What is the difference between AC-7a and AC-7b when choosing a iCT contactor?

These utilization catagories determine what load the contactors are switching:
AC-7a are for slightly inductive loads for household appliances for example mixers and blenders
AC-7b are for motor-loads for house hold appliances such as fans and central vacuums

The following is an extract from the IEC EN 61095 detailing the Utilization catogories for Electromechanical contactors for household and similar purposes

Released for:Schneider Electric UK