Home Wiring Question About Ground Fault Interrupters And Ground

[Ornery]

I know my way around wiring homes and electronics in general, but am still mystified by "safe" grounding. My home has a mixture of "knob & tube" wiring and 3 conductor "Romex". My fuse box is using screw in fuses that have breakers built into them. They're 15amp devices because of the 14 gage wire used in the old wiring in most of the house. The circuits are as safe as can be using this old wire. All outlets are wired with neutral and hot wires on proper terminals.

What I would like to do is add GFIs to some of these circuits. There are no grounds coming to the outlets. An electrician at work said it would be possible to wire the GFI without a ground. Another said it wouldn't work. I have a feeling I can get the outlet to work with the GFI, but will it be as safe as one with a ground?

Can somebody explain to me how the ground makes the circuit safer? Since the neutral wire connects to the ground bus in the breaker box anyway, what is the point of it? I've jumpered the neutral to the ground on an outlet or two just for the heck of it. A simple tester shows those outlets to be "properly" configured with no open ground or reversed polarity. One friend brought over a high tech ground tester to check out my hack job. It said in the instructions that if the outlet was within 3 feet of the breaker box, it would not give accurate results. Hmmmm, so does that mean if I jumper the neutral to ground with a 6 foot piece of wire, it will then be "proper"? It will test as such with that fancy unit!

More food for thought: Our hair dryer comes with a GFI connected to it. It only has two prongs, a neutral and hot. So, how does that do it's job without a ground? I've been struggling with this question/subject for years, asking anybody that might have a clue, and still have not figured it out satisfactorily!

 

[chess9]

Ornery:

I believe the difference is the time difference. A GFI works in milliseconds when the ground is adjacent. If the ground is 50 feet away, you've increased the time to trip the GFI and increased the danger. I would try to run a ground to a nearby pipe, if you have a metal one. Also, GFIs should be on their own circuit as I recall.

I just went through a troublesome GFI problem and THINK this is accurate advice. Certainly it is worth what you've paid for it.

Edit: Your hair dryer GFI sounds bogus to me. I wouldn't trust it.

 

[etech]

I'll try to answer a few of the questions.

The ground makes the circuit safer because it normally does not carry any current. The neutral is the return path to ground so it carries the same current that the hot wire carries. If there is a resistance in the neutal wire it then has a voltage on it and is dangerous.

It is not recomened to tie the ground to neutral because it defeats the safety aspect of the seperate ground wire.


The 6 foot piece of wire would not be safer. I assume that it has to do with the way the tester tells if a seperate ground wire is installed. It needs a minimum resistance to work( ie. more then 3 feet of wire resistance).

Grounding to pipes does not meet code where I live due to the lack of a satifactory ground and the prevelence of plastic water pipes nowadays.

leviton
Note: In accordance with NEC Article 210-7(d), a GFCI receptacle may be used to replace an existing non-grounding 2-wire receptacle. In addition, existing non-grounding 2-wire receptacles may be replaced with grounding-type receptacles when they are supplied through a GFCI receptacle. (In this case, however, a grounding conductor should not be connected between the GFCI receptacle and those receptacles that it
supplies).

NEC Code see 210-7.....

 

[cxim]

There are a couple of different things you can do.

put a GFI in each circuit, for protected circuits, near the breaker box. Probably the best to do if you are really looking for safety.

Run grounds to the outlets. Usually not practical.

The GFI circuits measure input & output & shut off if there is a significant difference. To make this measurement accurate, one must have a valid ground for reference that is seperate from neutral.

 

[jobert]

I've always been amazed that back at the fuse box
the neutral (usually white) wire and the separate ground
wire (usually bare copper) end up being tied TOGETHER.
I have always been told that the purpose of the separate
ground wire was for added safety... it is connected directly
to all metal parts of electrical appliances,wall switches, etc.
so that if any metal part gets hot accidentally the electrical
charge will go to ground immediately (and blow the fuse
if its a sizeable current), instead of traveling to ground
through the body of someone touching the appliance or switch.
Since they're tied together, I would imagine a GFI could function
correctly using the neutral wire.

 

[jobert]

Here's some more info:

Can I use a GFCI in a 2 wire (ungrounded) circuit?
Yes. A GFCI monitors for a current imbalance between the hot and the neutral conductors therefore a ground connection is not necessary. This is allowed per article 210-7 of the National Electric Code.

Do receptacles break only the hot wire when they trip?
No, all of our GFCI products break both line and neutral when tripped.

All of these devices operate on the same principle.
The live and neutral wires are passed through a magnetic core. Under normal conditions, because the current in both conductors is equal and opposite, there is no flux in the core.

Under certain fault conditions, the current in the live wire can exceed the current in the neutral wire. This produces flux in the core.

In the GFCI, the core has a secondary winding. When there is flux in the core, the secondary winding produces a voltage. The voltage is applied to a solid-state amplifier whose output is applied to a relay coil. The relay interrupts the line and neutral conductors.

Typical GFCI is built into a 120-volt duplex outlet. It trips at 5 mA.

Other GFCIs are built into 15-amp circuit breakers. These trip at 20 mA to account for the leakage of the wiring between the panel board and the devices being protected.

In the USA, many professionals believe that the GFCI detects current in the ground wire. GFCI manufacturers support this myth by requiring the GFCI be only installed where a ground wire can be connected.

Because the GFCI/ELCB/RCCB operates on differential current, a ground wire is not essential to its operation. A GFCI operates equally well without a ground wire connected to it. I've done it! (This is not a recommendation or advice to install a GFCI contrary to manufacturers instructions; rather, I simply want to make the point that GFCIs operate on differential current, not on ground wire current.)

Richard Nute
San Diego

Source: http://www.hut.fi/Misc/Electronics/docs/safety/gfci.html

(I hope this guy knows what he's talking about).

 

[chess9]

Geez, I didn't know you didn't need a ground. Very interesting. Neat topic too. I'll have to save this puppy.

 

[etech]

Chess9, as an interesting exercise compute the time differnce in tripping when a GFCI is 50 ft. away compared to installed in the wall outlet.

Hint, electrons travel really fast.

 

[Ornery]

I should have known you guys wouldn't let me down! The only reason I posted this is because I'm in the middle of a pretty big remodeling project and will be picking up some of these GFIs on my next trip to the building supply store. Damn, they're only about $6.00 each in whatever color you want! I remember when they first came out, the price was closer to $40.00!

So, it appears I have good reason to be confused. From what I see in your posts, and read in the links, I might just have it figured out. The chassis of a device is tied to ground. The neutral and hot are kept away from the chassis. If voltage/current did get applied to the chassis (and the user subjected to a shock) the ground would carry the voltage/current back to the breaker box and trip it. If the neutral were shorted to the chassis, it would not trip. A GFI trips faster than a breaker, so the user would never experience a shock. Matter of fact, if a device is properly grounded, the user should never receive a shock either way. If the neutral is jumpered to ground, the device theoretically would be just as safe as if it had a ground wire running all the way back to the breaker box. It might not be "to code", but I feel pretty certain it would be safe.

I'm going to hook those GFIs up all over the place. At $6.00 each I can afford to do the whole house easily! A "Hot Deal" for sure!

 

[chess9]

Etech:

Well, for the first time on this board, I didn't know what I was talking about.

 

[etech]

Chess9, your last post makes it at least two by my unofficial count. Should we have a recount?

 

[chess9]

Etech:

If you only found two out of 2000, I'll take those odds. Please don't look any further.

 

[etech]

Ornery, you do know that you don't need a GFI for each receptcle. One at the beginning of a string of outlets will protect those "downstream". It depends on the way the GFI is wired whether it will protect the outlets downsteam, it's detailed in the wiring instuctions that come with them.

Just checking.

 

[etech]

Chess9, that was two out of the two in this thread. Batting 1000.
I won't look any futher.

 

[Ornery]

Yeah etech, that's what the first electrician told me too. He was really happy with being able to protect a whole house with these cheap, easily installed devices. I am too!

I'm going to buy a box of 10 or twelve of them and stretch them as far as I can. I'd like to replace a lot of these outlets just for aesthetic's sake. New plates, switches and outlets really finish off a room. I'd like to have grounded outlets everywhere, but if I try and sell the house, and it gets inspected by FHA, I think only GFI outlets would pass. I'd have to replace the other grounded outlets with the two conductor type. Hah, and those are twice the price of the grounded outlets!

 

[Mday]

what? i hope to learn some of that stuff in the coming years.... damn college