Trying to understand DC MCB Fault scenarios and handling

[LionKing]

Got this DC MCB rated for 1000v and 20a (datasheet attached). Under "Wiring method for ungrounded system", it shows Fault scenarios:



If I'm understanding this correctly, if the breaker will only trip if there is more than 20A between its positive and negative. If there is more than 20A between positive - PE OR negative - PE, then it won't trip. Is that right?

In my case, I have one series string (Voc: 580, Isc: 14.01) connected via this breaker to inverter. Should I add 20A fuses on positive and negative of string before the breaker as well, just for some extra protection?

 

[timselectric]

With only one string, no protection is required.
The solar panels are self limiting.
This breaker is just being used as a disconnect.
Fuses would also serve no purpose.