Can you safely connect the LED side of an optocoupler to AC Mains(120v)?
Though not ideal, each 100 kΩ resistor, by itself, would limit fault current to ~1.2 mA, generally considered safe on skin contact. Of course, a resistor failure could make the the circuit &quot;live&quot;... but if the optocouplers are in an effective enclosure, and the only wires or traces leaving enclosure are from the output side, the 5,000 V isolation specification should make this safe.
That said, typical on current for the LED is 10 mA to turn the output completely on. At 120 VAC, two 100 kΩ resistors would limit current to ~600 µA, which might not provide sufficient drive.