This model is rated at 7.4kW. I have run a new 6mm cable 15 metres long from a 40 amp mcb to a 45 amp DP cooker switch. My problem is that the flex that came fitted to the hob has four wires...y/g, brown, blue and black. It seems clear that y/g is earth, blue is neutral and brown live but what is the black for? I've tried AEG and Service Force and they are most unhelpful.Your help would be appreciated