Potential danger using polarize DC breakers in combiner boxes

[BradCagle]

Anyone else realize this potential problem?

Polarized DC breakers such as the ones used in Midnight Solar MNPV combiner box have polarity. The + side must be connected to the highest potential, which would be the PV string. This is required for the arc suppression to function.








However if one of the PV strings becomes shorted, the other PV strings will feed into it, and the high potential for the shorted PV string may reverse. The shorted string breaker trips, the arc protection is defeated, and the breaker may burst into flame with an arc raging on.






Thoughts?

Anyone from Midnight Solar around to chime in?

 

[curiouscarbon]

good point

after learning about this failure mode, i decided that polarized breakers are unacceptable in any of my projects due to lack of robust arc quenching feature

eg

thanks

 

[realpinochet]

I just read about this also regarding double pole breakers with a polarity like the one he's holding Probably doesn't matter single or double pole. If you use them in between the battery and inverter and the inverter is a charger and is in the process of charging and the breaker pops it does something and potentially causes the breaker to short out and maybe catch fire.