What are the different classes and how to determine what class an appliance is?

Class I equipment is constructed such that protection against electric shock does not rely on basic insulation alone. In addition to basic insulation around live internal parts, exposed conductive parts are connected to the protective conductor in the fixed wiring of the electrical installation. Class I equipment relies upon a connection to the protective conductor to prevent exposed conductive parts becoming live in the event of a failure in the basic insulation.

Class II equipment is constructed such that protection against electric shock does not rely on basic insulation alone. In addition to basic insulation around live internal parts, supplementary insulation is provided, there being no provision for connection of exposed conductive parts to the protective conductor. Such equipment is often described as “double insulated” and should carry the symbol.

So essentially Class I equipment has an earth which will be visibly terminated in the plug top & has an earth incorporated in the supply cable. Class II equipment does not rely on an earth connection for safety therefor inside the plug you will only see 2 wires (L+N) & is supplied by a 2 core cable.