Mains on a single core wire?
If you look around your house (in the walls, in fact), you will probably find many single core mains wires. They are reliable when they are fixed in their place, unlike cables.

If the wires can handle the current (what diameter are they?) and have proper insulation (thick enough for mains voltage), you can use them. The fact that they are single core helps prevent shortcuts due do small "stray wires". Make sure that you keep them at a minimum distance of about 2 mm. Use different colors for different lines. Keep them seperate from low-voltage/data wires.