I would like to get your opinion as to what could be the cause of the below cases happening in the same solar plant.
1.Case 1: burning of junction boxes of all PVmodules including its diode in a string of 21 PV mod.
2.Case 2: In some cases the burning of MC4 branch (Y)connector that joins two strings in parallel or some cases the MC4 connectorsat PV modules.
Initially it seems to be problems of improper terminations or crimping of MC4 but looking at how the strings are protected with fuse I beginning to see some other issues.
There are 21 strings in a combiner box (with 21 module perstings with an Isc rating of 9A per module or the string) .These 21 strings are then wired in pairs.A total of 10 pairs of string (tied togetherwith a MC4 branch connector at the field) and a 30A fuse protection per pair atthe combiner box. Then the remaining one (1) single string is protected with15A fuse (although the drawings says 30A) I have attached a single line diagram on how it was wired.
It seems that the 30A fuse will never protect a single string if a fault will occur in any of the string.