So I was looking into how grounding works and it seems like both the neutral & the ground lines eventually go to ground. The purpose of the ground, to paraphrase, is to complete the circuit if a metal component becomes hot, so it doesn’t get completed when a person touches the metal. Another thing, is that the ground often seems to join the neutral at the fuse box (and seems to in my house).
So my stupid question is, why can’t you join the ground to the neutral line closer to the appliance- say at the socket?
PC
Grounding the green safety ground at an outlet defeats the purpose of the ground fault interrupter system. In order for that system to work properly all of the current that goes out to the system on the energized, “hot”, lead must return via the white circuit ground. If any of the current returns through the green, safety ground it indicates a connections somewhere in an appliance of the the “hot” lead to the structure of the appliance which can be a hazard. When this unusual current condition happens the ground fault interrupter disconnects the power from the affected circuit until the fault in the appliance is removed.
The difference between ground and neutral is that the ground wire carries no current. This insures that it is always at ground potential. Since the neutral carries current, it is not at ground potential, but rather at a slight potential above ground (the infamous V=IR).
Connecting the ground to the neutral at the socket would defeat the whole purpose of running a seperate ground wire.
Actually the ground fault interrupter system allows a small unbalance between the current out on the energized lead and the return current on the white ground lead. I think the unbalance allowed is around 5 milliamperes. To require absolute balance would make the ground fault interrupter too sensitive and it would always be popping out and turning things off.
And, of course, a really good reason is that it is a violation of the electrical code to do this and might have some bearing on whether or not your insurance covers a fire loss resulting from an electrical problem.
While what you say is true not all circuits are required to be protected by GFCI’s.
As a small subtopic, is there a point in grounding to neutral in the socket when there is no separate ground wire (and is it safe to)? That is, when the soocket ground pins are just sitting there with no wire attached to them.
There may be some situations where there is a point or 2 in doing this, but in general not and that pesky electric code gets in the way.
You should not install a 3 prong outlet when you don’t have a ground, or you can use a GFIC outlet as long as you have some indication that it doesn’t have a ground.
True, but I don’t think that’s the primary reason.
I’ll repeat what I said in this thread:
Another good reason is that people make mistakes and sometime will wire the hot to the neutral side. In a moment of carelessness could cause the hot to connect to a chassis ground. Having a seperate wire that is easially identified (ground) connect to a also easially identified terminal is a pretty good way to guard against human error.
True, the code forbids you to make a ground to nuetral bond outside of the main panel.
In the even that you would like to install a grounded outlet where there was none previously due to the lack of grounding conductor in the circuit one may install a GFCI device.
When a GFCI receptacle is installed on a non-grounded system, the GFCI must not be connected to an equipment ground. Also, the receptacle must be labeled “No equipment ground”.
You can now use the outlet as you would a normal grounded receptacle as you are protected from line to nuetral leakage and since no equipment ground exists you need not be concerned about leakage to ground in the typical sense.
Right and this brings in the voltage above earth ground of the white neutral line that is a result of the current in it.
I’m sort of dubious about that one though. According to my wire tables #12 copper wire has a resistance of 1.588 milliOhms/ft. So if a circuit 50 long is carrying the maximum 20 amperes the neutral would be 1.588 volts above the earth ground. Hardly fatal. And if the current goes above that because of a fault in the equipment the breaker should trip off.
Very true. And this is why the argument “the neutral could have a voltage on it because it’s a current-carrying conductor yada yada yada” does not hold water.
A neutral should not be used as a chassis ground, as such a design would be very dangerous should there be a break (open circuit) somewhere in the neutral wire. See my previous post for more info.
Exactly (I think). The green safety ground for non-GFI circuits is a sort of a “belt and suspenders” approach and is a good idea.
This is why I cringe when people tell me they’ve done their own electrical work. Lots of people have no idea what happens in the average circuit much less the safety and danger intricacies involved. “How come I get zapped when I turn my faucet on?” I run the other direction.
I think that outlets/receptacles are designed to make the hot connection first and the nuetral second. Even though the male ends are the same length on the plugs, there must be some difference inside the outlets themselves. Imagine this if there wasn’t; Every time you plugged some delicate electrical instrument into an outlet you may (according to your guess of %50 of the time) make the hot connection first thereby creating an open nuetral circuit temporarily. Or if the plug worked its way loose you may end up with just the hot making the connection and the nuetral open. This would raise havoc on lots of electrical equipment, since we both know that creating an open nuetral on a circuit board or some such delicate device can do some damage.
I’ve looked at a couple of newer outlets I have laying around here and it appears as though the nuetral tabs in the receptacle are closer to the front than the hot tabs.
Uncommon Sense: You’re correct that, for an appliance with a grounded plug (a.k.a. the “third prong”), the ground should be connected first. Notice how the ground prong is longer than the hot and neutral prongs? That’s how it’s done. 
As for the question, “Is it a problem if the hot makes contact before the neutral, or vice versa?”, keep in mind that it is only a safety issue if there is no ground wire and the chassis is connected to the neutral. And because it would be a safety issue, this is never done. My whole point in bringing it up was to explain why a grounded appliance must use a third ground wire.
In our previous home none of the outlets were grounded. To save time and money, I went ahead and replaced each outlet with either a regular, 3-prong receptacle or a GFCI receptacle. By figured out which receptacle was the most “upstream” on each circuit, I was able to GFCI-protect all the outlets by replacing just seven receptacles with GFCI receptacles.
Now while this approach conforms to code in most jurisdictions, it is certainly less than ideal:
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GFCI are prone to failure. Especially after a thunderstorm. And they tend not to be fail-safe.
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Let’s say an appliance with a grounded (3-prong) power cord has an internal short to the chassis. If the appliance is connected to a grounded outlet, the circuit breaker or fuse will blow. If instead the appliance is connected to an ungrounded GFCI outlet, and if the chassis is not already in contact with earth ground, the circuit breaker or fuse will not blow. The appliance will be sitting there dumb-and-happy with a hot chassis, and the GFCI will only break the circuit after the chassis comes in contact with earth ground. And what will make the chassis come in contact with earth ground? Often it is you. So current has to first flow through you and then to earth ground (assuming you’re grounded). Once the GFCI senses a current above 6 mA, the GFCI will break the circuit 50 ms later. I don’t know about you, but this doesn’t sound too safe to me. It’s much better IMO to have a chassis that is always connected to earth ground.
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You can still get electrocuted with a perfectly-functioning GFCI. Just isolate yourself from ground, touch the hot, then touch the neutral. Zapp.
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Some things require an earth ground connection for reasons other than safety:
a. Fluorescent fixtures. Some require the metal reflector to be no more than 0.5” from the bulb and connected to earth ground. The reason has to do with starting… the bulb impedance is quite high during the starting phase, and current is produced via capacitive coupling with the (grounded) reflector. (Or something like that.) If the fixture’s reflector requires an earth ground and you fail to hook it up, starting can be very erratic.
b. Surge protectors. Most surge protectors utilize MOVs, TVSs, and/or GDTs between hot and ground (and sometimes between neutral and ground) to attenuate normal-mode voltage transients. Failure to connect the earth ground will significantly decrease the surge protector’s effectiveness.
c. Shielding. Some equipment utilizes shielding to block EMI radiating into the device and/or emanating out of the device. This includes sensitive radio receivers and amplifiers, switching power supplies, phase-fired controllers, and laboratory instruments. The shield is usually tied to earth ground.
What about equipment safety in a two pronged plug? Wouldn’t you have possible problems if the hot were to make connection first? I know I can make all manner of hell break loose if I open up a nuetral when a computer is plugged into the outlet. Usually the mother board or power supply lets go (if there is no surge protector in use, that is). Even with the longer Ground prong, you may still have the oportunity to make the hot connection before the nuetral, you think this would matter?
Hot breaks, neutral breaks… why would it matter?
Back in the days of metal boxes should the green grounds have been attached to the box?
Also what exactly is a grounded chassis?