How to Select a DC Combiner Box for Rooftop PV Strings

Rooftop photovoltaic arrays mix many DC strings into a single output before the inverter. The combiner box is where that work happens, and the wrong enclosure or fuse map shows up later as nuisance trips, water ingress, or an inspection delay.

Match string count to the enclosure, not the other way around

Start from the array layout. Count the strings that actually land in one box, then add spare glands for a future string rather than filling every pole on day one. Pronto KNX5PV-class enclosures are built for this: IP65 housings, bottom cable entry, and room for fuse holders plus a Type 1+2 SPD without crowding the DIN rail.

Fuse and voltage ratings have to follow the module string

A 1000 V DC string needs gPV fuse links and a holder rated for DC interruption, not an AC cartridge borrowed from a lighting board. Check Isc of the module, apply the local multiplier, and keep the holder lever visible so isolation is obvious during maintenance.

What to send with the enquiry

String count, Voc and Isc, target DC voltage, indoor or rooftop mounting, and whether SPD is required in the same box. With those five points an OEM or project pack can be quoted without a second round of drawings.