to be installed in a circuit where there is no ground?

So my tester should show no ground, the tester will not trip the outlet but the test button on the outlet should trip the out let? Anything else?

It will still trip if your hands are wet. Is this correct?

If the system is grounded via a grounding electrode (rod, pipe, ufer, etc.), the GFCI will trip when/if there is a “ground fault” (potential to ground).

I doesn’t rely on grounding of the receptacle.

Speedy suggested that the Ground is the key element of a GFCI.

If the ground is necessary, how and why does a GFCI receptacle work in the abscence of a ground?

Mark - if you have a “wiggy” or similar device, you can cause a fault at a faucet or other exposed pipe (not that I recommend this to anyone :roll: ).

This is the same condition as if your body was acting as the “pathway” to ground.

Whether the receptacle is grounded or ungrounded, you can rely on the internal test button of the GFCI breaker or receptacle.

Ground being the electrode, not the branch circuit conductor.

I don’t think Speedy was saying that a ground is a key element of the GFCI. For our external GFCI testers to work, however, there must be a ground. This is because the testers that we use, set up a partial short from hot to ground. When this happens, there is more current flowing through the hot wire than on the neutral. This imbalance of current is detected by the GFCI outlet, thus tripping it. So if the outlet is not grounded, our external testers have no way to bleed this current from hot to ground. This is why the external GFCI testers will not test a GFCI outlet that is not grounded.

In a true ground fault situation, current is running through something else, such as a person. This again creates an imbalance in the current, causing the GFCI to trip. It has nothing to do with the outlet being grounded. As Jeff said, the outlet does not have to be grounded in order for a GFCi outlet to trip in a true ground-fault situation.

WoW! Good information!!

Question. If an old house has been upgraded to say a 100 amp service, the kitchen and bath have GFCIs but the rest of the house has not been upgraded as far as new wiring goes, can GFCI outlets work as a grounded outlet without new wiring, utilising the original wire?

I did no such thing.

Thank you Mike Morgan for the concise explanation. You nailed it.
Thank you as well Jeff.

A) The service has nothing to do with the branch circuits.

B) A ground rod at the service DOES NOT provide a safety ground. The neutral to ground bond at the main service does.

C) Are the new GFIs using the old circuits, or were they newly wired?

  1. A GFI installed on an ungrouded circuit does NOT work as a grounded receptacle. It is merely an ungrounded (legal) 3-prong receptacle.

Hey guys

I thought that 6 milliamperes or more would shut off circuit!! Is it 5 mill. State side?