Hi I have 20 spike spot lights that I want to install for garden borders. They will be fitted with GU10 led bulbs The run of the flex will be around 50m after the connection to the armoured cable which will be around 12m. What flexi cable should I be looking for? And do I use 1.5mm? I presume I need 3 core because the spots are stainless steel. The cable will be pinned to fences so no need for armoured.