AFCI breaker issue on one leg of stacked SW5548s

Coyote0

Greetings,
I have parallel stacked SW5548s rev 4.30 firmware, which otherwise work well, but on one leg only Eaton BRP120AF breakers won't test trip, and upon manual reset blink self test failure.  The other leg has no problem.   On genset passthru power, both legs function with AFCI breakers.

Voltage, frequency, and waveform via small oscilloscope look identical on both legs. 
There are lots of parameters visible on the advanced tech menu output, and the values differ between the two inverters but I can't find any documentation on what they mean.

Is there a test and repair manual available for this model inverter?

Any ideas on why the malfunctioning breakers?

BB.

It sounds like it could be a "wiring" issue with the circuit breakers...

Combination Breakers (arc and and ground fault types) need both the Hot connections and the neutral to "pass through" the breaker.

A 120 VAC breaker:

L1 In------Circuit---- L1 Out
Neutral---Breaker---Neutral Out

A two pole breaker (120/240 VAC split phase):

L1 In------Circuit---- L1 Out
L2 In------ 2 pole----L2 Out
Neutral---Breaker---Neutral Out

If you do not have the Neutral In connection to the bus bar--You can fail self test. If you do not have the Neutral Out to L1 or L1+L2 branch circuits, then you should have false trips (any loads applied to branch circuit trip the ground fault interrupt function.

Tradition circuit breakers do not use a Neutral connection... So for GFCI and combo AFCI breakers have either a pigtail attached, or plug into the neutral bus bar (looks like the breaker+panel you have?). 

You have stacked inverters--So, just to confirm, you have a common Neutral to both inverters' neutral connections...

Anyway--My first guesses.

-Bill

Coyote0

Yes, I have a common neutral, and also neutral and ground are bonded at the load center.  The battery bank negative is also tied to ground, but at the inverter power panel.  This was the recommended installation procedure years ago.  I can't see how it would make a difference since presumably the battery negative and neutral are isolated from each other in the inverters.

This is a combination breaker. I wonder if it would make sense to try an AFCI only breaker. The newer Eaton BRs are AFCI only I believe.

RCinFLA

AFCI's probably will not like the stepped sinewave of SW5548's.  AFCI's work by high frequency noise created by things like frayed extension cords arcing.  It might just be one AFCI is more sensitive or one SW5548 is more noisey in high freq noise than other.  

There are a maximum of 27 steps to the SW5548 sinewave but it is usually less based on ratio of battery voltage to grid voltage.  The coarser the steps the more high frequency noise in its AC output.  It is highly likely that as that ratio of battery voltage to grid voltage changes the amount of high frequency noise will change over time and how AFCI will react.  The results will likely be sometimes AFCI holds, sometimes it pops.

Not many options other than getting rid of AFCI's, at least on branches fed by SW5548's.  You might try different AFCI's to find one less sensitive.  Perhaps some AC line filtering on SW5548's output will clean it up enough to prevent AFCI's from tripping.  Any filtering has to be an actual filter of AC freq, not just a common mode line filter.  The EMI filter chokes in the SW power board is common mode filter.  There are two parallel 47 ohm resistors in series with a 1.5 uF cap on this board where AC wiring connects.  Make sure the 47 ohm resistors are not burnt out which would eliminate the filtering contribution by the 1.5 uF cap.  The small AC power board is fairly easy to access and work on.

Coyote0

A GE AFCI breaker test trips OK on the "bad" leg, however its not legal to use in an Eatonpanel apparently.  So I have a solution, just not an easy one.