GFCI tester not tripping outlet, not a bootleg ground

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Old 04-02-19, 06:29 AM
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Question GFCI tester not tripping outlet, not a bootleg ground

Hi there,

I have a problem at my condo that is totally baffling me. The test button on a GFCI tester won't trip a particular GFCI outlet. Actually there are two GFCI outlets on that circuit and neither will trip. They are not in series but rather are in a star configuration, wired from an unknown upstream common point.

I have read a lot on that topic so here's what I tried so far:
  • Test button on both outlets works fine
  • Tested the GFCI tester at my house and it correctly trips a GFCI outlet
  • Tested for bootleg ground by disconnecting the white neutral at the main panel and testing for continuity between that disconnected white wire and ground. No continuity.
  • Tried swapping one GFCI outlet with another spare one I had (not new, unknown condition). Same problem.
  • One GFCI outlet has no load while the other one had a load connected (lights, this is a switched outlet). Disconnected the load. Same problem.

I'm rapidly running out of options to try. I could buy a brand new GFCI outlet but it seems unlikely that both GFCI outlets are defective. I also doubt that it's my tester that is defective because this problem was raised by the inspector during a pre-sale inspection.

Any ideas?
 

Last edited by Kadath; 04-02-19 at 09:28 AM. Reason: typo
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Old 04-02-19, 06:48 AM
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The circuit is probably ungrounded. Perhaps there is a segment of old ungrounded wire in there somewhere if this an old house, or perhaps the ground wire is disconnected or broken somewhere in the circuit.

A way to test for this is to turn the breaker off and remove the hot wire from the breaker. Go out to one of the GFCI boxes, and short the hot to the ground using a wirenut or a wire jumper. Back at the panel, measure resistance (ohms) from the disconnected hot and the ground bus. The reading should be single digit ohms if the ground is intact. If the reading is zero or infinity (depending on your meter), the ground is broken.
 
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Old 04-02-19, 08:18 AM
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If the test button on the GFCI works then the GFCI is functioning fine.
A plug in tester requires a ground to be present to test the GFCI. It needs to shunt a tiny current to ground to create the fault.
A GFCI on an ungrounded circuit is fine.

Does your tester show a good ground? Those tester usually light up two lights if the receptacle is wired properly.
 
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Old 04-02-19, 09:27 AM
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The tester did show a good ground (two lights), I forgot to mention that. Although perhaps the right light was a bit dim, hard to tell. However, I think that I will buy a new digital tester with leds, which seems able to better detect some ground faults from some reviews I read:
https://www.sperryinstruments.com/en...Outlet-Circuit

I will do the test that you suggest ibpooks.

The condo building was built around 1980.
 

Last edited by Kadath; 04-02-19 at 09:30 AM. Reason: typo
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Old 04-02-19, 11:50 AM
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The tester linked looks like it should show only one light when it is good. All the other lights indicate a fault.
 
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Old 04-02-19, 11:51 AM
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joed, that's the tester I'm planning to buy. The one I used is the standard 3 lights one.
 
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Old 04-03-19, 10:40 AM
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I think of two possibly explanations:

(1) The two GFCIs you have requires higher current to trip than the usual 5mA. I read that GFCIs for swimming pool require 20mA to trip.

(2) Your tester maybe providing slightly less than 5mA (e.g. 4.5mA), and therefore is able to trip some GFCIs but not some others.

Either way, I bet you can make these GFCIs trip with higher test current. So plug in a multi-outlet power bar and put 4 GFCI testers on it and push the test buttons at the same time -- this would provide 20mA test current. A cheaper solution than 4 GFCI testers is to buy a 5.6K ohm resister and put it between hot and ground to provide >20mA test current.
 
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Old 04-03-19, 11:18 AM
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Thanks GroundCurrent, that could indeed be the case. However I think that it's quite unlikely since the two GCFI outlets are of a different model. Maybe my tester is marginal as you say. In any case I'll buy another one tonight so I'll see.

I think the most likely explanation is that my ground is marginal. There's probably a connection since the right lamp was ON on the tester, but the ground resistance is probably too high. A high ground resistance would be in series with the resistance within the tester and will result in a lower test current, not tripping the GFCI.

I'll do the test that ibpooks suggested tonight. Then I'll know for sure. I could also use a 5.6k resistor and measure the current myself with a multimeter.

Now if the ground is indeed bad, hopefully I'll be able to fix it by re-tightening some screws. I can't really run a new wire without tearing apart the whole place.

Since the outlets are in a bathroom, could I possibly use copper pipes as a new source of ground?
 
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Old 04-03-19, 11:36 AM
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could I possibly use copper pipes as a new source of ground?
No. Code prohibits it. You can run a new ground from the breaker box or under newer code from nearest grounded outlet.
 
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Old 04-03-19, 12:38 PM
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No. Code prohibits it. You can run a new ground from the breaker box or under newer code from nearest grounded outlet.
Unless you are in Canada. Then it is permitted.
 
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Old 04-03-19, 12:41 PM
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From the ESA site. I have highlighted the important parts.


Question
I have purchased an older home that has older receptacles with no U ground slot. Can I replace them with modern grounding type receptacles?
Answer
It depends. Where grounding type receptacles (3 pin) are used to replace existing ungrounded type receptacles (2 pin), special caution must be exercised. The existing wiring supplying the receptacles may not incorporate a bonding conductor and the installation of a grounding type outlet may create a hazard if the outlet is not properly bonded to ground. Consult the service of a licensed electrical contractor.

The Code states "Where grounding type receptacles are used in existing installations to replace the ungrounded type, the grounding terminal shall be effectively bonded to ground." The Code permits bonding the receptacle by connection to a metal raceway or cable sheath that is bonded to ground; or by connection to the system ground by means of a separate bonding conductor; or by bonding to an adjacent grounded metal cold water pipe.

As an alternative to bonding the Code also states "grounding type receptacles without a bonding conductor shall be permitted to be installed provided each receptacle is protected by a ground fault circuit interrupter of the Class A type that is an integral part of this receptacle; or supplied from a receptacle containing a ground fault circuit interrupter of the Class A type; or supplied from a circuit protected by a ground fault circuit interrupter of the Class A type. Where this option is used, no bonding conductor is permitted between outlets unless that bond conductor is in turn connected to ground.

GFCI protection of the receptacles protects against possible shock hazards but does not provide a ground reference to the U-ground slot of the receptacles. Some appliances require a bond be connected to the U-ground slot in order to function properly. For example, surge protective devices for computer and entertainment equipment will not function without a ground reference.

Rule 26-700.

Ontario Electrical Safety Code 26th Edition/2015
 
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Old 04-03-19, 06:13 PM
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Thumbs up

So I was pretty sure the problem was a high resistance ground from you guys help but I got the better led tester anyway. Sure enough that one showed the bad ground while the dumb 3 lights tester was showing normal wiring.

So I started investigating at the first junction box. I was lucky and found a very loose ground screw right away. Retightened it and problem solved!

Thanks for everyone's help.
 
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