Our house was built quite some time ago, so most of our electical sockets are just two-pronged, and not polarized either. But one or two of our electrical sockets have a third “grounding” prong in them. And although it may seem odd, I have wondered for the longest time what this prong is ultimately connected to. I doubt, although I could be wrong, that the electric company has a whole separate line just for grounding. So what exactly is this prong hole ultimately attached to?
This worries me a little bit too, because I don’t want to get accidentally electricuted if it is attached to something otherwise innocuous in my house.
So what is it ultimately attached to? Thank you in advance to all who reply:)
If it’s installed right, it should be attached to everything innocuous in your house. Or, at least, everything metal: Your plumbing, the frame of most of your appliances, etc. And, of course, the ground, which is where it gets its name.
The basic idea is that current flows between things at different voltages, and you don’t want current flowing between the frame of your refrigerator, your kitchen sink, the ground outside, you, etc. So you want all of those things to be at the same potential. The grounding wire ensures that that is the case.
Note the qualifier there, by the way, “if it’s installed right”. If the wiring in your house was done really poorly, it’s possible for things like the handle of your oven to get electrified (rare, but I’ve seen it happen). If you’re worried about this possibility, you can hire an electrician to check it out, and possibly install (properly) grounded outlets in other places, too. If you haven’t noticed anything already, it’s probably not that bad, but there have been a lot of improvements in electrical safety in the past few decades, so it might not be a bad idea to get the whole house upgraded (even if it’s in line with the electrical codes from the time it was built, those codes didn’t include things like GFCIs).
In the US, the ground is supposed to be connected to, well, the ground, either through your buried copper water main or through a “made electrode” composed of ground rods hammered into the ground in a specific arrangement and depth.
For now, I’ll spare you all of the weirdness of the neutral wire, grounded vs grounding conductors, and other electrical arcana. Unless you *really *want to know.
eta: repeat the word enough in one post, and you to can forget how to spell “ground”
My house is old too, and most of the receptacles are 2-pronged. The few with grounding holes don’t have any additional wiring; the receptacles were apparently installed simply to accommodate 3-pronged plugs without an adapter.
Like the name says, it’s connected to the ground – earth – dirt.
Somewhere outside your house there will be a metal rod several feet long pounded into the ground, and a heavy bare wire connected to that, which leads back to the main breaker box in your house, where the ground wires from all 3-prong sockets in your house connect. (Sometimes the metal pipe buried underground bringing the water into your house is substituted for a separate ground rod.)
And the electric company does not have a whole separate line for grounding; this is all done inside your house, in your own wiring. The electric company does have the equipment at their generating plants grounded to the same earth that your house sits on, for the same safety reasons that your house has grounded outlets.
And the electric company wires do have a whole separate ground wire running along their poles, above the power wires, but that’s mainly to protect their power wires from lightning strikes. It’s not connected to the ground wires inside your house (except that it’s also grounded to the same earth as your house).
from your main electrical panel to the wall outlet there are 3 lines. 1 of them is hot and the other 2 are ground and are connect to the same circuit in the panel. The purpose of the 3rd prong is to provide a separate ground for devices that have a grounded case.
A CFI safety outlet looks for any changes between the 2 grounded connections and will turn off the hot line in the event an electrical device has shorted out to the case.
In an old house, the wires may run in metal conduit or flexible metal cable, and often that is sufficient to provide a complete ground back to the main electrical box. Otherwise, it was not proper to install those 3-prong outlets, and they aren’t really safe – they are giving you an illusionary sense of safety.
For both you and the OP, hardware stores sell plug-in circuit testers (like this one) for around $5-$10. You can read from the lights on them if your 3rd-prong ground is good, and various other wiring problems. That’s a worthwhile investment for checking these out.
I used to be an electrician, mostly industrial and commercial, which is why I’m reluctant to give advice.
But, I highly recommend the Black and Decker home wiring book. You may be able to find one in a used book store for a few bucks.
Messing around with house current can get you hurt if you aren’t careful and informed. If you know (learn) what you’re doing it’s as easy as pie.
I admit - I just did this in my house. Our wiring is from the 60s, and all of the outlets in the house are two-pronged (except for in the kitchen, which was remodeled recently). When we painted the living room, we noticed that the outlets had been painted to match the previous color, and so had to be replaced. Well, you can’t buy two-prong outlets any more, at least not at our local Home Despot. So our living room is now populated with three-prong outlets with no grounding. I fully intend to disclose this when we sell the house.
I am not an Elec., But have done much testing on GFCI’s for fire service safety training.
I will object to your analogy.
The GFCI dose not care where the current flows as long as it all eventually comes back through the neutral leg. It is any imbalance in the primary and neutral that causes it to trip. So with the right malfunction one could be fried quite well done and not trip a GFCI.
The receptacle’s “third prong” is connected to a grounding bar in the circuit breaker panel. The neutral prong in the receptacle is also connected to a grounding bar in the circuit breaker panel.
In the panel, all the grounding bars are tied together. The grounding bars are also connected to the transformer’s center tap, and (finally) to a 4-foot rod that is driven into the earth.
The reason I’m mentioning all of this… it is not sufficient to simply connect a receptacle’s third prong to a 4-foot rod that is driven into the earth. The receptacle’s third prong must also be connected to a grounding bar in the circuit breaker panel. If you were to simply connect a receptacle’s third prong to a rod that is driven into the earth (and nothing else), and there is a ground fault, the circuit breaker won’t trip. That’s why the receptacle’s third prong must also be connected to a grounding bar in the circuit breaker panel.
To electrocute yourself through a GFCI-protected outlet, simply don some rubber boots, touch the hot prong with a finger on your left hand, and the neutral prong with a finger on your right hand. You will receive a good jolt (especially if you have sweaty skin) and the GFCI won’t trip.
In most municipalities you can install 3-prong outlets as long as they’re GFCI-protected. This means that the outlet itself must be a GFCI receptacle, or it’s a regular 'ol outlet that is protected by an upstream GFCI, or it’s on a circuit that is protected by a GFCI breaker. The outlet must also have a sticker on it that says “GFCI-protected, no ground,” or something like that.
Hmm, that might be what happened to the house I just bought. The seller did not disclose it, but my home inspector discovered it. The seller was a real DIT type and didn’t pay much attention to codes, but he did seem to know what he was doing.
It became an issue when I connected my computer and the universal power supply detected a fault and wouldn’t work. (At that point we were midway through $3000 worth of electrical work so it got quickly fixed.) The electrical code insists that non-grounded outlets have two prongs, not three, and the electricians replaced half a dozen of these, as that was much cheaper than grounding the whole panel–and I don’t understand why. They did ground certain selected outlets, for the dishwasher, for instance. (This house was built in 1956 and had never had a dishwasher. Hard to believe.)
More generally, the neutral and grounding bars are only connected together at the main panel or service entrance. They are only connected at a single point, and the neutral is kept separate from the ground in subpanels - for example, a shed with a small panel in a residential application, or regular subpanels in commercial/industrial applications.
NEC mandates that the grounding conductor has to follow the same path as the current carrying conductors. This is so that if the ground is cut by a structural failure ( car through back wall of garage, tree falling through roof, etc.) the hot wire probably gets cut too.
In the days of non-grounded outlets, 2 wire romex was common. This means to run a ground conductor back to the panel would mean running new 2+ground romex, which can be a real pain in an existing structure…easiest if there is an attic above the serviced living space, but still to be avoided if possible. The old romex should have been stapled to the studs, so it can’t be used to pull in the new wire, and there should be fire stops in the stud bays, so it isn’t at fun getting a fish tape up to the attic. Dad and I rewired the house I grew up in when I was a teenager…complete with permits and inspections. Learned a lot, I did…most important thing I learned was to find a line of work other than as an electrician.
The house from where I was typing this had some moderizing done to the wiring at some point. It has no attic, and is built on a slab. The new wiring was run in conduit externally and brought through the walls at each outlet. Not elegant, but safe, to code, and it works.
you’re right, I meant to correct my post and forgot. you can get electricuted with a GFCI and it is measuring the difference between the primary and neutral. I was reading up on them after I posted. You could, in theory, put a GFCI on a 2 wire circuit but I don’t know if it’s legal.
Incidental to this, all standard UK sockets are three-prong and have been for ages and ages. (Photo of socket and plugs.) The top prong of the three, at the apex of the triangle, is the ground. (Or earth, as we call it.)
But in recent years I have noticed that an increasing number of appliances come with plugs that are effectively only “2-prong”, as the top prong is made of plastic with no electrical connection at all. The left-hand (black) plug in the photo is an example.
Why is this? I was always taught that proper earthing was A Good Thing, so why does so much electrical stuff these days do away with it?
