Does a GFCI need a ground?

No.

Bill

Not all have one, but if it does, it must be connected up. At least in the UK, some use it for the test function. Some include other trip detectors too, such as live/neutral reversal, neutral disconnect, ground disconnect, and will trip in these situations. Some superimpose a tiny neutral/ ground voltage (actually it's common-mode on live and neutral) so they can detect neutral/ground shorts when there's no load current.

So in short, for the pure GFI/RCD function, no ground is needed. If your GFI/RCD has a flying ground wire, then it needs it for one of its ancilliary functions.

Technically no, a GFCI would probably work fine without a ground connected. However, I don't know what code is in your area, but the thought of NOT hooking up a ground scares me.

Aside from that, the "test" button on most GFCIs wouldn't function, which alone makes it a BAD idea (otherwise how would you be able to tell if the GFCI is still working?)

Not true

The listing spec for GFCIs says it must function without a ground. The test button introduces a 8-10ma signal across the current transfiormer to trip it. A hand held GFCI tester won't work without a ground.

The GFCIs with which I am familiar, work even if they are not grounded, but it is safer if they are grounded.

If the appliance and the GFCI are ungrounded, then all of the ground fault current goes through your body until the GFCI can disconnect the power. If the GFCI is working properly, then probably you will live through it, but depending on the amount and duration of the fault current, and on the path that it takes through your body, there may be significant damage.

If the appliance and the GCCI are grounded properly, then at least most of the ground fault current goes directly to ground, and thus bypasses your body. And if a significant ground fault occurs while the appliance is energized but while you are not touching it, then the GFCI disconnects the power before you touch it, and no ground fault current goes through your body.

GFCIs are great safety devices. But trusting your life to a GFCI, is like playing Russian roulette with the gun safety on; if a ground fault occurs, and the GFCI malfunctions, then you die.

Dick Alvarez alvarez at alumni dot caltech dot edu

As stated above, a GFCI with a real safety ground is a lot better than a GFCI without one.

In the US, ungrounded GFCI's are permitted where a real ground is unavailable (as in old work). You are supposed to mark them as "ungrounded" or "no ground". Most come with little stickers for this purpose.

Beachcomber

Beachcomber

I have a GFCI receptacle dissassembled on my bench right now, that has hole for the ground prong and absolutely NO metal in the hole. The green ground screw connects to the yoke, and only the yoke. It is brand new, UL listed unit. So - with this GFCI, and possibly others, there is NO ground connection to the equipment plugged in to the GFCI. The point to emphasise is that with a grounded GFCI, you might not be any safer than if it was not grounded. With this one, which came from Harbor Freight, item #43756, you are not.

Ed

I just discovered my mistake. The *yoke* has contacts on it that, when assembled, go into the ground hole on the GFCI so that the ground prong from the equipment plug will be grounded. With it disassembled there's no metal in the hole. Duh.

Ed

I have heard the GFCIs at Harbor Fright had a counterfeit U/L listing. They may have fixed that by now.

| A ground fault circuit interupter senses the difference between hot and | neutral, and trips when they are not equal. | | Does it really need a ground contact?

If you are hooking up a new circuit, put in the ground no matter what the GFCI needs. If you have an existing circuit without a ground, most (if not all) GFCI devices will function just fine.

A GFCI serves to detect leakage current (an imbalance between the current carrying conductors, indicating that some other path is part of the circuit that should not be). The safety feature is to shut off the power when such leakage is detected, which may be going through people. The safety of having a ground is (among other things) a means to ensure metallic components of load equipment do not have any voltage potential from current carrying conductors, and provide a low impedance path to allow over current fault detection to activate properly if there is a short. Neither requires the other. Having both maximizes safety.

Modern, up-to-date GFCI's on the North American Power Systems detect (and will trip OFF) on two conditions.

1. Imbalance in HOT vs. NEUTRAL Current of 5 ma. or greater.
2. A short between NEUTRAL and GROUND (on the output side or downstream from the GFCI).

As stated in previous postings, installation of new work requires the

3 prong outlet and a safety ground condutor. (In some cases, this can be the conduit itself, if the other wires run in the conduit and the conduit is grounded).

Old work (knob & tube and the ungrounded systems installed before the late 1950's and early 60's) where the outlets just had a hot & and neutral wire with NO ground wire.... These are the only places where a GFCI is permitted to be installed with no ground. The GFCI outlet should be marked "NO GROUND" to comply with the code requirements.

Beachcomber

Ed The UL label is undoubtedly counterfeit. UL would not list a receptacle that will except a grounding plug without providing a conductive path from the grounding pin of the plug to the grounding terminal of the receptacle. Coming from Harbor Freight that is no surprise.

-- Tom Horne

"This alternating current stuff is just a fad. It is much too dangerous for general use." Thomas Alva Edison

It was my mistake - look at my correction dated 8/25. Ed

Technically speaking, I don't understand why a GFCI Receptacle would need a ground connection...

If it measures what goes out (black), and compares it to what returns (white), why would it need the ground conductor? The ground is, according to my understanding, to provide a low Z path for fault current rather than through the CBLF holding the malfunctioning apparatus. But if the fool thing trips off at 15 mA, whatever for the ground? In case the GFCI malfunctions? (So test the thing. Like the mfr. recommends...)

If I am missing something elementary, please clarify.

H.

Yes the bit you may be missing is- The grounding connection needs to be there thru the plug in GFCI so that a device with grounding will be connected to ground as required. Simply in itself the GFCI does not require a ground to its job but it must pass a ground thru to any connected device.

Maybe, except for say a double insulated hand tool, for instance, with a two-prong plug. These do not require a ground, so then the GFCI would not require a ground in your example, right?

In fact, except for extension cords not much requires a ground anymore. I have an electric lawn mower and it doesn't even have a ground prong on the plug. Hair dryers; shavers; none of this stuff needs a ground connection anymore. (Even the stuff that James Bond might throw into a bathtub with an enemy agent doesn't have a ground plug any more...)

And since the ground conductor is sort of superflorous when plugged into a GFCI, why do you need to maintain the ground connection, anyway?

H.

Because Until ABSOUTLY every appliance that is ever likely to be pluged into an outlet has only a 2 pin plug, then every outlet must provide the ground, that is pass it thru from the outlet to anyting plugged into the GFCI.

The ground hole in a GFCI receptacle has nothing to do with GFCI operation. Code these days requires that any receptacle, including GFCI receptacles, installed on new circuits have the ground hole and be capable of providing ground to a 3 prong plug.

Ed

| Technically speaking, I don't understand why a GFCI Receptacle would | need a ground connection...

It does not need a ground to perform the "ground fault" detection function. That is performed simply by comparing current balance in the conductors intended to carry current. What is out of balance must be leaking somewhere and that is generally to some sort of ground, which is not necessary the grounding wire (it wouldn't be that wire if that wire is not present).

| If it measures what goes out (black), and compares it to what returns | (white), why would it need the ground conductor? The ground is, | according to my understanding, to provide a low Z path for fault current | rather than through the CBLF holding the malfunctioning apparatus. But | if the fool thing trips off at 15 mA, whatever for the ground? In case | the GFCI malfunctions? (So test the thing. Like the mfr. recommends...) | | If I am missing something elementary, please clarify.

The grounding wire needs to be there simply because it is required by the electrical codes for the safety function it serves, which is different from what a ground fault detector does. They are separate functions, but both complement each other by adding safety.

Grounding is required virtually everywhere.

Ground fault detection is required in places where a greater risk exists to create a ground fault, or where there is an increased hazard due to a ground fault.

If you have an existing circuit with no ground, either installed before the code required grounding, or installed in violation of the code, you can modify that circuit to add ground fault detection either at the circuit source (e.g. a GFCI breaker) or near the load point (e.g. a GFCI receptacle) and the ground fault detection functionality will work. The test function will also work if wired correctly (some may have been wired to do the test by leaking some current to the grounding wire, which would make their test fail if the grounding wire is absent).