Do GFCI Outlets Need a Ground?

[Molo]

1. Do they work differently with a ground?

2. Are they less safe without a ground?

 

[ActionDave]

1. Do they work differently with a ground?

The stuff inside works the same with or w/o a ground but, instead of a ground wire telling the GFCI there is a ground fault and tripping it a person or thing has to become the ground fault before the GFCI will trip.

2. Are they less safe without a ground?

They are less safe without a ground, but they are more safe than an existing circuit with no GFCI protection.

 

[Sponsor]

 

[JWelectric]

1. Do they work differently with a ground?

No

2. Are they less safe without a ground?

No

 

[hj]

They are also supposed to be labeled "no ground wire" when used without one.

 

[DonL]

Without a Ground the Test button will not work.

 

[JWelectric]

Without a Ground the Test button will not work.

Yes it will

 

[DonL]

Yes it will

Then it is not a very good test.

How does it cause a ground fault with no ground ?

 

[ActionDave]

No

Yes they do. A GFCI with no egc can't sense a fault until a ground path is made.

No

GFCI is much safer than any circuit without one, yes but GFCI with a ground is best.

 

[ActionDave]

Then it is not a very good test.

How does it cause a ground fault with no ground ?

The GFCI has its own internal test circuit. It is the only approved test from the manufacture.

 

[Jadnashua]

A ground wire gives you a secondary means to provide a path that can trip a circuit breaker OR fuse if there is an overload. But, a GFCI works, and looks at, a different aspect - it is looking for an imbalance of current - IOW, if some of the current that should come out of the hot lead (then goes through the device) does NOT make it back to the neutral, then some of it had to leak somewhere (IOW, to ground). That current MIGHT have gone through you, and if it is large enough, it could kill you. The imbalance only needs to be 0.005A or 5 mA, WAY WAY to small to trip a circuit breaker, but a bit more could literally stop your heart. So, as has been said, you do NOT need a ground for a GFCI to work and provide the protection to life that it should. The circuit breaker is still a very useful device to protect the WIRING from burning up, but it's unlikely to protect YOU (other than maybe burning to death in the house fire if it was not there and something overloaded). Two different means of protection. There is a third one that has been mandated in many situations, and that is an AFCI - arc fault circuit interrupter. It looks for a loose connection that is arcing, and those arcs could start a fire, even though they are not drawing enough current to open a normal breaker.

 

[JWelectric]

There is some almost correct info in this thread. For the average layman there is an understanding of the protection given by a Ground Fault Circuit Interrupter.

A GFCI device has a computer chip installed that monitors the current between the current carrying conductors. On a 120 volt circuit the current leaves the transformer on one wire (black) coming through the service equipment, the branch circuit overcurrent device, down the conductor to the device, through the load, and back to the transformer through the grounded (neutral white) conductor. Both the black and white conductors are carrying current. Should for any reason the current have a difference on either of these conductors then the GFCI will open. No current on the EGC.

Install a GFCI device on a 20 amp circuit and load the device to 50 amps and the GFCI will not open. This is the job of the overcurrent device such as the breaker or fuse. Take the device out of its box and touch the brass screw with your thumb and the shiny screw with your index finger and the GFCI will not open. You are nothing more than a coffee maker or blow dryer that is connected to the load side of the device. Touch the black wire and the EGC and the device will open in 1/120th of a second. Yes it will hurt like a son-of-a-biscuit but it will open.

The Equipment Grounding Conductor plays no role what so ever in the function of a GFCI device. The device works the same with or without the EGC being connected. The device does not monitor the EGC for current. The purpose of the EGC is a low impedance path back to its source for fault current to travel in order to open the fuse or circuit breaker.

Understanding the trip curves of circuit breakers will show us that the EGC does little to protect us from shock. Each manufacturer of breakers will have a little difference in their trip curves. The trip curve is the amount of current and time it takes for the device to open.
As a general rule of thumb a breaker will fall under the following trip curves. For this we will use a 15 amp breaker. Load this breaker to 135% of its rating or 20.25 amps and if it opens in two hours then it fits the UL Standard by which they are to be made. This means that the EGC can have 20.25 amps flowing on it for up to two hours.

At 300% or 45 amps the breaker can take up to two minutes to open or the EGC could have up to 45 amps flowing on it for up to two minutes.
At 600% or 90 amps the breaker must open within two cycles or .033 seconds.

Compare this to the protection offered by a GFCI device that opens in one half of a cycle or 1/120th of a second without the use of an EGC. This is four times faster than a dead fault to the EGC and works without the EGC being in place therefore the EGC in no way makes a GFCI device any safer. It is not needed for a GFCI device to function.

There is a reason why the NEC will allow the replacement of a two wire receptacle with a GFCI device. I bet my bottom dollar that it is because the EGC plays no role in the function of the GFCI.

 

[DonL]

I do not even need a book to tell me a Ground is required in a three prong Outlet. You may get by with what hj said.

I guess they just added that connection because they had parts left over ?

In many places, If you update anything, You need to bring it up to the New codes.

And a Permit may be required. Many people just do it.

 

[Jadnashua]

It is legal and proper to provide personnel protection by retrofitting GFCI protection devices where you only have a 2-wire circuit IF you follow all of the installation instructions and that includes placing the little sticker on all of them, including the daisy-chained devices that can also now have a 3-wire receptacle that states "GFCI Protected - no service ground" or something to that effect. IOW, if you find the first receptacle in the chain, you can also replace ANY receptacles downstream with ground units for convenience and still maintain all of the personnel safety you had previously. Now, something like a surge suppressor may not work as well to protect things without a ground, but personnel protection is what the GFCI is providing, not equipment protection. On say a grounded tool, it would actually now be much safer even without the ground connection after installation of a GFCI.

If there's a short between the hot and ground or hot and neutral, or a leak (all it takes is more than about 5mA), even if there's no ground wire, the GFCI will open the circuit. So, if you understand, it remains as safe and actually is MUCH safer with the GFCI in there, even IF it also has a ground wire. The point being, unless the hot and neutral conductors are not balanced (everything going out comes back in), the device is not working properly and some is leaking to a ground - that ground does not have to be the equipment ground, and even if it is, the resistance back to the panel and the connection with the neutral would mean there would still be a current imbalance, and trip the GFCI.

 

[Vegas_sparky]

A GFCI will not trip if there is current flowing between hot/neutral. Fault or otherwise, is doesn't know the difference. If you have a damaged cord/piece of equipment, and the fault is between L-N, you better hope the breaker picks it up, and opens the circuit.

Years ago I broke one open to see its guts. I was amazed they were able to get a small CT(measuring balance between L-N), and the operating circuitry in such a small device.

 

[LLigetfa]

There is some almost correct info in this thread...

I read through this and did not find a description of how the TEST button works. There is conflicting information WRT the TEST button whether or not it will work in the absence of the protection ground.

There are testers that one can plug into a GFCI outlet and I presume that those testers redirect some small amount of current to the protection ground.

 

[Vegas_sparky]

The integrated test button still works without an EGC connected to the GFCI receptacle. All the test circuit has to do is send a small current around the CT from L-N, instead of passing through it, to create an imbalance in the CT. That test current should be calculated to within the trip ratings of the GFCI device.

I've never tested a GFCI with a plug tester that didn't have an EGC, so I can't comment on it's operation.

 

[hj]

quote; A GFCI will not trip if there is current flowing between hot/neutral. Fault or otherwise, is doesn't know the difference. If you have a damaged cord/piece of equipment, and the fault is between L-N,

IF there is more current being used by the hot side, than is flowing through the neutral side the GFCI WILL trip, because that indicates a "leakage" somewhere and it doesn't care where it is, i.e., in the equipment or through your body.

 

[Vegas_sparky]

I know how they work, and I should have added the word equal to make it perfectly clear.

The point was that a L-N fault will not be caught by a GFCI device.

 

[Jadnashua]

I know how they work, and I should have added the word equal to make it perfectly clear.

The point was that a L-N fault will not be caught by a GFCI device.

Not exactly...in fact, the fault is that some of the current fault path is through you or some other path and not entirely getting back to the neutral. I guess it is a matter of semantics. A EGC TO the GFCI is NOT required for it to work. An EGC is there to provide a secondary fault path for an overcurrent situation to trip the breaker or blow the fuse. Its presence will do NOTHING in most cases to protect you in the manner that a GFCI does. The fuse or CB will take many AMPS to remove power and could be the result of just plugging in too many things, and may not be a fault or safety hazard in the normal sense at all....a properly functioning GFCI only takes >5ma 'leaking' somewhere it isn't supposed to, and other than heating up the contacts which may weaken them, won't trip with overcurrent at all. IOW, it is not an overcurrent protection device, it is more of a misplaced current protection device designed to protect people and pets from potential harm. The CB or fuse is there to protect the wiring from overheating and burning down the structure, and other than that, isn't really designed as a first line people protector.

 

[Vegas_sparky]

NO, EXACTLY. We're going in circles. JW said it, and so did I. If you grab the Hot and neutral of a GFCI protected circuit, one in each hand, while totally isolated from ground, you are nothing but a resistor, and the GFCI will not trip while you're getting buzzed. If you're isolated from ground, what's going in you on the hot, will be going out of you through the neutral. The amount of current is dependant upon your bodies own electrical resistance. Wet hands will make it hurt a lot more. The device does nothing for a L-N fault, which can still occur under the right circumstance. Touch the hot of a GFCI protected circuit to a ground and you get a click from a tripped GFCI. Touch that same hot to its neutral, and you get a good pop, and the GFCI won't be tripped, the breaker will be.

I was describing a L-N fault. Interjecting a ground path is not part of what I'm describing.