GFCI & Plug Tester

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Little Bill

Moderator
Staff member
Location
Tennessee NEC:2017
Occupation
Semi-Retired Electrician
Why would a GFCI receptacle trip when a plug tester is plugged in? The tester does have a GFCI tester button on it. At first I thought I was hitting the button when plugging it in because I have done that before. The button is right on top and is easy to have your hand on it when plugging it in.
But I carefully plugged it in, making sure I wasn't touching the button. As soon as it's inserted the GFCI trips.

The recep will hold after unplugging the tester but as soon as you plug it back it trips. I started to start tearing things apart to look for a fault then I realized they had been using that recep and it didn't trip. I then took another tester without a GFCI test button and plugged it in and it held. So I plugged a load in and it held.
So why was it tripping with the tester w/GFCI test button?
 

growler

Senior Member
Location
Atlanta,GA
I would try that same tester on other GFCI protected receptacles and see what results you get. Also I would use a different plug in tester with test button on that receptacle.

If I can prove to myself the tester is bad then in the trash it goes.
 

Little Bill

Moderator
Staff member
Location
Tennessee NEC:2017
Occupation
Semi-Retired Electrician
Ok, I brought my tester in the house and checked it on my GFCI receps. Works like it should!

The house I tried to use it on had old GFCIs. Maybe the old ones don't play well with the testers?

I can't really just go back where I was because it's about an hours drive from me. I was finishing up a remodel and had to check some circuits that the GC couldn't get the lights to work. So I'm finished there for now.
 

JFletcher

Senior Member
Location
Williamsburg, VA
Ok, I brought my tester in the house and checked it on my GFCI receps. Works like it should!

The house I tried to use it on had old GFCIs. Maybe the old ones don't play well with the testers?

I can't really just go back where I was because it's about an hours drive from me. I was finishing up a remodel and had to check some circuits that the GC couldn't get the lights to work. So I'm finished there for now.

Older GFCIs can fail innumerable ways. There's also the possibility the teser had something stuck in/holding down the test button at the remodel that worked its way loose between the remodel and your house.
 

Little Bill

Moderator
Staff member
Location
Tennessee NEC:2017
Occupation
Semi-Retired Electrician
That makes no sense, GFCIs are pretty basic straight forward gizmos.

I've seen the old ones do some strange things. They used to fail "closed" .
All I can tell you is the tester tripped the old GFCIs and didn't trip mine that are less than a year old.
 

iwire

Moderator
Staff member
Location
Massachusetts
I've seen the old ones do some strange things. They used to fail "closed" .
All I can tell you is the tester tripped the old GFCIs and didn't trip mine that are less than a year old.

Where the GFCIs at this other location working with other loads plugged in?

I am still leaning towards bad tester, just the button sticking closed on it could do it. (And unsticking on your ride home) Loose conductive material floating around inside the tester etc.

But stuff happens so who knows? :)
 

kwired

Electron manager
Location
NE Nebraska
The standard has always been 4-6 mA unbalance will cause tripping. The improvements over the years involved fail safe types of improvements to help prevent from having a unit fail closed or to prevent line/load supply connections being reversed, another improvement was to make them more resistant to nuisance trips because of "inductive kickback".

20k ohm or less between "hot" and EGC on your tester terminals should trip a properly working GFCI, so should any N to EGC fault.
 

Little Bill

Moderator
Staff member
Location
Tennessee NEC:2017
Occupation
Semi-Retired Electrician
Where the GFCIs at this other location working with other loads plugged in?

I am still leaning towards bad tester, just the button sticking closed on it could do it. (And unsticking on your ride home) Loose conductive material floating around inside the tester etc.

But stuff happens so who knows? :)

As I mentioned earlier, I remembered they had been using the receptacle. But to be sure I plugged in a shop vac and it held and ran the vac.
 

goldstar

Senior Member
Location
New Jersey
Occupation
Electrical Contractor
I can remember a hair dryer that my wife had that had a built-in GFI plug. Each time it was plugged into a receptacle (GFCI or not) the GFI at the plug would trip. Hit the reset button and the dryer worked - no problem. Removed the plug and it remained in the un-tripped mode until the next time it was used.

Why am I telling you this ? You mentioned that the GFCI's were old. Perhaps they weren't purchased at a local supply house but from a hardware store that purchased some that were manufactured in some third world country. Over the years I'm sure we've all seen various design changes on GFCI receptacles :
  • They started out having only test and reset buttons. No indicator LED's
  • Then they had indicator LED's to show it was powered on and ready to go
  • Then they changed and had the indicator LED's showing that the unit was tripped - no power on LED
  • Then they changed and had dual color LED's showing either tripped (yellow) or (red) end of life cycle
  • The last set of cheap and dirty GFCI receptacles that I purchased from Barnet Supply had only red LED's indicating end of life
The long and short of this is that if the GFCI functions properly when tested then so be it. It may have been a design issue at the time of manufacture, IMHO.
 

George Stolz

Moderator
Staff member
Location
Windsor, CO NEC: 2017
Occupation
Service Manager
I'm just trying to wrap my mind around owning a plug checker long enough to use it up - I'm pretty sure I've lost every plug checker I've owned long before I had a chance to wear it out. :D
 

JFletcher

Senior Member
Location
Williamsburg, VA
I'm just trying to wrap my mind around owning a plug checker long enough to use it up - I'm pretty sure I've lost every plug checker I've owned long before I had a chance to wear it out. :D

Mine winds up in the bottom of the toolbag with missing covers on the lights, then busted lights. The last one I had did the same, had me scratching my head when I tested an outlet and got open neutral, then another the same, then another. blown bulb.

NC testers arent much better. nearly got lit up relying on it last week; best I can figure, something sat on top of the light button overnight and killed the brand new AAA batteries. Check it before you get 50' into a tight nasty crawlspace. :D
 

kwired

Electron manager
Location
NE Nebraska
I can remember a hair dryer that my wife had that had a built-in GFI plug. Each time it was plugged into a receptacle (GFCI or not) the GFI at the plug would trip. Hit the reset button and the dryer worked - no problem. Removed the plug and it remained in the un-tripped mode until the next time it was used.

Why am I telling you this ? You mentioned that the GFCI's were old. Perhaps they weren't purchased at a local supply house but from a hardware store that purchased some that were manufactured in some third world country. Over the years I'm sure we've all seen various design changes on GFCI receptacles :
  • They started out having only test and reset buttons. No indicator LED's
  • Then they had indicator LED's to show it was powered on and ready to go
  • Then they changed and had the indicator LED's showing that the unit was tripped - no power on LED
  • Then they changed and had dual color LED's showing either tripped (yellow) or (red) end of life cycle
  • The last set of cheap and dirty GFCI receptacles that I purchased from Barnet Supply had only red LED's indicating end of life
The long and short of this is that if the GFCI functions properly when tested then so be it. It may have been a design issue at the time of manufacture, IMHO.
Portable GFCI's often are and have been required to trip when power is cycled, chances are the circuit is opened when you lose voltage but not all mechanical aspects of kicking out the test button are completed for some reason until voltage is restored?
 
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