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That's interesting...I did not know that. How does that affect the functionality of the circuit?
As it is now you're good for star shaped nets as reverse voltage would stay across the 1N4004 diode, but for a delta shaped net you will develop reverse voltage across the led when the two phases reverse polarity. Typical reverse breakdown voltage for a led is around 50V and I see nothing in the YTLP781 datasheet to suggest it is different.
So you would need to protect the TLP781 led from reverse breakdown. This could be a reverse diode in parallel with the led or you could choose an AC photo coupler with dual opposite led's.