I have created a home automation panel running several ESP32’s that is powered using a POE splitter. The entire setup is mounted in a PLC type cabinet with din rails. My question is should I ground the metal cabinet? I can easily connect the metal cabinet to my house ground, but is this recommended? Again, everything is powered via a POE splitter at 5VDC. There is no AC current in the panel.
Ask an electrician in your country.
Depending on the switch and splitter isolation it would be unlikely to be required under the Australian wiring rules.
However earthing it would not hurt and would protect people from the very unlikely event of a mains fault in the switch traversing the PoE splitter and then coming in contact with the cabinet.
Many regulators consider <50V as SELV and if conditions are met, equipotential bonding is not required for safety:
Personally, I’d ground the cabinet as faults happen (as long as you have ELCB / GFCI upstream), and grounding can help with RF interference and even external events like static / lightning.
Just be careful insulating connections inside the box (wooden back plates are useful, less relevant for DIN rail), and consider different ground references.
If you have several PoE or LV power supplies, not all may be referenced to the same ground point, leading to surprising differences between 0V / GND / Vdd (a big issue with multi-phase and different buildings - fibre Ethernet helped a lot).
I’m curious as to why you added the importance of upstream GFCI.
Basically, grounding works best when a fault condition is detected quickly by a ELCB / GFCI spotting current flowing via ground before someone gets hurt.
If there’s no ground leakage detection (such as a LV PSU going bad), it can be better to NOT ground - that way, touching a case won’t complete a circuit. In the UK, the case could be classed as an “extraneous conductive part”
To complicate matters, telecoms kit often has a “Functional Earth” separated from mains earth to dissipate induced voltages over long wires rather than prevent electric shocks. The cream functional earth is not connected to yellpw mains earth as that can induce AC mains hum.
If this helps, 
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