South African Derivatives
The South African SANS 164 standard defines a number of derivatives of this plug. The main household plug is defined in SANS 164-1, and is essentially a modernised version of BS 546 (the essential differences are that pins can be hollowed to reduce the amount of metal used, the dimensions are metricated, and it is rated 16A).
SANS 164-4 further defines three variants of this plug intended for specialist (known as "dedicated") applications. The variants use a flattened earth pin, each at a different specified rotational position. This arrangement ensures that the dedicated plugs can all plug into an ordinary ("non-dedicated") socket, but that the various dedicated plug and socket combinations are not interchangeable (nor can a non-dedicated plug be inserted into a dedicated socket).
The dedicated versions have specific colours assigned to them, depending on the rotational position of the flattened portion. These are black (-53°), red (0°), and blue (+53°). The red (0°) version is by far the most common, and is widely used on computer and telecommunication equipment (although this is not required in the standard). In this application the "dedicated" socket refers to one that is not connected to a residual current circuit breaker, which is otherwise mandated for all normal power sockets.
Read more about this topic: BS 546
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