It is important to choose the correct size cable when connecting to the mains. The wire has to be the correct size so that it can cope with the power demands of the device. The size stated for cables is given in mm2 and this measurement is actually the cross sectional area of the wire inside. The larger that area the higher the current it can carry. 

If a cable is used which is too small for the amount of current passing through, it becomes dangerous. This results in the wire overheating and causing a serious safety risk. The table below gives typical values of cable size available plus corresponding current rating and maximum power ratings.