GFCI's do not need an EGC (moved from another thread)

[crossman]

Would this trip a GFCI?

Yours won't. But I think mine will:

 

[crossman]

ELA's diagram shouldn't trip the GFCI because the current generated through the xfmr action will show up in all portions of the circuit, both hot and neutral.

 

[480sparky]

Yours won't. But I think mine will:

Change the battery to a resistor. Same result.

 

[crossman]

Change the battery to a resistor. Same result.

You are correct.

 

[weressl]

Yours won't. But I think mine will:

Yep, it sure shorts out the battery

 

[crossman]

Yep, it sure shorts out the battery

No problem shorting out the battery. As indicated by the level of current flow, it has an internal resistance that limits the current flow.

But does it trip the GFCI?

 

[weressl]

No problem shorting out the battery. As indicated by the level of current flow, it has an internal resistance that limits the current flow.

But does it trip the GFCI?

Indicated where? By what?

Laptop batteries may have integral regulators, but ordinary battery short circuited sure spells disaster.

DC current will not activate an AC current sensor as a normal course of design. There would be no reason to design it that way. If someone is familar with the board level design of the electronics they would be able to tell.

The rise of the current at the time of switching in an inductive detection circuit MAY activate, but it is a hit and miss.

 

[gar]

080722-0944 EST

A resistor from the hot input to the hot output instead of the battery may or may not trip the GFCI. This will depend upon the value of the resistor. Note: between the hot in and out there is a wire passing thru one or two current transformers and a relay contact. The external resistor is in parallel with the internal wire which is a very low resistance. The external resistor has to be low enough to remove 5 MA or more current from the straight thru wire.

In contrast when a 12,000 ohm resistor is placed from hot in to neutral out and the supply is 120 V, then there is 10 MA of unbalanced current.

I concur with crossman that the AC induced current from the current transformer in the neutral output line will not trip the GFCI because it does not produce an unbalanced current between hot and neutral.

.

 

[crossman]

Indicated where? By what?

The lower right hand portion of the diagram.

Laptop batteries may have integral regulators, but ordinary battery short circuited sure spells disaster.

I am shorting out a AA battery right now as I am typing this. No disaster has occurred. I am alive and well. It did not even burn my fingers.

DC current will not activate an AC current sensor as a normal course of design. There would be no reason to design it that way.

Would there be a reason not to design it that way? I imagine that the designers never even considered what is happening and the diagram, so I doubt they would intentionally design the circuit to avoid tripping with the battery applied.

I still bet that it will trip. I may be wrong. But I am still going with "trip".

Edit: removed extraneous quote

 

[weressl]

The lower right hand portion of the diagram.



I am shorting out a AA battery right now as I am typing this. No disaster has occurred. I am alive and well. It did not even burn my fingers.



Would there be a reason not to design it that way? I imagine that the designers never even considered what is happening and the diagram, so I doubt they would intentionally design the circuit to avoid tripping with the battery applied.

I still bet that it will trip. I may be wrong. But I am still going with "trip".

Edit: removed extraneous quote

The current will flow between the positive and negative poles of the battery through various paths in proportion of their resistance. Although some of the current will follow the path of the 'long way' through the load that you called resistor and through the power source winding, but the majority will flow through the shortest path across the GFI.

Try serching Google for battery short circuits, you will see some interesting videos.

The designers would design for the application, that is AC, therefore their focus would be to detect AC current not DC. That is why the original argument for using the battery was bogus as it intended to defeat a definition that is part of the design criteria.

I am ambivalent about the trip.no trip issue. It is simply immaterial to the functioning of the unit, unpredictable even with the avalibale hypothesis since we do not have sufficient data to determine it with any confidence.

 

[charlie b]

. . . but the truth is, under a 590 application and an assured grounding program in place, GFCI's are not necessary because in the event of a ground fault most of the current will be shunted around the user.

With a correctly installed and functioning EGC, there should not be a hazardous voltage and if there is, there will be enough current flowing to get into the instantaneous trip range of the breaker so the hazard will not exist for long.

Let me offer the possibility that a person might come into contact with an energized portion of a piece of equipment, without there being any contact between that same energized portion and the external metal parts to which the EGC is connected. I know, the case is supposed to be on the outside, and you are not supposed to open the case to reach inside. But it can happen; it has happened.

I changed my views of the nature of fault current and the hazards of commonplace electrical stuff about five or six years ago, when I read a short article from a Chicago area newspaper. I have added this story to the training class that I had developed on the topic of electrical theory. I have also gone on a minor campaign to teach people the importance of installing GFCI protections for all receptacle outlets outdoors (even if the grandfather rule would not require them in your house).

A woman was electrocuted while operating a weed cutting tool in her yard. The grass was wet, and the extension cord had been damaged. The fatal current path was from the breaker panel to the hot pin of the receptacle, through the ungrounded conductor of the extension cord, to the water that had entered through the break in the cord’s insulation, through water or dirt that had accumulated along the outside of the cord, into her hands, through her body, into the dirt beneath her feet, through planet Earth to the ground rod, up the GEC to the service panel, via the N-G bond point back to the service’s grounded conductor. The external case of the tool may or may not have been metal, and the cord may or may not have included a EGC. It would not have mattered. A GFCI would have saved her life, but an EGC would not have.

 

[weressl]

080722-0944 EST
I concur with crossman that the AC induced current from the current transformer in the neutral output line will not trip the GFCI because it does not produce an unbalanced current between hot and neutral.

.

We had issues with HRG(High Resistance Grounding) false high ground current indication with ASD's. It is a complex issue with harmonics introduced by the rectifier front ends. Needless to say that the manufacturer needed to change their sensing circuits to sensors with harmonic restraint to properly function.

We had issues with certain UPS's that were NOT designed to be used for HRG systems and also ASD's that needed to have adjustments when used on HRG.

I know this is somewhat off the topic as HRG fault sensors are a different type GFI, but I am trying to highlight how complex loads can affect the circuit operation of other less-than-simple sensors or detectors.

 

[weressl]

Let me offer the possibility that a person might come into contact with an energized portion of a piece of equipment, without there being any contact between that same energized portion and the external metal parts to which the EGC is connected. I know, the case is supposed to be on the outside, and you are not supposed to open the case to reach inside. But it can happen; it has happened.

I changed my views of the nature of fault current and the hazards of commonplace electrical stuff about five or six years ago, when I read a short article from a Chicago area newspaper. I have added this story to the training class that I had developed on the topic of electrical theory. I have also gone on a minor campaign to teach people the importance of installing GFCI protections for all receptacle outlets outdoors (even if the grandfather rule would not require them in your house).

A woman was electrocuted while operating a weed cutting tool in her yard. The grass was wet, and the extension cord had been damaged. The fatal current path was from the breaker panel to the hot pin of the receptacle, through the ungrounded conductor of the extension cord, to the water that had entered through the break in the cord?s insulation, through water or dirt that had accumulated along the outside of the cord, into her hands, through her body, into the dirt beneath her feet, through planet Earth to the ground rod, up the GEC to the service panel, via the N-G bond point back to the service?s grounded conductor. The external case of the tool may or may not have been metal, and the cord may or may not have included a EGC. It would not have mattered. A GFCI would have saved her life, but an EGC would not have.

Thanks Charlie for supplying a real life example of what I was trying to explain.

 

[wptski]

I had two AA Ni-MH cells in a plastic holder one time and accidentally shorted the contacts. It actually melted the spring contact right through the plastic, opening the circuit up.

A high resistance cell can't deliver many amps. If you measured the resistance of a car start battery, it would be around 1-2 milliohms.

 

[crossman]

The battery in my diagram is delivering 30 mA while shorted out. Laszlo's video reference to the dangers of battery explosions, and the power contained within a car battery are well known. These facts, however, have no bearing on the point at hand.

I still think the GFCI will trip. But as Lazslo inferred, my conjecture is purely anecdotal.

Now, no one has pointed out that there are issues with the battery if the GFCI does trip.

 

[480sparky]

No problem shorting out the battery. As indicated by the level of current flow, it has an internal resistance that limits the current flow.

But does it trip the GFCI?

Possibly. The battery is simply a parallel portion of the circuit, so some current would flow. Depending on the resistance of the battery, if the current flow through the battery exceeds the trip rating of the GFI, then it will trip.

 

[crossman]

if the current flow through the battery exceeds the trip rating of the GFI, then it will trip.

The measured current from the battery is 30 mA.

 

[LarryFine]

Would this trip a GFCI?

It shouldn't.

 

[mivey]

It shouldn't.

You are correct. You can't "inject" current into the circuit because you would violate Kirchoff's Current Law. The conductor is not a hose, even though some water analogies work fine for some limited cases.

 

[mivey]

This may be ELA had in mind: