If you want a good idea where it's not, look here:
The large silver area is where a failure took off the solder mask. The failure was of a capacitor connected across the mains. That solder mask is connected to circuit (and mains) ground.
When the capacitor failed, it *may* (it did not, as it happened) have produced some connection between mains active and circuit ground. In this case that would have tripped an ELCB, but in other cases it might have had worse results.
It is important that you maintain adequate clearances, and that depends on the voltage. The ground plane may be fine around the relay coil contacts, but unless it is connected to protective ground, I would keep it well away from 230VAC. If it is absomutely required for shielding, then you MUST observe the requirements for
creepage and clearance.