How do you know if a combiner box requires a fuse or not?

Given an array with four inverters in parallel and 8 strings of modules (4 combiner boxes, 2 strings for each combiner box), do the combiner boxes need to be fused? Or can they just be pass through boxes to put wire into conduit?


The quick answer is no, as long as both strings have the same current output and there is no backfeed current available from the inverter side.

You have to provide overcurrent protection if the current available to a fault in a module is greater than the maximum series overcurrent protection specified by the module manufacturer. The source circuit and output circuit conductors have to be rated for any fault current they might be exposed to.