Can a GFCI have no ground?

Question

I have an old 20A GFCI in my basement (connected to multiple loads) for outdoor XMAS lights. Today I replaced it with a Leviton 20A GFWT2-KW.

BEFORE replacing:

1. Always tripping, especially during rain/snow
2. no ground wire in the box
3. Receptacle Tester says OPEN GROUND

AFTER replacing:

1. no ground wire in the box
2. Receptacle Tester says CORRECT WIRING

How can this be and how can this be safe?

OLD

New

EDIT: With all the responses about being connected to the panel I have added a higherlevel view of my setup.

Answer 1

Despite the name ground-fault, a GFCI does not actually care about, or use, the ground wire. In fact, GFCI can be added to totally ungrounded circuits in order to provide protection comparable to (in some ways better) that provided by grounding.

With metal conduit and a metal box, you don't need a separate ground wire - the conduit and box are a functional ground.

Since your GFCI/receptacle is installed in a metal box, it should pick up ground via the yoke and a 3-light tester should show a correctly grounded installation.

The previous GFCI may have had too much dirt, paint or (deliberate but stupid) separators between the yoke and the metal box. Or it is possible that, unlike better quality receptacles (which should include all GFCI/receptacles) it simply didn't have the yoke connected to the ground pin.

Your new setup and test results are correct and normal.

As far as:

Always tripping, especially during rain/snow

that is the GFCI doing its job. Rain and snow will cause ground faults on outside receptacles. The solution to that is not to replace the GFCI (though (a) that may have made sense here because of other issues and (b) lots of trips over time are a good reason to replace it to make sure it will work well) but to prevent rain and snow from getting into the circuit:

• Make sure that there are no gaps around the wiring going to the outside receptacles.
• If the outside receptacles are not weather-resistant, replace them with weather-resistant receptacles.
• Add (or replace if cracked/broken) in-use covers to all outside receptacles.

Answer 2

You have a steel box there. Code requires all cables coming into a steel box attach their ground wires to the box, not the receptacle.

You are accustomed to plastic boxes, where running the ground wire to the box would be absolutely pointless and so it must necessarily come to the receptacle.

Note the hard flush metal on metal contact between box and mud ring. So the mud ring is thus grounded. You also see hard flush contact between mud ring and receptacle in your installation. That carries ground to the receptacle.

(though this GFCI can also pick up ground via the mounting screws, since it is identified as "self-grounding" - that's useful when drywall prevents the outlet from landing hard flush on the metal. Also, switches can use the mounting screws even if they are not labeled "self-grounding".)

However, I also see a metal conduit nipple connecting the box to the panel. Metal conduit which is not flexible provides a legit ground path. I use that exclusively, I own 10 colors of THHN wire (for circuit identification) and none of them are green.

Answer 3

Because I haven't seen it mentioned yet: the NEC explicitly allows a GFCI to not have a grouding conductor if it's replacing an old outlet that didn't already have one. It's also required to have a "no equipment ground" sticker, which usually comes in the GFCI box.

NEC 406.4(D)(2)(C)
A non-grounding type receptacle(s) shall be permitted to be replaced with a grounding type receptacle(s) where supplied through a ground-fault circuit interrupter. Grounding-type receptacles supplied through the ground fault circuit interrupter shall be marked "GFCI Protected" and "No Equipment Ground". An equipment grounding conductor shall not be connected between the grounding type receptacles.

(image source)

Answer 4

Addressing two questions here:

1. your comment that the outlet should not reset if it is "wired incorrectly"
2. possible cause for no ground before replacement, that you should investigate

"Wired incorrectly" in that sense means only one thing, that the LINE and LOAD terminals are reversed. You do not appear to be using the load terminals, and if you did incorrectly use them to apply power, it would not reset.

The GFCI outlet does not NEED a ground connection. In fact, one common use of GFCI outlets is to add a margin of safety to a location where there is no ground available such as a very old junction box with a two-pin outlet. But in your location there IS ground available. Some appliances benefit from having it, they use it for noise reduction in electronics notably in audio equipment. Also, appliances with metal housings will be even safer with a GFCI that has a good ground, because if there is a short to the casing inside the appliance it will trip immediately rather than next time someone touches it.

Your old outlet may have shown no ground for many reasons related to itself or the way it was installed. It doesn't matter any more. But there are two things you should check for, that is, that the retaining nuts on the metal nipple connecting the two boxes are both tight, and that the grey paint beneath the nut inside the breaker panel was removed. It's possible the old GFCI did not show ground because that wasn't done properly, and since you now have an indication of that possibility you ought to check for it.

Answer 5

If your box is connected to the panel by metal conduit, then the box is grounded. The receptacle likely is connecting to ground via its mounting to the box.