gertc

Thanks all
@Chris - it is only the one CB that trips

For now I am guessing that it is a faulty CB which I will get the installer to replace.  I will also check the combiner boxes with him.
Thanks again for the help and will post back once resolved.

Gertc a quick explanation for the combiner box
"In all but the smallest PV systems, modules are wired together in series strings, where the positive leads of one module are connected to the negative leads of the next module. This results in cumulative voltage output, with current (amps) staying the same. The box where the output wires from multiple series strings are joined is the combiner box. Rated for outdoor use, it contains overcurrent protection devices (OCPDs) and the necessary bus bars and terminals for combining the inputs."
What we add extra normally are fuses per string and some of us even have breakers/disconnects for each string.
The combiner box should be located before the DB with your 3 Noark 40A breakers. Most of the time closer to your panels to keep the wiring to a minimum.
For you I would expect 3 separate ones to keep it neat and tidy.
Your Noark breakers are DC breakers so all should be fine.
 
Edit: Might even have one faulty 40A breaker?

Hi Gertc
 
Please send model numbers of your breakers used on the strings.
If possible maybe even a picture of the inside of your combiner boxes.
12A per string also does not make sense to me, how are you measuring this?
The voltages lets me think you have 4 strings of 2 panels per string

This does not make sense at all. Does this happen on all 3 inverters or perhaps only on one of them?  The short circuit current per panel is only 9A, so for 3 parallel strings it will be 27A @ 1000w/m2. Say you have clouds and the cloud effect, you might get up to 25% more from the panels - then they would give you 11.25A per string, 33.75A per set and that is at short circuit, so the V would be 0.  You get 20V per panel when this happens, so you are running at less than short-circuit current. I cannot explain why you would measure 12A per string and how a 40A breaker will trip.
I'm going with Chris' comment, probably the breakers are not DC rated.

If you using the Axpert to report PV current then there is an anomaly within Axperts in that they report PV volts before the MPPT and PV Amps after the MPPT. So in my case it often reports 44A whereas if you do the calculation it is closer to the maximum of 32A for my PV array. I have 12x250W Yingli panels in 4 strings of 3 and never have any hassle with a 40A DC breaker. The voltages you are seeing seem a bit low. I would expect to see figures of 68 to about 75V at maximum power and your Isc is 9.09A so I would not expect anything over 28 -29 A. Are you sure your breakers are DC rated? (It is not DC rated unless it says so on the outside- don't let some wiseass electrical supplier tell you it is DC rated check for yourself). That is the only thing that I can think of. You low PV panel voltage troubles me but I cannot put my finger on it. There may be a wiring fault somewhere. Did you use a contractor to do your install or is it DIY? 

Thanks Gustavo
 
Appreciated the feedback - I will try the settings on 12 & 13.  On 26 & 27 - I have Sonic Gel batteries and if I look at their manual and it seems like these are the values for their cycle and and float values - any reason why you are suggesting different values here?