Question for ATOT electricians

[HappyPuppy]

Will GFIC outlets only work with three wires? My house is very old and wired with the old cloth covered post and knob wiring. There are only two wires to each switch and outlet. Is the ground wire, the 3rd wire, necessary for a GFIC to function properly?

 

[MercenaryForHire]

Originally posted by: HappyPuppy
Will GFIC outlets only work with three wires? My house is very old and wired with the old cloth covered post and knob wiring. There are only two wires to each switch and outlet. Is the ground wire, the 3rd wire, necessary for a GFIC to function properly?

GFCI, and yes.

- M4H

 

[HappyPuppy]

Originally posted by: MercenaryForHire

Originally posted by: HappyPuppy
Will GFIC outlets only work with three wires? My house is very old and wired with the old cloth covered post and knob wiring. There are only two wires to each switch and outlet. Is the ground wire, the 3rd wire, necessary for a GFIC to function properly?

GFCI, and yes.

- M4H

I was afraid of that. Now I have to run new wiring to the bathroom. :|

Thanks.

 

[MercenaryForHire]

Originally posted by: HappyPuppy

Originally posted by: MercenaryForHire

Originally posted by: HappyPuppy
Will GFIC outlets only work with three wires? My house is very old and wired with the old cloth covered post and knob wiring. There are only two wires to each switch and outlet. Is the ground wire, the 3rd wire, necessary for a GFIC to function properly?

GFCI, and yes.

- M4H

I was afraid of that. Now I have to run new wiring to the bathroom. :|

Thanks.

If it was any other room I might play Devil's Advocate and suggest a more stopgap solution, but when there's that much water involved, no fvcking around.

- M4H

 

[Analog]

Originally posted by: HappyPuppy
Will GFIC outlets only work with three wires? My house is very old and wired with the old cloth covered post and knob wiring. There are only two wires to each switch and outlet. Is the ground wire, the 3rd wire, necessary for a GFIC to function properly?

No, the third wire (GND) is not required. The way a GFCI works is that it compares the amount of current flowing through the hot lead, and the neutral. If they are not equal, then the difference is leaking through to ground, or through a person to ground. At a certain level, the GFCI outlet then trips, to protect the person from being shocked. As you can tell from this description, the third wire has nothing to do with it at all.

A properly wired house will have grounds available, so that chassis are grounded and provide safety by not allowing energized chassis, if an internal short occurs in an appliance. In your house, if your washer, for example, develops an internal short, the chassis may become energized, thus shocking the hell out of you when you touch it. If it had the third wire, then the chassis would have been grounded, and the short would have taken the breaker out - informing you of a problem. HTH.

 

[DrPizza]

Really? I'm not positive that they wouldn't work without the ground - From the way they operate, I'm pretty sure they should work. However, in the locations where a GFCI would be necessary, I also think a ground is pretty important as well.

 

[DrPizza]

Yeah, I looked. It doesn't sense the current in the ground wire. It compares the current between the neutral and the hot wire. Any mismatch of 3 or 4 milliamps and it trips the GFCI breaker in about 1/30th of a second. If it were to rely on checking the ground wire, it wouldn't provide protection from electrocution - in the case of electrocution, the current would be flowing through the victim, rather than the ground wire.

 

[HappyPuppy]

Originally posted by: yellowfiero

Originally posted by: HappyPuppy
Will GFIC outlets only work with three wires? My house is very old and wired with the old cloth covered post and knob wiring. There are only two wires to each switch and outlet. Is the ground wire, the 3rd wire, necessary for a GFIC to function properly?

No, the third wire (GND) is not required. The way a GFCI works is that it compares the amount of current flowing through the hot lead, and the neutral. If they are not equal, then the difference is leaking through to ground, or through a person to ground. At a certain level, the GFCI outlet then trips, to protect the person from being shocked. As you can tell from this description, the third wire has nothing to do with it at all.

A properly wired house will have grounds available, so that chassis are grounded and provide safety by not allowing energized chassis, if an internal short occurs in an appliance. In your house, if your washer, for example, develops an internal short, the chassis may become energized, thus shocking the hell out of you when you touch it. If it had the third wire, then the chassis would have been grounded, and the short would have taken the breaker out - informing you of a problem. HTH.

Your explanation sounds reasonable, although M4H disagrees. Are you an electrician or EE? I am remodeling an upstairs bathroom and will be installing a new outlet. It has to have a GFCI to be to code, as well as for safety.

As I said in my OP, my house is 100+ years old and has but 2 wires to each outlet and switch. Running new wiring is going to be a major PITA.

 

[Analog]

I am a professor of EE, and a licensed electrician.