Will GFCI work with items without equipment ground

The GFI doesn’t rely on a ground, instead it will interrupt power where only a small potential exist between the hot and neutral sides of the receptacle...This is why they are sometimes so dang fussy...

3 tons wrote:
The GFI doesn’t rely on a ground, instead it will interrupt power where only a small potential exist between the hot and neutral sides of the receptacle...

What exactly does that mean ?

A GFCI detects a DIFFERENCE in current flow between the hot and neutral wires. That is, all the current going IN is not coming back OUT on the neutral like it should.....but presumably is finding it's own ground elsewhere.

So....operation with a 2 wire device is a bit iffy.
If the bowl of water it was dropped into is not grounded, then the detector likely wouldn't trip until a persons hand supplied a foreign ground....and maybe not then.

GFCI outlets measure the power being used on the "hot" power lead and ensure the same amount of power it flowing in the neutral. If a tiny amount of imbalance occurs, it's meant to interrupt the flow of power and keep you safe. If there's no ground wire and you complete a circuit to something that is grounded, it will interrupt just as quickly as if there was one. Some devices don't have a ground wire because they're "double insulated" and you're not supposed to be able to touch a "hot" metal piece on them.

mikestock wrote:
I know it's probably a dumb question but my wife's hair dryer is old and has no equipment ground. Wanted to be sure she is still protected if it should be dropped into water or otherwise shorted.

The GFCI would trip the circuit IF the water has at least a capacitive path, if not a conductive path, that would conduct at least 5 mA to Ground. IMO.

Yes an imbalance of 5ma between hot and neutral will trip the GFCI.
Does not matter where the power goes... the imbalance cuts power.
Ground pin is not required for GFCI to trip.

In truth. The GFCI is NOT there to protect YOU. It is there to protect the circuits. That by doing it's job, it also protects you, is just a bonus

Not sure if it still is, but adding a gfci outlet to a two wire system was a code approved way to add an outlet with a ground pin, even though it was not grounded.

Chris Bryant wrote:
Not sure if it still is, but adding a gfci outlet to a two wire system was a code approved way to add an outlet with a ground pin, even though it was not grounded.

yep, still permitted just need to add "no equipment ground" label to outlet.
Sam
Thanks to NECreader who commented on 2016/06/13:

This article should state that NEC 406.3 permits GFCI receptacles to replace two prong ungrounded outlets:

(3) Non–Grounding-Type Receptacles. Where attachment to an equipment grounding conductor 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.

Sam Spade wrote:

3 tons wrote:
The GFI doesn’t rely on a ground, instead it will interrupt power where only a small potential exist between the hot and neutral sides of the receptacle...

What exactly does that mean ?

A GFCI detects a DIFFERENCE in current flow between the hot and neutral wires. That is, all the current going IN is not coming back OUT on the neutral like it should.....but presumably is finding it's own ground elsewhere.

So....operation with a 2 wire device is a bit iffy.
If the bowl of water it was dropped into is not grounded, then the detector likely wouldn't trip until a persons hand supplied a foreign ground....and maybe not then.

It’s kinda amusing that nearly whatever someone says, one can reliably predict that it’ll be ardently challenged! - lol

Terryallan wrote:
In truth. The GFCI is NOT there to protect YOU. It is there to protect the circuits. That by doing it's job, it also protects you, is just a bonus

You have that backwards.

A CIRCUIT BREAKER OR FUSE is there to protect THE CIRCUIT (IE WIRING) from overloading which causes HEATING of the wires which eventually leads to failed insulation of the wires which eventually and ultimately leads to FIRE.

GFCI= GROUND FAULT CIRCUIT INTERRUPTER

GFCI is solely there to protect YOUR LIFE, not the electrical circuits.

GFCI do this by monitoring how much current is being drawn off of the HOT (black) wire and comparing the current that is being RETURNED to the power source breaker panel via the NEUTRAL (white) wire.

Things are well as long as the current is the same on BOTH HOT AND NEUTRAL.

Example, if a device plugged in is pulling 1A, there should be 1A on the HOT (Black) AND 1A on the Neutral (White).

IF a device plugged in is pulling 1A on the HOT (black) and the Neutral is measuring .995A that means there is .005A (5 MA) that is not "returning" via the Neutral (white) wire..

That 5 MA HAS to be going via a different route and that typically is YOU...

Your body because it is made up of WATER AND MINERALS makes a fantastic "resistor" and can easily conduct electricity..

Your do not WANT 5 MA of current flowing across your heart, it WILL KILL YOU..

In Tech school many, many yrs ago, we were taught when especially working on HOT chassis equipment to never use both hands, tuck one hand in your pocket.. Lest you become part of the circuit..

So, that is why we have GFCIs..

By the way, GFCIs now days are required to trip at 5 MA, older ones were 10 MA..