Many of the Electricians i have worked for/with have made joints in the back of switches, but you must be careful what method of joint you use in order to comply, the NIC "snags and solutions" book mentions use of Connector strip but suggests that it has sufficient insulation on it and is fixed. There is a nice picture of some "choccie block" with an extra layer of insulation bolted to the back of the enclosure (box), i have never seen this done! i would imagine that it is too time consuming. I have heard that people have glued them in order to satisfy inspectors!! Other sparks use crimps, but others say that the through crimps leave an open end. There are some push fit connectors available where 2/4 or 6 cores can be inserted and they are closed and although i have never used them i know guys that have and tell me that the NIC like them, However i can't find any info on them right now!! so i'm not much help am i ?