A Combiner Box is an electrical distribution box where multiple series of solar PV modules are connected and combined in parallel into one DC output. Combiner boxes used in off-grid systems generally use DC rated breakers. Combiner boxes used in Grid-tie solar applications use 600VDC rated fuses. Please note that fuses, breakers and in some cases fuse holders need to be purchased separately. In order to choose the correct combiner box, it is necessary to determine the number of strings of solar panels, as well as the breaker or fuse size. A typical fuse or breaker size is 15 – 20 Amps.