Ive just built a summerhouse at the bottom of the garden and am now running swa down the garden to power it. The maximum sized cable I can get hold of easily is 4.0mm. I need to up the load capacity as I will be running electric heaters, tv, pc, etc etc down there. Now, the question I have is whats the rule of thumb with running cable in parallel connected at either end? I assume that if I run 2 x 4.0mm cables in parallel that is equvalent to 1 x 8.0mm right?