Does anyone know of a tester or simple (& safe) procedure that would verify operation of a GFCI receptacle on a 2 wire circuit?

Bill

hey bill, i don't know if this will help but when i use my GB Inst. circuit tracer on a line protected by gfci, as soon as i connect the transmitter to the circuit the gfci trips.
ken m

Ideal and GB both make a tester that will check the polarity of any receptacle as well as a button to check for GFCI protection. Relatively cheap unit and great for double checking receptacles after they have been installed. Home Depot has em' for 8.00. Check electrical testers.

[This message has been edited by elektrikguy (edited 08-09-2002).]

[This message has been edited by elektrikguy (edited 08-09-2002).]

The standard 3 prong polarity checking/GFCI testers will not trip a GFCI on a 2 wire circuit.

My understanding is that they try to divert some small amount of current to the Grounding conductor thereby tripping the GFCI. This doesn't work without a continuous ground path. (no ground wire)

My 'Wiggy' will trip a GFCI if tester is positioned between the 'hot' and any nearby grounded object.

My thoughts were if there was some easy way to recommend testing GFCI operation under these circumstances (2 wires) - or a better tester. There seems to be a lot of people that do not realize that the plug-in testers won't work and they think something is wrong with the GFCI or wiring. They are concerned that the GFCI will not trip because they cannot verify it with their tester.

Bill

Bill,

How about just running a suitable length lead to some convenient ground point and connecting it to the hot on the receptacle via a suitable value resistor?

You use 6mA as a trip point right? That works out as exactly 20K ohms at a nominal 120V. I'd probably choose something like an 18K resistor.

Paul,

Many people including Home Inspectors use these standard testers already, but do not know they are incapable of testing a GFCI on a 2 wire circuit. The following is an excerpt from an email I got today from a Safety Consultant about a situation where an Electrician installled GFCI receptacles as a way to get 3 prong outlets (on 2 wire circuits) and avoid the use of adapters: My question is if there is an easy way to tell this person (or others) how to test them and not just say "believe me, they'll work" ? It would have to be something simple with items readily available, or just a different/better tester.

Bill

Hmmm... I see the problem.

How about an adapter cable, 2-prong plug to a 3-prong grounded receptacle with a long clip lead for the ground connection?

Suitable instructions for use would need to be provided in layman's terms, but do you think that would still be too complex for some people?

Bill:
If there is not a grounded surface nearby in an older home and no equipment ground I think you would be hard pressed to be able to test a GFCI with out some kind of ground point.
Where I live it is standard practice to use the GFCI as stated in order to replace the old two wire receptacles with a 3-wire and no equipment ground.(labels applied accordingly) In that situation I dont see how you could test one. Now in the Bathroom that would be an entirely different story providing PVC hasnt replaced the original Galvanized pipe or copper.
Of course without a grounded reference point there is no danger of a shock in the first place and if there is none in the room why are they needed ?(Rhetorical Question)
Because the code wants to be all encompassing, and there is always the chance that the home could have hot-water or steam heat instead of forced-air, but if a forced air duct is in one of those rooms it could be used as a reference point. The FPN in 250.104 says to " Bonding all piping and metal air ducts wihtin the premises will provide additional saftey", if thats the case there should be a ' Ground Reference point' in each room. Presumeably.
Exccept for a Wiggy and some reference point I dont know of a tester that can test it without an egc.

Mark

Bill, since a GfCI is allowed to replace a two prong receptacle per the NEC we are to believe that a fault between ungrounded and grounding prongs would still activate the trip.

A standard recept tester might not be able to achieve this without the actual EGC being present, but if we were to take a cord cap and install a resistor or variable type device as Paul said between ungrounded and grounding prongs we would be able to provide a reliable test value. Have you tried the more expensive GFCI testers such as Hubbel or Bio Tek?

If we can not trip at these values, then we need to know why the false security from the NEC and manufacturers.

Roger

[This message has been edited by Roger (edited 08-09-2002).]

Rodger - The problem is the there is not grounding conductor present in these situations. There are only 2 wires present and no matter what tester you use and how you hook it up you will not trip the GFI. The only way to test the GFI is to have an additional wire. I have use an extension cord plugged into a different circuit that has a ground conductor and then connect a wiggy between the ground of the cord and the hot of the receptacle. The only way I know for these inspectors to test these devices would be to do something similar. They could use a grounding adapter that has a very long grounding lead connected to a know ground source on their plug in tester.

Curt

I have run into this situation with Home Inspectors for real-estate transactions.
They make a recommendation that a GFCI receptacle on an ungrounded circuit be grounded "in order for the GFCI to fuction properly".
It makes me want to scream.
I believe the ultimate test for the GFCI is the test button itself. It allows the test current to flow around the current sensor through a resistor, thereby creating a low-level imbalance between the 2 lines.
You'll have a hard time trying to convince some people who think they are "all that" with their little tester.
Bill,
This isn't necessarily simple, or safe but...
(Don't try this at home, kids)
On 2 occasions, I have taken an old line cord, jacket stripped about 12" and cut the neutral & ground at the jacket leaving 12" of (unstripped) hot lead.
After testing the GFCI with the button to verify it works, don gloves and drop the hot line into about 1" of water in the sink.
GFCI trips. Case closed. I'm a believer.

[This message has been edited by Redsy (edited 08-09-2002).]

Have not tried it, but thought about it.Fill the basin with water and toss the the hair dryer in. See what happens!! Atleast we will know from a safety stand point if it really works, not just what a tester may or may not say. Seriuously, I have wondered the same. Had someone suggest jumping the ground of a gfci to the neutral, once again never tried it.

Curt, This is exactly what I was pointing out. With out the EGC being present a typical analyzer will probably not work. The $100 Hubble variable level type or a iso tester such as Bio Tek makes would probably do the task.

Now, if in fact you need a conductor run from the neighbors house to test the GFCI, are we going to have it there when the actual event takes place?

This is my point, if it adds no more protection than any other two wire device, did the manufacturers push this requirement through?

Roger

On the other hand, if we are to live and breath by the NEC, and the AHJ can't make his or her own rules, we are complying regardless of this situation .

Roger

[This message has been edited by Roger (edited 08-09-2002).]

Jumping the ground to the noodle would allow the "bug" testers to work, but would be a terrible idea otherwise.

Uh, wouldn't it?

Also, GFCI's are absolutely needed in the absense of a true EGC... They still work, they detect any "missing" current over 6mA regardless of where it's going. No GFCI will prevent a noodle to hot shock, even with an EGC. Unlike the AFCI issue, this is a non-issue. They save countless lives and are proven (and rather simple) technology.

Just my $0.02.



[This message has been edited by sparky66wv (edited 08-09-2002).]

I have to agree with Redsky. Push the test button, ckeck for voltage. I remember a thread here or on another forum not too long ago about this subject. Someone said that the test button was accepted as a satisfactory method of testing both by the manufacturers and by an organization which I can't remember, seems like it was NFPA or UL.

Virgil,

I don't think connecting the grounding pin to the Grounded conductor would make a GFCI trip. The fact that current is diverted away from the 'Neutral' is what makes it trip.

Paul,

Is there a way that, through electronic components, an imbalance can be simulated and still only use 2 conductors?

Bill

hmm, isee $$$$ signs for the guy who can make a tester that you just plug in and it will test a 2 wire gfci. to the laboratory findo.

Step #1. Stand in bath of water holding the hot wire from a long extension cord. #2. Have an assistant plug in extension cord. #3. If you're still reading this far, the GFI works. But seriously.....

Virgil, temporarily linking the ground on the recept to the neutral wouldn't work, because the tester needs to divert current around the GFI to create an imbalance between hot and neutral. But as you said, you certainly wouldn't want to leave the jumper there.

If we were talking about a GFI recept rather than a GFI C/B at the panel, then you could temporarily jumper the recept ground to the supply-side neutral and the plug-in tester would work. But that's exactly what pressing the GFI's test button does, so why bother? All that the GFI test button does is connect a suitable value resistor from the load-side hot to the supply-side neutral (it would work the other way as well).

If an external test is really necessary, I think a long wander lead for the ground is the only practical (& safe) answer. Bear in mind that it wouldn't have to go to a grounding conductor or pipe etc. You could connect it to the neutral of a non-GFI'd circuit and it would work fine.

Bill,
I can't think of any practical way to set up an imbalance without having some other grounded reference point. With just two connections the current that comes out of one has to go back in the other, no matter what it goes through on the way. (That's why I can't figure how the "multicoupler" over on the other forum could have tripped the GFI).



[This message has been edited by pauluk (edited 08-10-2002).]

The simplest method I can think of right off the top of my head would be to use a Wiggy and an extention cord.

Plug the extention cord into an outlet which is either ahead of the GFCI, or on the opposite Ungrounded Line Conductor [other "Phase"], then test with the Wiggy between one terminal of the GFCI ["Hot" or "Noodle"] and whatever terminal on the cord that gets a complete circuit going.
That's about the most simple and least hazardous method I can think of right now [you have my interest on this big time!].

Alternate method, of course, is to find some Grounded Metal item and clip a long test cable to it, just to drive an unbalanced current through the GFCI device.

Using the idea behind random nuiscance trips when starting some Cap Start Induction Motors [I have heard of this and read of this, but never experienced it!], maybe there's a way to draw an imbalance of current through the GFCI device [possibly via one or more recepts on the load side] using various Reactive components - such as Capacitors and Inductors, possibly with a Variable Cap [like a tuning Cap], or a Variable Inductor [a "Variac" might work] - or both!

Maybe even some form of Tank Circuit between the GFCI device and "Downstream" receptacles would be able to either push an imbalanced current on one circuit conductor, or draw an imbalance on one conductor.

Trying to get a current above 6ma to flow - and not setup a hazardous situation - is the biggest problem to deal with [IMHO].
I could draw an imbalance of microamperes easilly, possibly reaching upto the 1.0ma range, just by connecting certain components to a circuit, then driving the current into the earth [dirt] either by a direct dirt connection, or on a nice damp concrete slab. That's just not gonna cut the mustard, though! [where did that term come from???]

Going to do some thinking and maybe even some smoke testing on this over the weekend.

Scott S.E.T.

OK, what I'm trying to say and what y'all are hearing are two different things...

Let me try again:

Connecting the white wire to both the green screw and the white screw on the line side of the GFCI will allow the testers to work but would be a bad idea otherwise... (I've seen it done, and it does allow the testers to work...)

Now does it make more sense, or have I fallen into an alternate universe with different laws of physics again?

With all the suggestions here, (using jumpers, test leads, etc...) I think the question of practicle test is being lost.

If the test button is not sufficient for the AHJ, yet the NEC allows this installation, we have a problem.

If we use special means (anything that would not be present under normal conditions) to test the device, we are in no way simulating a real incident. So what good would this be?

Roger

Thats a good point, in an area where there is no reference to ground there is no shock hazard. The GFCI will not trip on a line-Neutral fault, like our over priced AFCI. In those situations where there is no reference I tried everything to get it to trip with wiggy et al. I will have to try the 'Boot-leg' ground idea and see if that works. AT this point I dont see how it could the graound screw point is still open and it would seem reasonable that the current would just as likely return on the neutral than hang around at the green screw.

-Mark-

Looking back at the first post, I've just realized that Bill did specify "a GFCI receptacle" rather than "a receptacle on a GFI-protected circuit. So yes, in that case temporarily bridging the ground screw to the line-side neutral would allow the plug-in tester to check the GFI tripping.

However, as those cheap testers just connect a resistance from hot to ground to check tripping operation, the only thing this would prove over and above using the GFI's own test button is that there is continuity from the ground hole on the recept. to the green screw. (And as the GFI is on a 2-wire circuit, this doesn't matter as the ground screw won't be connected to anything!)

Scott,
I think you'll find the reason that motors etc. sometimes trip a GFI is due to capacitive coupling to the (grounded) frame. I can't see how any combination of reactive components should trip a GFI if just connected in any parallel or series combination between hot and neutral. There needs to be some sort of connection back to ground, be it a direct bond, resistance to ground, capacitive coupling, or whatever.

Roger,
From the practical point of view, I think the GFI's own test button is probably adequate for testing. It's just a simple momentary-contact switch and a resistor in series connected between load-side hot and line-side neutral, and as such is pretty fail-safe.

If any part of that test circuit goes open, the GFI won't trip when the button is pressed and will therefore signal that something is wrong. If the switch shorts out, the breaker will trip and not reset. If the test resistor drifts high in value, then the imbalance will be lowered and again, if it is too low to trip the user will still be alerted that something in the GFI is wrong, even if in this case it is only the test circuit itself.

Should we not be concerned with educating people that these GFI testers will not work properly when used on a GFI recept installed on an old 2-wire circuit? Come to think of it, are there any such warnings on the testers sold in Home Depot and such like?



[This message has been edited by pauluk (edited 08-10-2002).]

Paul,

To be practical, any solution would also have to work on a receptacle downstream from a GFCI receptacle too. So far it looks like the best answer we've got right now would be a tester with an additional testlead that can be clipped or touched to a nearby grounded object.

Bill

I know next to nothing about capacitors (never worked with them) so please forgive my ignorance. What would happen if you rigged up a capacitor with two switches, one between the hot wire and the capacitor and one between the neutral and the capacitor? With the neutral switch off and the hot switch on, if you plug a discharged capacitor in will it draw enough current to trip the GFI? Will it discharge if you turn the hot switch off and the neutral switch on?

Would it not be a good test just to make sure that when the test button is pressed that the gfci is actually off and not defective ?
Leviton has had problems with that, and upon reseting the gfci protection was gone but receptacle was hot. This would be especially true if there were no ground reference, at least the customer could be assured that the gfci were in place and YES it does work as it is suppose to.

-Mark-

Ah yes, for downstream recepts you'd have to go back to using a wander lead.

654,
I can't quite figure out how you envisage wiring the capacitor, but without some sort of ground reference it still wouldn't work.

A capacitor connected to AC will alternately become charged first one way then the other, giving the appearance of simply passing the AC. You could choose a capacitor which has the correct reactance at 60Hz to pass the 6mA or so of current needed, but you'd still need to reference it to ground (or pre-GFI neutral) for it to trip. And it really wouldn't have any advantage over a simple resistor.

I think you're getting at the idea of having a charged capacitor and letting it discharge into one side of the GFI to generate a pulse, right? Charging the capacitor from the recept would be easy enough (just use a rectifier diode in series), but you still couldn't discharge it through the GFI in an unbalanced way unless you have a separate reference point from somewhere else.

Nice try though!

Thanks Paul
Like I said, I don't know anything about capacitors. I was trying to come up with a way to draw current through the hot wire but have zero current on the neutral. Oh well

Paul, I agree whole heartedly that we should inform people, tradesmen and laymen, that these testers will not work on a two wire configuration. I have had to explain many times why they show open neutrals and grounds in isolation panels.

I remember checking a "GB 501" years ago, and I seem to remember the test button had a value of 7ma. (It's been a while and I may be wrong)

The good side of this problem is the testers show a problem, verses a good condition.

Now I will go back to my concern, if we can't establish a true value with out bringing supplementary help to play, we must wonder why the NEC allows this.

Redsy said he could drop the ungrounded conductor into a sink of water and trip the gfi, this is a good thing, but the amount of water, its chemical contamination, the sink itself, all come to play.

Paul, I need your help here, you have conducted test to the coefficient properties of unsalted and salted water.

In the case of Redsy's test, we couldn't in reality use this as a true test means could we? As far as any one using the sink itself I would say they would be covered, but a claw foot tub in a wooden structure?

Roger

Ah yes, plug-in GFI testers aren't usually sold in the DIY stores here, but the types with three lights to indicate possible wiring errors are common. I've lost count of the number of times I've tried to explain their limitations to people. One guy was panicking because his unit showed "line/earth reversed" in his RV and he thought the chassis was energized. Turned out it was just a broken neutral on the hook up, but because he had appliances connected in the vehicle, obviously the neutral to the tester was at 240V. But I digress....

The water test is certainly a "quick and dirty" method, but as you say, there are too many variables for it to be taken as evidence that the GFI will properly trip at 6mA. We have many old pressed steel and cast irons bathtubs here. If the tub is properly bonded, dropping a hot wire into the water is probably going to result in much more than 6 or 7mA.

The water in my area is so hard and full of minerals that I could easily get over an amp to flow through it without any trouble, so it would be no guarantee that the GFI would trip at the required 6mA level (or 30mA or whatever).

For my money, if the GFI's own test button trips it, I think there's little cause for concern. If we really need some form an external verification, then running a long wire to pick up a ground is the only practical way I can see to achieve it.

As you said though, at least in the case we're looking at the GFI won't trip so the homeowner/inspector should call in someone with the necessary knowledge to test the GFI another way.

Bill,

I've been using a "known ground". This isn't elegant, doesn't fit on the belt well, but this allows me to move on when I must verify GFI performance in 2-wire settings, knowing that the GFI works to spec.

I'll bring in a 50 or 100 foot cord from the truck, the one that is the best and I know is in great shape. I'll locate the laundry, kitchen, bath, 120 V AC or other newer hardwired grounded receptacle, plug in the cord and run it to the GFIs to be tested.

I'll put an adapter on the end of the GFI tester (the 3-prong cord cap to 2-wire receptacle adapter) and I use a bannana plug / alligator jumper to go from the cord ground to adapter.

Al

Hi.

Not sure if this will help any, but here's some information from CodeCheck about the possible DANGER of using a "DIY" tester:
http://www.codecheck.com/gfci_testing.htm

This link points to a PDF file for a device that has a retractable ground prong--not sure if that would still be able to simulate what is needed to "trip" the GFCI as was mentioned in this thread.
http://mitchellinstrument.com/c6046.pdf

P. S. I'm new to the forum...the bare wire into the sink part seemd a bit, um, shocking to me ;-)