SMPS floating ground safety

Question

I have a Mean Well SMPS (RS-15-12) with an isolated DC output. From my understanding, a floating ground is basically a 0V reference without any connection to mains earth (hence floating).

However, what if I have a protection diode that shorts the output to ground in case of polarity reversal (see attachment)? Would this still be safe, or should I connect the V- terminal on the SMPS to mains earth? (Note: V- on the schematic refers to a negative voltage, NOT the V- terminal of the SMPS).

These diodes are placed on the end (output) of a split supply, and are intended to redirect current to circuit ground (SMPS V- terminal) in case of polarity reversal during shutoff or component failure.

Help would be appreciated.

Answer 1

I have drawn this simplified model of an average smps ac/dc converter.
A transformer offers galvanic isolation, however an smps uses high frequency transformers for better efficiency, thus there will be switching noise. A capacitor is added across this transformer as path for this noise to go. The transformer itself may also have parasitic capacitance.

This capacitance generates some leakage current you will have present on the output referenced to the input and often Earth. In most cases this will present itself as a few µA of current, or without path around half mains voltage.

A diode between V- and PE will short this leakage current, if it's ratings allows.
I think this is not what you intend to do.

^{simulate this circuit – Schematic created using CircuitLab}

You can safely short V- to PE if your application allows it to be ground referenced.
Or replace it for a capacitor to remain floating but reduce V-/PE ac voltage.