GFCI/AFCI breakers fail self-test when running from inverter only

[joe_s]

Hi All - bit of a unique situation here. I am building a tiny house at a "construction site" (warehouse) and I have the 18kPV installed and all the wiring before and after my panel is complete. I do not have solar or batteries installed, yet. This warehouse only has single phase 120 readily available, so to test my electronics I have been paralleling the two legs of the panel and running my 120 circuits with no issue. This is shown in the diagram as "Run from extension cord (grid)". I really wanted to test the inverter and run my hot water heater heat pump so I bought a 52V AC-DC power supply to act as a "battery" and run the inverter from. This is shown in the diagram as "Run from inverter" and all worked great! I was able to commission the inverter and my leg voltages look good, and ran ~1kW through it for the hot water heater. However, my 120 breakers are all combo GFCI/AFCI (Eaton CUTCHFP120DF) and after I start running the panel through the inverter, they all click off after 3-5 minutes (not all at once) and give me a 6-light error code which means the breaker failed an "internal self test". When I revert to extension cord power, the breakers are fine, indicating to me they are not permanently damaged. The fact that the breakers are ok in extension cord mode also leads me to believe that all the branch circuit wiring is fine and there are no actual faults within it.

To note:

• I previously received a VBUS over range error once but I am not sure under what circumstances and I cannot find any link between that and the occurrence of the breaker issue
• My 240 GFCI only breakers (ex: to run the hot water heat pump) do not trip and do not have the self test issue, leading me to believe it is an issue with the AFCI self test feature

My leading hypotheses:

• Ground-neutral bonding issue (though I did try different bonding conditions)
• The inverter AC waveform has some harmonics in it or is distorted just enough that the electronics in the breakers can't operate on it

Next tests to try:

• Run from 48V battery instead of power supply (to rule out ground-neutral issues)
• Bus capacitance added to the output? Investigate AC waveform cleanliness
• Firmware update (I have not updated after unboxing in November 2024)

Can anyone speak to this issue or offer some hypotheses and/or solutions?

Cross posted on EG4 forum: https://forum.eg4electronics.com/co...il-self-test-when-running-from-inverter-only/

 

[wheelman55]

Try using some GFCI breakers.

The combi breakers trip too easily.

 

[joe_s]

The question was aimed at trying to use the combo breakers. I have about 13 of them installed at $75 each so I don't want to give up on close to $1k of hardware, and also lose out on the AFCI protection on outlet/lighting circuits where they add safety

 

[wheelman55]

Joe. We’ve got more than 20 of the combination breakers, SquareD QO in our case. I replaced the problem breakers with GFCI.

We are 100% off grid.

I suggest that you replace one as an experiment. The breaker running your refrigerator would be a good choice

I’m not an expert. It reads from your description that the breakers trip when running through the inverter. Is this correct?

If this is the case, something within the inverter is likely causing the combo breakers to trip.

Certain power tools were tripping my breakers. Larger drills for example. Also had a strange tripping breaker from a Dewalt chop saw that I had been using trip free, from the same outlet, for over 1,000 board feet of lumber.

It turned out that I had a charger for my e-mtb plugged into the circuit. The bike wasn’t attached. Somehow the combo of the saw with the charger caused the tripping. I unplugged the charger and the saw works as it should.

I replaced something like 4-6 of the combo breakers. We do still use 20+ of the combo breakers.

We have Schneider gear. XW+ inverter, 80-600 MPPT and mini pdp. No issues once the problem breakers were replaced.

Good luck…these are head scratchers for sure.

 

[joe_s]

I did some troubleshooting with an oscilloscope and have some interesting results.


Here is a summarized test matrix and results:

• Run from wall (extension cord) --> waveform looks ok, breakers won't trip no matter what combination of loads is on
  
• Run from inverter, low load (150W) --> waveform looks AWFUL, a bunch of high frequency harmonics near the peaks. The breakers will eventually all trip off with the same "self-test" error code. Turning on LED lights seems to push them over the edge but they will trip lights or no lights eventually. During this portion I also received a VBUS OverRange Error. My hunch is that those harmonics are exceeding the internal VBUS limits, but I'm not sure. I was running an FFT on the scope and there is the peak at 60Hz but also smaller peaks at ~2kHz and likely the first harmonic of that at ~4kHz
  
  
• Run from inverter, more load (~1000W) --> I loaded up the inverter using the heat pump and those harmonics went away, the waveform clears up, and the breakers were happy and didn't click off (across the 20 minute test or so). No VBUS OverRange error either
  

I received some motor-run capacitors I am going to try and parallel into the output to see if that helps. My hypothesis is that this could just be "loading up" the inverter in the low load cases with reactive current which could help.



My batteries are coming next week but have a few more weeks of commissioning before I can get them working, at which point I'll run another test and see what happens.