Design
A BS 1363 plug has two horizontal, rectangular pins for line (commonly termed "live" or "hot" in the United States, but "line" is the term used in BS 1363, per British practice) and neutral, and above these pins, a larger, vertical pin for an earth connection. Unlike most other types of sockets, the earth pin is necessary for use of the BS 1363 plug, as it is needed to push open a shutter in the socket to allow the line and neutral pins to be inserted. It also polarises the plug, ensuring that the line pin is connected to the correct terminal in the socket. Moulded plugs for unearthed, double-insulated appliances may instead have a non-conductive plastic pin (an Insulated Shutter Opening Device or ISOD), to open the shutters.
BS 1363 specifies the dimensions of plug pins and their disposition with respect to each other in precise, absolute terms. BS 1363 sockets are required to mate correctly with BS 1363 plugs (as opposed to the dimensions of the socket contacts being specified). This is checked by means of the use of various gauges which are specified in the standard; these gauges ensure that the socket contacts are correctly positioned and make effective and secure contact with the plug pins. There is no provision for establishing the interchangeability with any other device having plug pins incorporated, but which is not covered by BS 1363 (for example a charger or socket cover) unless that device conforms precisely to the plug pin dimensions specified.
Read more about this topic: BS 1363
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