Hello

Recently tried a "new to me" style of GFCI tester. The tester is a Klein RT250. It has several interesting features vs the ones I have when working as a maintenance electrician.

Tested several GFCI receptacles around the house. According to the manual a successful test will result in the display showing "000" (voltage) and "Open Hot".



A couple of the GFCIs did not test successfully as far as the reading on the tester. After pressing the test button the GFCI tripped but the result is a red indicator light and open neutral ground.



After further investigation with my Fluke DMM there is no actual voltage or open ground and neutral. I believe the tester is reading an induced voltage and giving a false reading (similar to when a volt tick gives a false reading).

Finally, with the tester showing the false reading and my Fluke DMM inserted into the same receptacle the false reading changes to "000" and "open hot". I believe this has to do with meters high impedance which is now in parallel with the tester.



Hoping someone could offer a more technical explanation of the last scenario.

Thank-you

 

Do you have an outlet tester (example below) to show if the outlet is wired correctly (i.e. hot, neutral, and ground going to the proper terminals)?
The one thing it can't show, is if the neutral and ground are reversed.

 

Do you have an outlet tester (example below) to show if the outlet is wired correctly (i.e. hot, neutral, and ground going to the proper terminals)?
The one thing it can't show, is if the neutral and ground are reversed.

View attachment 350669

I do not have one of those for home use as I would use the one from work. Retired late last year.

According to the manual the Klein RT250 does indicate "reversed hot/neutral". When I first encountered the "30V open ground neutral" I disconnected the receptacle to further troubleshoot with my Fluke DMM. Wiring of the receptacle was correct. No open ground or neutral found.

If there was a wiring issue I believe the GFCI tester, if working correctly, should indicate that before the test. The "30V open ground neutral" result comes after the GFCI tester "trips" the GFCI receptacle. I am fairly certain it is an induced voltage.

But why does the "30V open ground neutral" change to "000 open hot" on the tester when the DMM meter is inserted into the tripped GFCI at the same time?

 

Maybe I found the answer...

The tester trips the GFCI but because of an induced voltage/capacitive coupling in the GFCI circuitry the sensitivity of the tester indicates "30V open ground neutral".

Then when I insert the DMM into the same tripped GFCI it acts as a load that bleeds off the induced voltage?

 

the tester indicates "30V open ground neutral".
Then when I insert the DMM into the same tripped GFCI it acts as a load that bleeds off the induced voltage?

Perhaps.
But it could indicate an open ground.
Check the voltage and resistance between the neutral and ground.
It should be near zero for both.

 

Perhaps.
But it could indicate an open ground.
Check the voltage and resistance between the neutral and ground.
It should be near zero for both.

Post #1

"After further investigation with my Fluke DMM there is no actual voltage or open ground and neutral."

 

Consider that a GFCI does not need the third wire "ground" to sense and trip. That third-pin wire is there to satisfy the code, and in case the device fails. AND certainly a good DMM with the several megohm input can easily sense the capacity coupled voltage on an open circuit power cable. That is how I verify no shorts to ground.
In addition, an open circuited "ground " wire will have quite a few volts present from the live pair.