Outlets wired in parallel

[don_resqcapt19]

Oh, and I stand corrected, its 6ma, not 5ma!

It is commonly stated as 5 mA because the UL standard say it must trip between 4 and 6mA.
Don

 

[charlie b]

So, in essence, when the load hands you 96? on the neutral, you quit loaning it money.

George, you are starting to think like me. That was exactly the type of analogy that I might have created. In fact, I think I'll wait a year or so, until everyone forgets having seen it here, then I'll copyright it. :wink: 8)

 

[ramdiesel3500]

George
I agree with Charlie! Excellent analogy!
I never thought of a GFCI as an electrical accountant!!!

 

[Awg-Dawg]

So, in essence, when the load hands you 96? on the neutral, you quit loaning it money.



That is the "dumbest" analogy I have ever heard.On that note,I will now begin using yours instead of mine.Mine takes 20 minutes and the recipiant always has a dumb look on their face when I am done.Bravo young George!!

 

[RUWired]

TIM,Stop being so cheap! If this is all in pipe and its a small office,you could have had your electrican pull all the "rag wire" out and replaced it all in the same amount of time we've been dicussing this.Plus you would have a full size ground,new wire, and new devices.The cost of the wire is minimum. Bring this up to date.
Rick

 

[aftershock]

The neutral of a circuit carries as much current as the hot conductor when a load is connected.

Imagine that you are the GFCI. Imagine that current is money. Your right hand is handing a dollar to the load in front of you, the load hides it for a second, and then returns the dollar back into your left hand. As you keep handing the load money, you're watching how much you're giving it, because you want it back.

So, in essence, when the load hands you 96? on the neutral, you quit loaning it money.

So, when the 4mA is lost between giving current out and getting it back, the GFCI trips. The grounding conductor had nothing to do with the transaction.

Hope that weird analogy helped, somehow.

Thamx for the lesson. I have been installing these things for over 6 yrs now. I always checked them using testers from Hot to Ground, if they trippped,, then they were working correctly. Therefore I *cough* assumed that it required a ground to work properly. Thanx again for opening my eyes.

 

[charlie b]

OK. I think the original question has been answered, so I don't feel bad about hijacking the thread. I want to ask a related question.

When my electrical contractor had finished the job, we had a discussion about GFCI receptacles and breakers. He said (much to my surprise) that if you take a wire, and short a GFCI receptacle's neutral and ground, the GFCI will trip. This is with no load on the circuit, nothing plugged into that outlet. I disagreed, since without a current-carrying load, there would be no difference in current for the GFCI electronics to sense, and therefore nothing to cause a trip.

So he did a test. He held a bare section of wire with insulated pliers, inserted the wire into the slots for neutral and ground, and sure enough the GFCI tripped. Can anyone explain why? I can only make a vague guess.

 

[jeff43222]

I've used that technique in the past myself. It's a quick way to test a GFCI if you have suspicions about the button or if the button is somehow unable to be used for the test (I see this from time to time). And whenever I have a GFCI that won't reset, the first thing I look for is a N-G short. That's almost always the culprit.

As for how it works, I suspect that induced voltage is the cause. Since the GFCI is supposed to trip at 4-6 milliamps, it wouldn't take much of a voltage difference between the neutral and ground to trip the GFCI when the two wires are shorted.

 

[Mike03a3]

OK. I think the original question has been answered, so I don't feel bad about hijacking the thread. I want to ask a related question.

When my electrical contractor had finished the job, we had a discussion about GFCI receptacles and breakers. He said (much to my surprise) that if you take a wire, and short a GFCI receptacle's neutral and ground, the GFCI will trip. This is with no load on the circuit, nothing plugged into that outlet. I disagreed, since without a current-carrying load, there would be no difference in current for the GFCI electronics to sense, and therefore nothing to cause a trip.

So he did a test. He held a bare section of wire with insulated pliers, inserted the wire into the slots for neutral and ground, and sure enough the GFCI tripped. Can anyone explain why? I can only make a vague guess.

I think this is your answer:

Grounded neutral. In a situation where the load side neutral is grounded and a ground fault also occurs, a parallel path through the GFCI for the ground fault current could exist. The portion of the ground fault current returning on the neutral conductor will not be sensed as differential current. This has the effect of desensitizing the GFCI. Therefore, the UL standard requires that GFCIs trip with a 6mA ground fault even when the neutral and ground are connected. To meet this requirement, GFCIs trip when the load side neutral and equipment grounding conductors are joined, even if there is no ground fault.

Taken from: Think like a GFCI

 

[chicar]

G.F.C.I. reads the grounded wire, not the gruonding wire. I would bond the recept box then make sure the pipe is bonded at the service to the grounded service wire.[neutral].

 

[chicar]

ooops. Did not realize there is another page.

 

[George Stolz]

I had lost track of this thread (still getting used to the new forum).

Many thanks for all the rave reviews!

Thanks to the forum, I learned how a GFCI works myself, so it's neat to have spawned a memorable analogy for it.

 

[sparky_magoo]

I never understood how a GFCI could detect a ground fault if there is no ground.

The GFCI can't detect a ground fault. the GFCI has a coil around the hot & neutral conductors. The magnetic field on each conductor is proportional to the current flow. The current on the hot & neutral are 90 degrees out of phase and will cancel each other out. If there is a parallel return path for either conductor, the current will be lower on the conductor with the fault or parallel path. Then the magnetic field on one conductor will be weaker than the other. In this case a current will be induced unto the coil around both conductors inside the GFCI. When this induced current reaches 4-6 mills, the GFCI trips because it is assumed a ground fault is present.

This principal is why you must separate the ckt. conductors before you use your clamp meter. If your clamp meter gives a reading when clamped around a cord, then you have a parallel current path.

 

[peter d]

The GFCI can't detect a ground fault. .

Ummmm....yes it can. If the current happens to be leaking to a grounding conductor or otherwise grounded surface, the GFCI will sense the imbalance and trip.

 

[sparky_magoo]

Is it actually detecting a ground fault or an imbalance in the current between the two conductors?

 

[LarryFine]

The current on the hot & neutral are 90 degrees out of phase and will cancel each other out.

180, actually.

Is it actually detecting a ground fault or an imbalance in the current between the two conductors?

The latter, which could be said to indicate the former.

 

[peter d]

Is it actually detecting a ground fault or an imbalance in the current between the two conductors?

The ground fault is the cause of the imbalance. So yes, the GFCI is detecting a ground fault. Hence the name.

 

[iwire]

Pete I agree with sparky_magoo, the electronics in a GFCI do not sense a ground fault.

Remember problems other than ground faults can also trip a GFCI. (Think neutrals tied together causing parallel paths)

GFCIs only 'know' that there is an imbalance in the circuit conductors.

Also many posters are forgetting that GFCIs do not need a neutral on the load side.

A GFCI may be straight 208-240 or 120/208-240 on the load side and still work properly. 8)

The neutral on the line side is simply there to power the electronics not provide any electrical reference.

 

[Jim W in Tampa]

It is a misleading name.Perhaps we should call it a current flow counter or CFC

 

[ramdiesel3500]

I think it should be called a DAG (disagreement/argument generator)!!!