While trying to troubleshoot why some kitchen electrical outlets in this junction box weren't working, I did a bit of research. Apparently, there is supposed to be a ground connection (other than the screw going through the frame of the outlet to the box) from the GFCI outlet to the junction box. (see photo:
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) Can I just run some wire from the green screw terminal on the GFCI outlet to the box? Where would I attach it to the box? By the way, the problem with the outlet was that the breaker tripped in the GFCI. There are three pairs of wires in the photo. One is the incoming AC. One feeds another GFCI outlet down the line. The last pair goes to a switch in the same junction box which turns on some lights in the kitchen.
Having a ground-wire connection to the GFCI itself is a good idea, if a good ground is available. It's not (I believe) strictly required - a GFCI can be used on a two-wire circuit.
In your case, it does appear that the outlet box is probably grounded; I see what appear to be bare ground wires entering at the back. These wires *should* be securely bonded to the junction box - this would probably be done right at the back, where the screws and wire clamps are located. I can't tell if those ground wires are in fact securely bonded to the box, or whether they're just sitting there.
If you're going to ground the GFCI, you'd run a wire from the green screw terminal, to a connection point with one of those ground wires... e.g. if the existing bare ground wire is screwed to the box at some point, you'd want to connect the ground wire to that screw or to another box-mounted screw not too far from it.
Now, the lack of a ground wire from the GFCI shouldn't tend to cause the GFCI to "trip" mistakenly. A proper GFCI operates by measuring "current imbalance" between the hot and neutral wires. If more flows through one than through the other, then it's almost certain that some current is flowing to ground (somewhere) rather than back through neutral... and this is a Bad Thing (shock hazard, or shock occurring).
A GFCI's protection does *not* depend on measuring current flowing through its own ground wire. That's why they can be used to protect two-wire circuits, where there isn't even a good ground connection available... this makes them useful for retrofitting older house circuits for improved safety.
Having a good ground on a GFCI circuit is actually likely to make the GFCI trip sooner, rather than later, if an electrical fault exists. For example, if you have an appliance with a grounded case, and a leak or short develops between "hot" and the case, the GFCI will trip instantly. If the case isn't grounded through the third prong (e.g. if there is no ground prong, or if it's cut off or defeated with a "cheater", or if it's plugged into a 3-wire outlet with no actual ground) then the fault won't result in current flow to ground... until somebody touches the case and also touches something grounded. At that point they'll get a shock, and (knock on wood) the GFCI will trip fast enough to protect them from anything more than a scare.
So, if your GFCI is tripping, then I don't expect that grounding the GFCI more securely is likely to change this. You may actually have a current-leak-to-ground on one of the circuits you are protecting. Or, possibly, interference from a strong local radio transmitter is "falsing" the GFCI - it does happen.
I should have been clearer in my description. After noticing that the power was off to the outlet, I pushed the GFCI reset button but I didn't hear a click. At that point I figured either the GFCI hadn't tripped and there was an internal problem, or it had tripped and there was something wrong with the resetting mechanism. I removed the outlet from the wall and that's when I noticed the missing ground connection. Regarding the GFCI, there was nothing wrong with it. I read on a message board that you may have to apply quite a bit of force to get it to reset. I tried again and it finally reset. This was the first time this GFCI has tripped.
I looked again at the ground wiring you see in the picture. It exits the box through a hole in the top of the box. If it's secured to anything outside the box I can't tell. Is there some official test to perform to check if a junction box is grounded?
Those things work with or without a ground. It could be nuisance tripping, it happens with anything. If that is the case it is defective. To be sure d isconnect the load side and see if it still trips.
If it does and there is nothing plugged into it, it is bad, if it does not trip, it is something off the line coming out of it that it is supposed to protect, and actually is probably doing its job.
The way to find out all what runs off it is to disconnect the OUTPUT neutra l and with the branch circuit turned off, go to every neutrl around. I have wired them to protect lights, you have to for the over the sink lights. In some places you can't even do that, you have to install a GFCI breaker and run all new to the kitchen or sometimes bath. The NEC does ot necessarily require it, but some rehab codes do.
If it continues to work it was a nuisance trip. they are quite sensitive. A little spray of water into anything runniong off it can trip it. In fact c ertain funny loading appliances can make it trip due to certain harmonics o n the power line, depending on how they are designed, even if they are not plugged into it sometimes.
OK, understood. Yes, those trip/reset arrangements can be "stiff". I think they may put a lot of tension on the springs inside, to make sure that the disconnect opens reliably and quickly.
It's fairly common for romex cable (heavy, flexible in-wall wiring) to have two insulated connectors (hot/black and neutral/white), and one bare ground wire between them. That's what you may be dealing with there.
Yes, it can be done, but it's a bit tricky.
The simplest sort of tester is a small plug-like device you connect to the outlet, which has several LEDs or neon bulbs inside. What you would want to see, usually, is a couple of lights lit (indicating that a voltage differential exists between line/neutral and line/ground), and one or more other lights not lit (e.g. the "hot and neutral are reversed" light). This will catch a couple of common wiring faults (no ground at all, and ground/neutral reversal).
These simple testers are cheap, some even come with a "deliberately trip the GFCI by leaking a bit of current" button, and they're a good thing to have in your home-repairs drawer.
Gardner Bender GFI-3501 is one such (currently $8 at Home Depot); there are many other brands.
These won't necessarily tell you that you have a *good* ground on the circuit, though, because this sort of tester is designed to draw almost no current at all through the circuit. It may tell you that ground is connected, when its only connection to the actual building ground is through corroded conduit and when the "ground" won't actually carry much current reliably during a fault.
And, it won't catch the case in which ground and neutral have simply been connected together at the outlet (i.e. no "real" ground). This is a code violation and can be a safety issue.
Doing a *good* test for these faults usually requires measuring voltages between the three terminals, while also pulling a substantial current load on the circuit. Other tests would require powering down the circuit (e.g. at the main breaker) and measuring resistances. It's probably best to have a professional electrician perform these sorts of tests, if you have doubts about the circuit.
A GFCI outlet should trip if there is a voltage difference between the grou nd wire and neutral. Any flow there indicates a potential problem and shou ld cause it to trip off. Without a ground connected, this effectively prev ents the GFCI from working properly. The holes at the rear of the box are for ground screws. You should connect the ground to there. Also, it looks like the ground wire is "grounded" to the box by being folded back into th e entry hole with contact at that point. This installation was not likely done by an electrician. Proper grounding is necessary for proper functioni ng of the GFCI outlet.
Wrong. An imbalance between line and neutral is supposed to trip it. The imbalance is current going to the ground conductor, or another path t ground that causes the imbalance. GFCI are supplied with labels for two prong, ungrounded outlets. Since most of what is plugged into a protected circuit is two wire, they would be useless if they are like you describe.
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I believe that your description of how a GFCI works, is incorrect.
Everything I have read about them, says that they trip when they sense a *current* imbalance, between "hot" and "neutral". They do not sense voltage differences between ground and neutral. They can operate without any ground connection at all.
Basically, they run these two wires through an inductive transformer core in a "balanced" arrangement, and have a secondary sense wire in the same core. If the current flow in hot and neutral is the same, the fields around the two conductors are equal but opposite in phase, they cancel out, and no current is induced in the sense wire. If there's any hot-to-ground current flow "downstream" of the sensing transformer, then the current flow in the neutral wire is reduced, the two currents don't cancel out entirely, a current is induced into the sense wire, and the GFCI detects this current and trips.
Citation:
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from the U.S. Consumer Products Safety Commission. This fact sheet describes the current sensing design, and specifically points out that a GFCI can be used to protect a two-wire circuit which has no ground connection at all. All of the other references I have seen, agree with what the CPSC is saying here.
[An episode of "CSI", years ago, got this wrong... the lead story was a murder which was arranged by tampering with a drill that was plugged into a GFCI - cutting off the ground prong on the plug and then arranging for a current leak. In fact, a GFCI would have tripped under these circumstances, even with an un-grounded tool case and even if the ground connection on the GFCI itself had been cut.]
There are usually threaded holes in the back of metal outlet boxes for ground wire attachment.
See those 2 holes in the center of the box near the sides? They should be for grounding the box. Try an 8-32 screw. Also it doesn't appear that the ground wire is *firmly* bonded to the box. It looks like it's just sort of pushed in with the romex under the clamp.
The ground wire is connected to the ground screw of the duplex, your outlet in most cases, if not, it's connected to the metal box and when the duplex is screwed into the box, it then gets connected to ground. You can also have it both ways which is better but takes longer to install.
Ground wires are part of the romix wire so it gets connected to your main ground in your home back at the sub panel box, where your breakers live. In there the ground wire is attached to the same bus strip as the neutral wire.. Somewhere around there you should have a real earth ground connecting to the sub panel.
Although a GFCI will trip with an older non grounded system, it's not advisable, because in order for this to happen, the circuit has to become unbalanced and if it is the appliance that is shorting, you maybe touching it at the time. Grounds are there to isolate you from the high potential when things go wrong. Having no ground plug means the appliance is not grounded.
As for the reset on the GFCI outlet, for most units your power has to be on before it'll reset.
I have found this not to be true. However, to test, it does require power.
Also, I stand corrected her or in the othe rgroup, that the ground is not even reqquired for the test button to work, originally I thought it was.
All of them I ever installed were properly grounded so whatever. I thought it took current to the ground for test. It does not, it simpley takes it to BEFORE the GF circuit and that causes the imbalance that makes it trip and prove itsel
The test button does nothing without a connection to ground. It causes an imbalace between line and neutral by diverting a few mA to ground form neutral.
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Anyone wanting to run for any political office in the US should have to
have a DD214, and a honorable discharge.
GFCI are allowed on non grounded outlets. If the device is 'shorted' it will trip a circuit breaker. If it has developed a fault path to the case, you won't trip it unless you are touching the defective device and a suitably grounded item.
--
Anyone wanting to run for any political office in the US should have to
have a DD214, and a honorable discharge.
The test button does not require a ground. The hot and neutral go through a current transformer. The test button connects a resistor to the hot ahead of the CT and the neutral downstream from the CT (or vice-versa). Plug-in GFCI testes do not work without a ground.
I agree with everything else you have written here.
------------------------------ Interesting feature - There is a second CT that tries to create a common-mode current on the hot and neutral. If there is a plugged-in or downstream N-G connection the GFCI trips.
sort of. My tester is a 200 watt bulb, but larger would be better. Connect one lead to hot and the other to the box of your ground. With the load on, measure the voltage across the bulb. If it's not the same as the bulb connected to hot and neutral, you have a faulty ground. The connectivity and resistance should be as good as your neutral itself.
A plain volt meter test from hot to ground is not valid, and neither are those little pocket testers. They don't run a real current through ground, which is something that has to happen if your equipment faults. For old installations like in that photo, you have no idea what's really going on or how many times it's been messed with in the past, and how secure the connections are now.
I was thinking exactly the same thing! Without a decent amount of current going through the ground circuit, how can you tell if the ground connection is really firmly attached? I was thinking of using a coffee maker as the load. I'm going to the hardware store to get the appropriate sized ground wire, attach it to the box, then measure the voltage difference with the pot running off hot and ground, then hot and neutral.
Not necessarily. There is some voltage on neutrals in some places. This is caused by heavy loading on one side of the 240 compared to the other. It can be worse if common neutrals are used.
Saw one place that had like 20 volts on the neutral because of two 110 volt window AC units that happened to be on one side of the line.
Good point- there could be other serious problems with such a test.
But still, if you're in the US, have 20 volts on neutral relative to ground, you probably have a bad neutral, which is also a big deal. This problem could even exist outside your home, over at the distribution transformer or wiring from there to your meter.
If your neutral "drifts" by 20 volts from ground, where it should be bonded at the service entrance, and you have split phase 240 (120+120) service you've got half the house with 100 volts at the oulets and other side with 140 volts. That's not good for any devices or appliances you have.
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