Hi. I bought a proline ceramic hob for a building we're completely renovating. Man doing my electrics (not specialist electrician) installed 6mm cable because 6Kw rated hob. Hob installation instructions say 2.5mm cable is needed and in fact the 6mm cable doesn't fit to the connectors on the hob. Man doing my electrics spoke to proper electrician who said can only have one ring on at a time if 2.5mm cable. Comet (where I bought it) says follow instructions. No-one else has complained. Can anyone tell me who is right?