The dead front on this MidNite combiner protects handlers from live wire terminals.
In the past, most PV combiner boxes simply had removable lids that covered the OCPDs and wiring inside. Although this configuration worked, with the box opened it didn’t protect users troubleshooting a blown fuse or tripped breaker. A misplaced screwdriver or finger could suddenly become an unwelcome conductor for 500 volts!
A “dead front” is a cover that allows access to the fuses and breakers, while shielding the operator from live wires and terminals. This cover may be a tinted or opaque polycarbonate plate (sometimes treated with flame retardant), which covers the entire opening except for the OCPDs (on OutBack and MidNite models), or simply small, clear plastic sheets that keep fingers and tools from accidentally touching live components (on AMtec models). Dead fronts are required on AC breaker panels, and we may soon see the requirement extended to DC combiners as well.
Many homeowners (and inspectors) require that all disconnects be lockable to keep out unwanted guests like vandals or curious children. It’s a good idea to be able to use a small padlock or something similar on the combiner box cover to restrict access.