boora:
Please placeyour posts in the 'Non-US Electrical Systems Area".
Practice here in US is that any metal box, as well as the device be bonded to an equipment bonding conductor. That is either a bare, or green insulated conductor.
12/2 NMC(Romex) is 1-black insulated (hot); 1-white insulated (neutral); and 1-bare conductor. All are 12AWG.
