Hi, I have a first fix radial in 4mm t&e cable, in place ready for the sockets to be connected. One of the sockets has a spur of it, again in 4mm t&e. Therefore there are three 4mm cables coming out of the backbox. How on earth! do you connect three 4mm cables into the socket. I can only just get two 4mm cables in, then tighten the screw to hold them