Answer to a common question about GFCI's

[jtedesco1]

Hello:

Here's some information that will help answer the question asked of me last night while returning to my hotel in Albany, NY. I attended the local NACHI meeting and Joe Baranowski gave me a lift. This is for you Joe and anyone else who may have had the same question.


Question: Why can a GFCI receptacle be used in old two wire ungrounded circuits?

Replacement of receptacles shall comply with 406.3(D)(1), (D)(2), and (D)(3) as applicable.

(1) Grounding-Type Receptacles

Where a grounding means exists in the receptacle enclosure or a grounding conductor is installed in accordance with 250.130(C), grounding-type receptacles shall be used and shall be connected to the grounding conductor in accordance with 406.3(C) or 250.130(C).

(2) Ground-Fault Circuit Interrupters

Ground-fault circuit-interrupter protected receptacles
shall be provided where replacements are made at receptacle outlets that are required to be so protected elsewhere in this Code.

(3) Non–grounding-Type Receptacles

Where grounding means does not exist in the receptacle enclosure, the installation shall comply with (D)(3)(a), (D)(3)(b), or (D)(3)(c).


(a) A non–grounding-type receptacle(s) shall be permitted to be replaced with another
non–grounding-type receptacle(s).


(b) A non–grounding-type receptacle(s) shall be permitted to be replaced with a ground-fault circuit interrupter-type of receptacle(s). These receptacles shall be marked ``No
Equipment Ground.'' An equipment grounding conductor shall not be connected from the
ground-fault circuit-interrupter-type receptacle to any outlet supplied from the
ground-fault circuit-interrupter receptacle.


(c) A non–grounding-type receptacle(s) shall be permitted to be replaced with a
grounding-type receptacle(s) where supplied through a ground-fault circuit interrupter.
Grounding-type receptacles supplied through the ground-fault circuit interrupter shall be
marked ``GFCI Protected'' and ``No Equipment Ground.'' An equipment grounding

conductor shall not be connected between the grounding-type receptacles.

I am working on a short video clip and will try to make it available here if we can upload audio files or mpg files. If you are attending the convention I will have a table set up showing videos and items related to residential electrical inspections and existing installations and safety. I have images of the entire discussion available if anyone wants them.


I have a full schedule with the classes offered and will attend them so that I can learn more about the HI industry.


I will teach what I know if you will teach me what you know about the other areas beyond my expertise. I will be available anytime if you by me a beer!

[Timothy J. Gardner]

Joe,

Isn't the REASONING why because the GFCI still detects any current differential between the hot and neutral conductors, and trips if it is greater than 5 milliamps? (indicating current flow to ground other than through the neutral.)

tg

[jtedesco1]

Timothy:

Courtesy: www..nfpa.org

Ground-Fault Circuit Interrupter (GFCI).

A device intended for the protection of personnel
that functions to de-energize a circuit or portion thereof within an established period of time
when a current to ground exceeds the values established for a Class A device.

FPN: Class A ground-fault circuit interrupters trip when the current to ground has a value in the range of 4
mA to 6 mA. For further information, see UL 943,

Standard for Ground-Fault Circuit Interrupters.

The commentary following 210.8 contains a list of applicable cross-references for
ground-fault circuit interrupters (GFCIs). Exhibit 210.7 through Exhibit 210.15 contain
specific information regarding the requirements for GFCIs.
The FPN following the definition describes in detail how personal protection is achieved.

[Paul W. Abernathy]

That outlet is called a ground-fault circuit interrupter (GFCI). It's there to protect people from electrical shock, so it is completely different from a fuse in general.

A GFCI is much more subtle. When you look at a normal 120-volt outlet in the United States, there are two vertical slots and then a round hole centered below them. The left slot is slightly larger than the right. The left slot is called "neutral," the right slot is called "hot" and the hole below them is called "ground." If an appliance is working properly, all electricity that the appliance uses will flow from hot to neutral. A GFCI monitors the amount of current flowing from hot to neutral. If there is any imbalance, it trips the circuit. It is able to sense a mismatch as small as 4 or 5 milliamps, and it can react as quickly as one-thirtieth of a second.
So let's say you are outside with your power drill and it is raining. You are standing on the ground, and since the drill is wet there is a path from the hot wire inside the drill through you to ground. If electricity flows from hot to ground through you, it could be fatal. The GFCI can sense the current flowing through you because not all of the current is flowing from hot to neutral as it expects -- some of it is flowing through you to ground. As soon as the GFCI senses that, it trips the circuit and cuts off the electricity.

[Bob Badger]

Take a look at 250.114 for a list of items that can not be plugged into these GFCI protected non-grounded receptacles.