Question for those who know about electricity

To be precise, the ground/common bar in your breaker box isn't just connected to ground. If you look carefully you'll see a connection going back to the power company as well. The connection back to the power company takes most of the common load away.

__________________
Ask Me About Linux System Administration

Exactly my point... it makes no difference if the current is directed back to the ground via the white wire... or the bare wire.... its going to trip the breaker or blow a fuse...

And like the bird who sits directly on the high voltage line...quite safely I might add, unless you get between the hot and the ground, yer prolly not going to get zapped.

__________________
"Nothing so needs reforming as other peoples habits." Mark Twain

Yep I am aware of this too. All the more reason to question the need for that extra bare wire.

__________________
"Nothing so needs reforming as other peoples habits." Mark Twain

I used to ponder that myself, but as it turns out there is no active current flow to speak of backing up to the ground connections.

So do you have a 2-wire problem you are trying to solve? I've got that problem in my house too.

__________________
Ask Me About Linux System Administration

nope, I dont have any wiring problems, its just a nagging question thats been bugging me for a lotta years... and have yet to have even the guys with the power company give me a good answer to it... after they stop and think for a bit. They always come off with the code book, and "for your safety" until I query them further and make them think about the circuitry involved and WHY... they get puzzled looks after a while and tell me right out... I dunno... thats just what I was taught. I always sorta thought it was one of those things that the copper industry "sold" in order to sell 50 percent MORE wire to the construction industry.

As to the "no active current backing up", of course not.. there is nothing at the other end of the bare wire to complete a circuit... just like there is nothing at the washing machine housing to complete a circuit.

__________________
"Nothing so needs reforming as other peoples habits." Mark Twain

Thanks folks, that advanced my education some.

Glad we could be of help.

__________________
"Nothing so needs reforming as other peoples habits." Mark Twain

Oh fer Pete sake.

My dad was an EE who built radio stations. I helped with a bunch of stuff, like building studios, etc.

The white and bare ground both go to the buss in the entrance box, and that is bonded to a ground rod as well as the common (center) tap of the pig on the pole. Those are the only two points you need to be worried about. Any ground to a power station has little or nothing to do with you and more about the distribution system and protection of it from lightning. Transmission lines are three phase (three current carrying wires).

Anyway, the moment you run a current through an appliance, that current is passing between the white wire and black wire. If it was only in the black wire, you wouldn't have a current, wouldja?

So... when that white wire is carrying current it is ABOVE ground. It has a voltage and amperage in it. It is, for the purpose of the discussion, HOT. Not as hot as the black wire, but HOT just the same. Even though the ground wire goes to the exact same spot, it is NOT carrying any current at all. You can touch it with one hand and a grounded pipe with the other and not get a shock. If you try the same stunt with the white wire while it is energized, you WILL have voltage going through your body. It may not be a lot, but it doesn't take a lot to kill a person.

If there is a minor ground fault, then yes, a minor amount of current will be going through the ground wire and it too will be "above" ground potential. So... ever wonder why outlets are starting to be GFI (ground fault interrupter) protected?

The code has evolved over the years as more has been learned about the dangers of electricity and people have become more stupid.

__________________
George Washington did not run and hide.

Ok, so what you are saying is the bare ground wire carries no voltage or amps, while the white neutral wire does carry a minor amount.... so explain why the ground wire is needed again? If I understand it right, it will carry voltage if something goes wrong with the appliance??? is this correct? If so, why not just ground the appliance to the neutral wire and let it carry this voltage along with the minor amount its carrying?

__________________
"Nothing so needs reforming as other peoples habits." Mark Twain

Because if there was an electrical fault that created an open circuit in the white wire, you could have a potentially dangerous voltage present on the device. The ground wire bleeds off that voltage, and hopefully passes enough current flow to trip the circuit breaker (or blow a fuse) to de-energize the circuit.

__________________
Only the paranoid survive.

I carry a gun because a cop is too heavy.

Dispatches From The Conservative Underground

Ok, this almost makes sense. Except....
A. if the ground wire is completing the circuit instead of the neutral..(which it should never do if wired correctly) there will be no more current flow than is normally there, thus not tripping the breaker and rendering it any safer.
B. if the bare ground wire is connected to the housing, and managing to pull enough current to operate the device... it is directing the potentially dangerous current to the housing device itself at all times... which appears to be more dangerous than simply chancing a short in the device at the same time there was a failure in the neutral wire.

a ground fault breaker on the other hand would trip the breaker killing the power supply to the device.

__________________
"Nothing so needs reforming as other peoples habits." Mark Twain

Look at your power tools. In particular, look at a double insulated drill. This is a drill with a plastic case and only two prongs on its plug. It doesn't use the ground lug. That's because with the plastic case, if the hot wire break off inside the drill and touches the case it cannot make the drills body electrically hot. Ie, you can't get shocked by the wire breaking inside.

Now look at a metal drill, with a three pronged plug. If that drill breaks the hot wire inside it can make the metal case electrically hot. But, with the case of the drill being grounded through the third leg, you won't get shocked (probably). The electricity is far more likely to go down through the bare ground and out. And, it will likely trip the breaker because of the short.

Neither system protect you from dropping the electric drill into a bathtub, or working in the pouring rain.

The ground isn't there for your house or shop wiring safety, it's for the appliance.

It would depend on where in the circuit the fault was located as to how much current it would send through the ground wire, but since the ground wire is at zero volts, more current would flow anyway, and hopefully that would be enough to cause it to trip. A ground fault breaker wouldn't work unless that ground wire was connected.

__________________
Only the paranoid survive.

I carry a gun because a cop is too heavy.

Dispatches From The Conservative Underground

You might be interested in reading this site.. It talks about stray voltage and the reason a properly installed ground-3rd wire is so important.


http://www.bassengineering.com/SV_Cause.htm

When you consider that so many of the power lines are original or only barely updated from the very first installation by REA I think it is a very worrisome though.
Some of these old houses have original wiring. But they also have modern appliances which the house was not wired for.
If the power company has not updated their lines from the 30's, 40's, 50's etc you think how homes have changed since that time!

I was having problems at this place and seeing that the transformer was old and rusty, ie. leaking!! I demanded a new transformer. Honestly a leaking poison transformer that was the first and original one in this area meaning it was at least 60 years old!

I know by adding an extra ground wire my phones lasted longer.

Thanks for the link. some interesting reading there and it brought me up to speed on some of the stray volatage issues that I had not heard before... however it still did not answer my basic question.. and as a matter of fact mentions some things that re affirm my suspicions about the need for the third wire.

__________________
"Nothing so needs reforming as other peoples habits." Mark Twain

Basically it is a redundant wire to increase safety by supplying a source for current to travel, pure and simple, things will run without it but it is there as an extra precaution when a short occurs.

Dont worry YH your not the only one who had wondered this. My house was built in 1938and had an old 60 amp and a second 40 amp breaker box with cloth wiring and all two pronged outlets when we bought it. We also had NO grounding rod and the triplex was physically laying on the roof and then attached to the house through ceramic insulators.

We put on a new weather head on a mast, replaced the two breaker boxes with a new 200 amp box and I have slowly rewired most of the house but I still have some two pronged outlets where we only have lamps plugged in and some light fixtures in the basement that do not have the bare ground.

If you look how everything is set up, it does seem to be that the neutral and bare ground would do the same thing in event of a fault and I have seen many times in newer houses where the bare ground is there but not hooked up particularly on overhead lighting fixtures. I am slowly getting everything replaced and using the bare ground but I dont think YH's question is just for the sake of argument and I bet a lot of us have wondered the same thing but didnt have the stones to really question it.

__________________
www.salmonslayer-simplelife.blogspot.com

That old wiring with the rotting cloth insulation scares me lot more than no ground wire when I'm working in older buildings. If it was mine it would be replaced, or at least disconnected.

And I've had couple old metal casing power tools WITH 3pt plug used in a house with ground circuit and still got a shock. Shock me once, shame on you, shock me twice shame on me for not throwing the blasted thing away.

__________________
"What would you do with a brain if you had one?" -Dorothy

"Well, then ignore what I have to say and go with what works for you." -Eliot Coleman

its a redundant path to ground if the neutral return fails. it has other functions like chassie grounding./

Great link, Waiting Falcon. Totally on target.

Ground or drains make more sense when you understand that everything has electric potential. A ground rod is not at 0% electricity, it simply is reflective of the most common potential in the area. A passing thundercloud can raise or lower that potential.

The key is you want 0 DIFFERENCE in potential at various local points and with appliances. With electricity, you are not limited to having just current flow, an appliance can have at least three other factors creating an electric issue.
Capacitance - a wire or plate at a voltage can create a potential by acting as part of a capacitor, with the case being the other part.
Inductance - a wire, transformer, motor, whatever can create and induced current to the case by creating magnetic lines of force which are then broken.
Static buildup - which can in part be caused by the above. Something with the potential for a lethal static buildup is the area around the flyback coil in a CRT television. For technical reasons, grounding the case through the white wire is a horrible idea. That means either double insulating and using torx screws to keep people from opening things up, or a ground, or a combination.

The ground wire in effect "drains" these potentials to the ground rod. Drain is not exactly accurate, so the term is obsolete.

The other effect, which I alluded to earlier, relates to how current flows. Say you are using an 100' extension cord and have a big saw plugged in at the end of it. The extension cord has a resistance of its own, X number of ohms per foot of wire. If you were to tap into the white wire at various points on the cord while the saw was running, and run a meter between the tapped point and ground, you would find varying voltages all along the path, going between ground and the tapped section of wire.

Now take that two wire extension cord, run it in your house to connect a few sockets to your main breaker, just like house wiring is done. Your first socket might be close to the panel in your bathroom. The second might be 12 feet away in your living room, the third has a socket for your big saw. Household wiring commonly connects a few outlets or lights into a single circuit.

Someone turns the switch to the saw on. You are in the bathroom, using an electric razor, which uses white as a ground in the bathroom, while putting your hand on the wet sink faucet. You create a circuit between the white wire and the sink and fall over dead. With a third wire dedicated as ground, you finish shaving, not realizing what a close shave you have had.