# how a GFCI receptacle works if there is no ground wire connect to it?



## emtnut (Mar 1, 2015)

Here ya go :thumbsup:


http://lmgtfy.com/?q=how+does+a+gfci+work


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## Semi-Ret Electrician (Nov 10, 2011)

A GFCI simply measures the current entering the device and the current returning to the source. If it differs by more than 6 ma the device trips.


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## RePhase277 (Feb 5, 2008)

The GFCI measures the differential between the hot and neutral. The current is equal and opposite in a normally operating circuit so the difference is 0. If current takes a path outside of the intended circuit, more current will be flowing on one wire than the other and the GFCI will trip.


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## samgregger (Jan 23, 2013)

The same way it works when there is a ground connected to it.


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## LGLS (Nov 10, 2007)

Except w/o a ground the test button won't work.


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## RePhase277 (Feb 5, 2008)

LawnGuyLandSparky said:


> Except w/o a ground the test button won't work.


??:no:


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## Islander (Jul 11, 2016)

Some places still allow GFCI's to be installed in lieu of a wiring upgrade? Hmmm.


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## PlugsAndLights (Jan 19, 2016)

Islander said:


> Some places still allow GFCI's to be installed in lieu of a wiring upgrade? Hmmm.


Some places don't? 
P&L


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## Islander (Jul 11, 2016)

PlugsAndLights said:


> Some places don't?
> P&L


An electrician from Winnipeg was telling me that they banned those from being used in that circumstance. Maybe because so many homes there still have knob and tube wiring? I dunno.


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## ElectricalArtist (Jul 2, 2014)

A gfci is designed to protect against electrical shock. On a normal condition (no problems in circuit) , a 2 wire circuit, the amperage to the power supply (hot wire) is equal to the amperage returning to the power supply (nuetral) . If the difference between the current in the hot and nuetral is between 4 and 6 mill amps (.4 to .6) amps ,the gfci will open the circuit. Just a reminder if a gfci goes bad, it will still carry voltage and operate like a receptical but it won't trip under a unbalanced load. (Diffrence between grounded and ungrounded conductor)

You should always install a pig tail from the box to the receptical in this situation.


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## dmxtothemax (Jun 15, 2010)

When what you now know as a GFCI first came on the scene,
They did indeed monitor the current flowing in the earth wire.
These were know as earth leakage breakers.
But now days they use a different principle of operation.
Now they use a method called core balance relay.
Where they monitor the current flowing in the hot wire
And also monitor the current returning in the neutral line.
If all is well they should be exactly the same.
But if they are not because some is bleeding off to ground some where
Then it will trip out


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## Stickshaker (Jun 29, 2012)

LawnGuyLandSparky said:


> Except w/o a ground the test button won't work.


The gfci's test button will work, but not the button on a plug in gfci tester.


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## triden (Jun 13, 2012)

See that sensing circuit? If the current magnitude is the same in both L and N, the potential across the winding on the CT will be very close to zero as the fields will cancel. 

As L and N deviate and more current starts flowing through any one of the conductors, a voltage will be measured at the sensing circuit which is set to trip using a comparator with a reference voltage (usually 5mA or so).

You will also notice that the test button does not reference ground.


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## PlugsAndLights (Jan 19, 2016)

But will the test button on a hand held GFI tester trip the GFI if it's wired 
without a bond? :shifty:
P&L

edit: Sorry, already covered in post 13.


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## B-Nabs (Jun 4, 2014)

ElectricalArtist said:


> between 4 and 6 mill amps (.4 to .6) amps


You mean .004 and .006 amps.

Sent from my SM-G920W8 using Tapatalk


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## emtnut (Mar 1, 2015)

PlugsAndLights said:


> But will the test button on a hand held GFI tester trip the GFI if it's wired
> without a bond? :shifty:
> P&L
> .


Of course it will ! ... That's what the bootleg is for :jester:


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## brian john (Mar 11, 2007)

dmxtothemax said:


> When what you now know as a GFCI first came on the scene,
> They did indeed monitor the current flowing in the earth wire.
> These were know as earth leakage breakers.
> But now days they use a different principle of operation.
> ...


These were called ground return in the USA.


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## readydave8 (Sep 20, 2009)

ElectricalArtist said:


> You should always install a pig tail from the box to the receptical in this situation.


A pigtail from where to where?:confused1:


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## lighterup (Jun 14, 2013)

mike883 said:


> I got a question about replace the old house two slot receptacle(no ground wire inside),
> 
> normally, what we do is replace it with a GFCI receptacle, and label it with no equipment ground
> 
> ...


All of the above responses covered your question very well .

Your question exposes your own misunderstanding of the grounding
vs bonding.

The neutral is the primary "ground" and the bare copper (in NM cable) or green thhn in pipe & wire apps is for bonding any metal casings on 
equipment , devices and metal conduit.

The green / bare conductor is never intended for measurable "current". 
Without one , your plug in polarity tester should read "open ground"
not open "neutral" . This wording ma be whats throwing you off and
leading to this misunderstanding.

The bare equipment grounding is for (fault current) , not normal
return path to ground (neutral).

In a fault , contact of voltage to metal casings of devices & equipment
should go directly to ground @ an nonmeasurable speed ,opening the 
over protection device ( circuit breaker / fuse) so people , property and equipment do not get harmed.


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## Trigun1112 (Apr 13, 2017)

readydave8 said:


> ElectricalArtist said:
> 
> 
> > You should always install a pig tail from the box to the receptical in this situation.
> ...


A pigtail from the outlet ground terminal to the outlut box for a mechanical ground connection, assuming its a metal outlet box ofcourse.


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## readydave8 (Sep 20, 2009)

Trigun1112 said:


> A pigtail from the outlet ground terminal to the outlut box for a mechanical ground connection, assuming its a metal outlet box ofcourse.


I may be wrong but do not think that pigtail should be installed if no ground is present?


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## PlugsAndLights (Jan 19, 2016)

readydave8 said:


> I may be wrong but do not think that pigtail should be installed if no ground is present?


You're not wrong. connecting a bond from a receptacle to an unbonded 
box does no more good than connecting one end to the receptacle
and waving the other end in the air. 
In fact, the CEC disallows a bonding jumper in this situation. 
Code Ref: 26-700(9)


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## chicken steve (Mar 22, 2011)

GFCI's operate via a toroidal coil , or toroid

AFCI's operate on the same toroidal coil , save that they incorporate approx 1 and 3/4's (one is split)

This is the _heart_ of either unit, as well as function. One can make a rudimental one with parts laying around most shops.>>>










Further, it doesn't matter how much electronic _lipstick_ one places around a toroidal, it will _forever and a day_ only be able to 'sense' what a toroid can

~CS~


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## eyemxtinct (Apr 2, 2013)

RePhase277 said:


> The GFCI measures the differential between the hot and neutral. The current is equal and opposite in a normally operating circuit so the difference is 0. If current takes a path outside of the intended circuit, more current will be flowing on one wire than the other and the GFCI will trip.




You sure about that??? GFCI stands for "Ground" "Fault" "Circuit" "Interrupter".....don't see anything about hot or neutral on there.


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## PlugsAndLights (Jan 19, 2016)

eyemxtinct said:


> You sure about that??? GFCI stands for "Ground" "Fault" "Circuit" "Interrupter".....don't see anything about hot or neutral on there.
> 
> 
> Sent from my iPhone using Tapatalk


If you're in doubt, your best bet is to google "wikipedia GFCI" and 
read the article. It's worth reading. 
P&L

Edit: Just re-read the wikipedia page. It's not much help. Sorry.
Edit2: Here's a good article:
https://www.nema.org/Products/Documents/NEMA-GFCI-2012-Field-Representative-Presentation.pdf


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## RePhase277 (Feb 5, 2008)

eyemxtinct said:


> You sure about that???


Yep.


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## Switched (Dec 23, 2012)

mike883 said:


> I got a question about replace the old house two slot receptacle(no ground wire inside),
> 
> normally, what we do is replace it with a GFCI receptacle, and label it with no equipment ground
> 
> ...


This is almost always the first question I ask if you want a job with me. If you can't answer it I am not going to not hire you, but it tells me a lot about the fact that you are a Jman and can't seem to put in the time to learn the ins/outs of what we do. 

We don't all know all the answers, but for what we do (Primarily resi/commercial service work), you need to know some really good basics on explaining things to customers. 

Kudos to you though for posting here to understand it! Ask about the things you don't know, or you'll never know.:thumbsup:


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## chicken steve (Mar 22, 2011)

There's an urban legend that's circulated for years about a spark who insisted no ground need apply......

In attempt to prove it, he actually held the load side of *N* and *H* in each hand , allegedly flapped like a flounder until his better 1/2 turned off the juice....:no:


~CS~


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## eyemxtinct (Apr 2, 2013)

chicken steve said:


> There's an urban legend that's circulated for years about a spark who insisted no ground need apply......
> 
> 
> 
> ...




Well it makes perfect sense!!! 


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