Using a relay to switch between 230VAC inputs
The relay coil must be for 230 V AC. Most relays are for voltages less than 24 V, and also DC. An AC relay will consume less power.

The contacts must be for 250 V AC minimum. But your demands are different than for a common 250 V contact. If there's a spark over an open contact in a normal serial switch application then no harm is done, because the circuit is designed to allow current through the contacts anyway. But that's not the case here: a spark between two contacts may cause a short circuit.

Also if the second power source is a different phase of the 230 V then you can have 400 V between the two contacts. It would be better then to have the neutral and the phase of V1 on one contact and the phase of V2 and the neutral to the other contact. So not the two "-" together, but the "-" of one to the "+" of the other one.

In any case I would recommend using a 500 V relay.