Plugs and socket-outlets for household and similar purposes – A1: Multiway and intermediate adaptors, cord sets, cord extension sets, travel adaptors and fixed adaptors defines the requirements applicable to multiway and intermediate adaptors, cord sets, cord extension sets, and travel and fixed adaptors, it covers the electrical safety and user requirements, including the prohibition of stacking (the connection of one adaptor to another). Non-conforming products must be withdrawn from the Swiss market before the end of 2018. Pictures Thai three-pin plug TIS 166-2549 (Type O) Thai Industrial Standard (TIS) 166-2547 and its subsequent update TIS 166-2549 replaced prior standards which were based on NEMA 1-15 and 5-15, as Thailand uses 220 V electricity. The plug has two round power pins 4.8 mm in diameter and 19 mm in length, insulated for 10 mm and spaced 19 mm apart, with an earthing pin of the same diameter and 21.4 mm in length, located 11.89 mm from the line connecting the two power pins. The earth pin spacing corresponds to that of NEMA 5 and provides compatibility with prior hybrid three-pin sockets, which accept NEMA 1-15, NEMA 5-15 and Europlugs, all of which have been variably used in Thailand. The hybrid socket is also defined in TIS 166-2547, in addition to a plain three-round-pin socket, with plans to replace the former and phase out support for NEMA-compatible plugs. Sockets are polarised (as in NEMA 5-15). The plug is similar to, but not interchangeable with, the Israeli SI32 plug. The Thai plug is designated as "Type O" at IEC World Plugs. Comparison of standard types Adaptors Travel adapters Adapters between standards are not included in the standards, and as a result they have no formal quality criteria defined. Physical compatibility does not ensure that the appliance and socket match in frequency or voltage. Adaptors allow travellers to connect devices to foreign sockets, but do not change voltage or frequency. A voltage converter is required for electrical compatibility in places with a different voltage than the device is designed for. Mismatch in frequency between supply and appliances may still cause problems even at the correct voltage. Multisocket adaptors Multisocket adaptors allow the connection of two or more plugs to a single socket. They are manufactured in various configurations, depending on the country and the region in which they are used, with various ratings. In Europe for example, they are called double or triple adaptors,