GFCI breaker tripping at floor box

[Dennis Alwon]

It would be nice to know what the op found @Shujinko

 

[jmoschetti45]

It's the surge suppressor(s). We've talked about this here before, you can't use surge suppressors on a GFCI circuit or with a GFCI receptacle. It's going to cause random tripping. Nothing to do with cheap or failing surge suppressors either, except maybe the cheap ones that don't do much will work.

From a surge suppressor design point of view, I've ALWAYS thrown a gas discharge tube in series with any MOV tied line to ground, or neutral to ground. GDTs have "no" leakage current until they reach breakdown voltage, which then lets the MOV dump as much current as it can handle. MOV ages, gets damaged, etc, there isn't an issue with tripping. Also reduces the unfriendly tingle from aging equipment people have removed the ground prong from.

 

[hbiss]

From a surge suppressor design point of view, I've ALWAYS thrown a gas discharge tube in series with any MOV tied line to ground, or neutral to ground. GDTs have "no" leakage current until they reach breakdown voltage, which then lets the MOV dump as much current as it can handle. MOV ages, gets damaged, etc, there isn't an issue with tripping. Also reduces the unfriendly tingle from aging equipment people have removed the ground prong from.

Don't know that I would agree with what you say is going to help because we are not talking about leakage. Spikes and transients cause the normal operation of the device and it's the normal operation that trips the GFCI.

Also, we have nothing to do with the manufacture of surge suppressor devices so unfortunately your design advice is of little use here. Not that it isn't appreciated, of course.

-Hal

 

[kwired]

Shouldn't the MOV have no leakage until you reach a peak voltage above some threshold that should be above nominal operating volts?

If adding GDT you would still need one designed to conduct once you reach your design threshold.

Higher design threshold you are willing to allow the less either would result in GFCI trips, presuming the transient itself doesn't cause the GFCI to trip.

Still sold more on having surge protection at the main panel which may lessen other surge related issues at branch circuit level, but still suggest point of use protection at certain equipment.

 

[Russs57]

MOV's get damaged over time and leak more and more. They really should have a thermal switch in series along with a LED to let you know when thermal switch has made them inactive. GDT don't seem to get damaged as much by repeated hits. However they (typically) don't respond quite as fast.

 

[synchro]

From a surge suppressor design point of view, I've ALWAYS thrown a gas discharge tube in series with any MOV tied line to ground, or neutral to ground. GDTs have "no" leakage current until they reach breakdown voltage, which then lets the MOV dump as much current as it can handle. MOV ages, gets damaged, etc, there isn't an issue with tripping.

While GDTs will have lower leakage than MOVs, once you have a GDT I'm not sure what the advantage would be of putting an MOV in series with it. The resulting response time will be limited by the slower response of the GDT that Russs57 has mentioned. But the current handling and ability to dissipate the surge energy will be limited by the MOV because it will have a much larger share of the voltage drop once the GDT breaks over. So I don't see the advantage of the of the series combination over having the GDT alone.
Now having a shunt GDT, a series impedance such as an inductor, and then a shunt MOV to form a "pi" network can be very effective as described in the app note linked below. The MOV reacts quickly to clamp the beginning of the surge while the current is limited by the series impedance, and then the GDT breaks over and limits the pass thru voltage to low values in spite of very high current levels.

EC640.pdf

 

[jmoschetti45]

MOV's get damaged over time and leak more and more. They really should have a thermal switch in series along with a LED to let you know when thermal switch has made them inactive.

They do. At least 2 manufacturers have them in their lineup. I know Littelfuse is one (TMOV series...ones I always use. Built in thermal cutout and indication lead) and another I can't remember right now.

You need the MOV in series with the GDT...once a GDT strikes an arc, the voltage would have to drop to near 0 for the arc to extinguish. This *shouldn't* be an issue with an N-G connection, assuming correctly wired and polarized plug, but we know the odds of that. If you have a GDT between L and N and it arcs over at let's say 150V, once the voltage drops back to 120V it's going to continue to arc until it self destructs or OCPD kicks in.

 

[kwired]

While GDTs will have lower leakage than MOVs, once you have a GDT I'm not sure what the advantage would be of putting an MOV in series with it. The resulting response time will be limited by the slower response of the GDT that Russs57 has mentioned. But the current handling and ability to dissipate the surge energy will be limited by the MOV because it will have a much larger share of the voltage drop once the GDT breaks over. So I don't see the advantage of the of the series combination over having the GDT alone.
Now having a shunt GDT, a series impedance such as an inductor, and then a shunt MOV to form a "pi" network can be very effective as described in the app note linked below. The MOV reacts quickly to clamp the beginning of the surge while the current is limited by the series impedance, and then the GDT breaks over and limits the pass thru voltage to low values in spite of very high current levels.

EC640.pdf

Was somewhat what I was thinking, doesn't seem to be an advantage of putting those two items in series with one another. Your needs can be one or the other but can't really get best of both at the same time.