Class 0 Plug and Socket
In addition to the hexagonal Class I and Class II plugs and sockets, Appendix A of the standard also defines a 2-pin plug and socket with oval profile, for countries that still permit the use of Class 0 appliances, which are considered unsafe in most industrialized countries today. The Class II plug fits also into Class 0 sockets; it is up to national regulations of countries using the Class 0 socket, whether they permit an additional dummy hole in it, such that even Class I plugs will fit. However, none of the Class 0 plugs fit into a Class I or Class II socket. This way, the system prevents that Class 0 equipment can be operated easily in regions that do not permit such devices. The full mateability matrix of all plugs and sockets defined in IEC 60906-1 looks like this:
| fits into | Plug | ||||
|---|---|---|---|---|---|
| Class 0 (2 pin) |
Class I (3 pin) |
Class II (2 pin) |
|||
| Socket | Class 0 (3 hole) | Yes | Yes | Yes | |
| Class 0 (2 hole) | Yes | No | Yes | ||
| Class I (3 hole) | No | Yes | Yes | ||
| Class II (2 hole) | No | No | Yes | ||
As a result of the increasing global harmonization of electrical safety standards, IEC is phasing out the entire concept of Class 0 appliances from its standards. It is therefore unlikely that the oval Class 0 plug and socket variant will ever be introduced anywhere. The appendix that introduces it was probably merely added to address the concern that a system of country-independent plugs and sockets could permit the easy use of imported Class 0 equipment that does not meet national safety standards.
Read more about this topic: IEC 60906-1
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