ditto, I use similar methods for all cable splicing (ELV, LV) but once over 4mm2 I use crimped butt splices instead of soldered joints. I picked up a hydraulic crimper off ebay for a decent sum, and it's good from 10mm2 up to 135mm2. 4 and 6mm2 crimps are done with standard electrical pliers (mine have a notch designed in for that purpose.