Greetings, my wife would like a double gang socket in the potting shed for her heat mat for the plants and other very low voltage items with no lighting required - just a double gang socket. So my plan was to add a fused spur to a ring main, run some domestic 2.5mm T&E through an external wall straight into an IP rated junction box and make a connection to a 20 metre run of SWA cable. There are no other forms of power in the shed, and no metal pipes etc. What sort of size does the SWA need to be? I've read sizes of 6mm and 10mm for this kind of run but if it's only a double gang socket with low voltage items is that sort of size necessary or does the distance form part of the calculation? Should the fused spur have an RCD or is it better to have a RCD double gang socket at the shed? And in terms of earthing, the fused spur is in a dry lining plastic junction box on the ring main, the external IP rated junction box is plastic, and the cable will likely terminate at another plastic junction box or isolator switch in the shed and join to domestic T&E for ease of use so what is the best method of earthing either a dedicated earth wire or the armour? The cable will run alongside a wall and it will be tricky to bury so if it gets tacked to the wall does it have to be in trunking or conduit even though it seems safer in view rather than buried 240mm down? And in terms of the part P certification and the BC etc, is it true that it is only needed if a brand new circuit is attached to the CU, and not for a spur such as this? Sorry lots of questions but hopefully valid ones. Thank you in advance for your help.