I'm by no means an Electrical Engineer but from time to time I have to do your typical DC wiring and soldering. But AC is a completly different beast to me, since I rarely have to interact with it.
That's why this was done: so I can get this information quicker instead of burning stuff down and / or having 230V - or read that as 120V if you leave in 'Murica - rushing though my heart.
With the Power Supply / Lamp / LIVE (BE EXTRA CAREFUL)
Set the Multimeter to AC Volts
Connect to 2 terminals
If you connected Phase and Neutral = 230 Volts
If you connected Phase and Earth = 230 Volts
If you connected Neutral and Earth = 0 Volts
So the same wire giving the 230 Volts reading will be the Phase (Live Wire)
Now you should know which one is the Phase so
Shut of Power Supply (SHUT IT OFF)
Set meter to Ohms
Connect between Earth and and another wire. If It reads 0 - or near - Ohms, that is Wire.