GFCI Failure Modes

[Marty Lustig]

I disassembled a "failed" GFCI. (If you've not done so, I strongly encourage it....they are complex.)

There are "springy" metal contacts that open when the GFCI trips. On both sides (hot and "neutral") there was evidence of considerable arcing and heating. There was extensive pitting....and i'm inferring that was caused by arcing. Heating is evidenced by small amount of melted plastic where the "springy" metal contacts rest on a plastic wedge. (The wedge slides to open the circuit by raising the "springy" metal contacts....away from a mating contact.)


MY QUESTION: What could have caused the arcing? My only conclusion so far is that something that was drawing significant current (and developed a ground fault after operating for some amount of time, perhaps even a few seconds) caused the GFCI to trip. Any other thoughts??

 

[kwired]

I disassembled a "failed" GFCI. (If you've not done so, I strongly encourage it....they are complex.)

There are "springy" metal contacts that open when the GFCI trips. On both sides (hot and "neutral") there was evidence of considerable arcing and heating. There was extensive pitting....and i'm inferring that was caused by arcing. Heating is evidenced by small amount of melted plastic where the "springy" metal contacts rest on a plastic wedge. (The wedge slides to open the circuit by raising the "springy" metal contacts....away from a mating contact.)


MY QUESTION: What could have caused the arcing? My only conclusion so far is that something that was drawing significant current (and developed a ground fault after operating for some amount of time, perhaps even a few seconds) caused the GFCI to trip. Any other thoughts??

Opening or closing those contacts with a load on them will do this, the higher the load the more arcing. Closing them into a short circuit may result in even more serious damage.

 

[GoldDigger]

Opening or closing those contacts with a load on them will do this, the higher the load the more arcing. Closing them into a short circuit may result in even more serious damage.

So if you regularly test your GFCIs you probably should not do that with a heavy load turned on?

 

[kwired]

So if you regularly test your GFCIs you probably should not do that with a heavy load turned on?

I really don't know what kind of switch rating they typically have, but at same time the more load the more arcing there will be, and if there is motor load that can be a little harder on them as well.

 

[JFletcher]

I have not disassembled any of the many failed GFCI receptacles I've removed. I'm not sure that ones built 20+ years ago are even designed like ones made now (ofc now they self test too...). A good 80% of the ones Ive seen failed were outdoors... dunno if in-use covers will keep a new WR GFCI good 20+ years from now.

The older ones can fail in a lot of ways. I believe mbrooke posted a video not too long ago of one (ca. 2010) where the ungrounded side welded itself together and was still passing current even in a tripped state.

For whatever reason, GFCI receptacles of any age seem to have a high failure rate. Since they cant be rebuilt or field serviced, I concern myself with whether they work or not, not what causes them to fail.

 

[iwire]

So if you regularly test your GFCIs you probably should not do that with a heavy load turned on?

Per the UL white book unless the test buttons are also marked on and off they have no switch duty rating.

That aside we used one in our kitchen to control an under cabinet light for years.

 

[iwire]

Since they cant be rebuilt or field serviced, I concern myself with whether they work or not, not what causes them to fail.

:thumbsup:

 

[GoldDigger]

Per the UL white book unless the test buttons are also marked on and off they have no switch duty rating.

That aside we used one in our kitchen to control an under cabinet light for years.

And I must admit to once using an inside GFCI receptacle to control (on/off) an outside receptacle downstream on the circuit which we used for Christmas lights. Especially when it was raining.

I did not know that the inside GFCI was upstream of the outside receptacle until it tripped one day from an extension cord end lying in wet grass.

 

[kwired]

I have not disassembled any of the many failed GFCI receptacles I've removed. I'm not sure that ones built 20+ years ago are even designed like ones made now (ofc now they self test too...). A good 80% of the ones Ive seen failed were outdoors... dunno if in-use covers will keep a new WR GFCI good 20+ years from now.

The older ones can fail in a lot of ways. I believe mbrooke posted a video not too long ago of one (ca. 2010) where the ungrounded side welded itself together and was still passing current even in a tripped state.

For whatever reason, GFCI receptacles of any age seem to have a high failure rate. Since they cant be rebuilt or field serviced, I concern myself with whether they work or not, not what causes them to fail.

Shortly after they started requiring WR receptacles, I seemed to have a increase of failures of GFCI receptacles of WR types. I wasn't sure what the issue was, they just stopped working. I haven't had one for quite a while now. It was only maybe 6 devices that failed in about a years time, but that is a high number considering the failure rate I had within a couple years after initial install was pretty much zero for many years with P &S GFCI devices.

 

[Marty Lustig]

More on GFCI Failure Modes

More on GFCI Failure Modes

I'm new to the forum, so I may not have added this additional information correctly.

All of your replies are helpful.

JFletcher's reminded me I had left out some key info.

When I discovered the GFCIs were bad, prior to disassembly, one of them was still passing hot and neutral to the downstream receptacles. But when tested at the GFCI blades, it suggested an open neutral. Indeed it is the one where one set of "springy" contacts had welded closed.

 

[JFletcher]

I'm new to the forum, so I may not have added this additional information correctly.

All of your replies are helpful.

JFletcher's reminded me I had left out some key info.

When I discovered the GFCIs were bad, prior to disassembly, one of them was still passing hot and neutral to the downstream receptacles. But when tested at the GFCI blades, it suggested an open neutral. Indeed it is the one where one set of "springy" contacts had welded closed.

Welcome to the forum (didnt see your post count/join date).

Ive seen about every imaginable failure from older GFCIs, including powering downstream receptacles (both sides, a complete circuit) even when tripped. Some of these were line/load reverse wiring errors, most were failed receptacles. Most bad ones just wont reset for whatever reason. As you've noticed, there are a lot of parts in a GFCI, and moving parts. Electronics. Things just fail. While I enjoy failure analysis, unless the same receptacle was constantly blowing out, I wouldnt be too concerned with the specifics of the failure, just replacement. It's good to know that they can fail, and not in a failsafe manner.

The new ones self-test, and lock out on failure; much better than finding out the hard way the GFCI protection you think you have is compromised and non-existent.