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#12440 - 08/09/02 02:55 PM Practical test for GFCI on 2 wire circuit  
Bill Addiss  Offline
Joined: Oct 2000
Posts: 3,878
Does anyone know of a tester or simple (& safe) procedure that would verify operation of a GFCI receptacle on a 2 wire circuit?


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#12441 - 08/09/02 04:24 PM Re: Practical test for GFCI on 2 wire circuit  
ken m  Offline
Joined: Aug 2001
Posts: 58
south carolina
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

#12442 - 08/09/02 04:34 PM Re: Practical test for GFCI on 2 wire circuit  
elektrikguy  Offline
Joined: May 2002
Posts: 132
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).]

#12443 - 08/09/02 05:46 PM Re: Practical test for GFCI on 2 wire circuit  
Bill Addiss  Offline
Joined: Oct 2000
Posts: 3,878
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.


#12444 - 08/09/02 06:19 PM Re: Practical test for GFCI on 2 wire circuit  
pauluk  Offline
Joined: Aug 2001
Posts: 7,520
Norfolk, England

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.

#12445 - 08/09/02 07:11 PM Re: Practical test for GFCI on 2 wire circuit  
Bill Addiss  Offline
Joined: Oct 2000
Posts: 3,878

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:
I recently revisited this employer and there are GFCI receptacles in the upstairs which was supposedly installed to correct the original condition. OF COURSE I tested several receptacles and they all reflected an open ground and would not trip with my receptacle tester, testing for ground fault. I wrote it up. Now I have a copy of the letter the contracting electrician sent to the city stating that NEC Article #406.3, D 3 (b & c) allows this type action. The problem I have is that the GFCI receptacles would not trip, so where is the protection? Is that OK or is there something else that this electrician could or should have done? The municipality sent the electricians letter to the building inspector and the building inspector stated that it was OK.....but I still have my doubts. Is this acceptable or is this a violation? I must have been born in Missouri and my Mother never told me!!
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.


#12446 - 08/09/02 07:31 PM Re: Practical test for GFCI on 2 wire circuit  
pauluk  Offline
Joined: Aug 2001
Posts: 7,520
Norfolk, England
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?

#12447 - 08/09/02 07:44 PM Re: Practical test for GFCI on 2 wire circuit  
motor-T  Offline
Joined: Nov 2001
Posts: 280
Girard, Ohio, USA
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.


#12448 - 08/09/02 08:17 PM Re: Practical test for GFCI on 2 wire circuit  
Roger  Offline
Joined: May 2002
Posts: 1,716
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.


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

#12449 - 08/09/02 09:02 PM Re: Practical test for GFCI on 2 wire circuit  
caselec  Offline
Joined: Apr 2002
Posts: 558
San Jose, CA
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 Swartz

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