The main switching cabinet has protection class IP66 (Dust tight, no harm from powerful water jets), assuming you install the cable inlets correctly.
However especially in humid or salty environments (e.g. near the sea), or where insects are a problem, it is recommenced to protect the PCB additionally.
This Aluminum casing has protection class IP67 (Dust tight, water tight up to 1m immersion equivalent)
Also since this casing is made of metal, it also protects against EMC and EMI disturbances.