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I assume the 230V circuit is a single phase and AC, is that correct?
If so, a few things would be needed:
- A full-wave (bridge) rectifier to convert the voltage to DC;
- A way to step down the voltage;
Then you could use either the digital I/O or analog I/O to determine whether the circuit is energized.
Some more information about the I/O capabilities can be found here (please note the voltage limits!).
After everything is connected physically, I/O Juggler (Services → Input / Output → I/O Juggler) can be used to set up a rule, that will send a message / send an email / trigger the digital output, etc.
Let me know if you need some more details on any part!